Database | Amazon ElastiCache for Redis Flashcards

Question 1

Q

What is Amazon ElastiCache for Redis?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Amazon ElastiCache for Redis is a web service that makes it easy to deploy and run Redis protocol-compliant server nodes in the cloud. The service enables the management, monitoring and operation of a Redis node; creation, deletion and modification of the node can be carried out through the ElastiCache console, the command line interface or the web service APIs. Amazon ElastiCache for Redis supports Redis Master / Slave replication.

Question 2

Q

Is Amazon ElastiCache for Redis protocol-compliant with open source Redis?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, Amazon ElastiCache for Redis is protocol-compliant with open source Redis. Code, applications, drivers and tools a customer uses today with their existing standalone Redis data store will continue to work with ElastiCache for Redis and no code changes will be required for existing Redis deployments migrating to ElastiCache for Redis unless noted. We currently support Redis 2.8.21, 2.8.22, 2.8.23, 2.8.24 and 3.2.4.

Question 3

Q

What are Amazon ElastiCache for Redis nodes and shards?

Features

Amazon ElastiCache for Redis | Database

Answer

A

An Amazon ElastiCache node is the smallest building block of an ElastiCache for Redis Cluster deployment. Each node supports the Redis protocol with Amazon’s enhancements and has its own endpoint and port. Multiple types of nodes are supported, each with varying amount of CPU capability, and memory capacity.

A shard is a collection of one or more nodes that is responsible for a partition of the logical key space. Within a shard, a node may exist in isolation or in a primary/replica relationship with other nodes. If there are multiple nodes within a shard, one of the nodes will take on the read/write primary role and all other nodes will take on a read-only replica role.

Question 4

Q

Does Amazon ElastiCache for Redis support Redis persistence?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, you can achieve persistence by snapshotting your Redis data using the Backup and Restore feature. Please see here for details.

Question 5

Q

How can I migrate from Amazon ElastiCache for Memcached to Amazon ElastiCache for Redis and vice versa?

Features

Amazon ElastiCache for Redis | Database

Answer

A

We currently do not support automatically migrating from Memcached to Redis or vice versa. You may, however, use a Memcached client to read from a Memcached cluster and use a Redis client to write to a Redis cluster. Similarly, you may read from a Redis cluster using a Redis client and use a Memcached client to write to a Memcached cluster. Make sure to consider the differences in data format, and cluster configuration between the two engines.

Question 6

Q

Does Amazon ElastiCache for Redis support Multi-AZ operation?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, with Amazon ElastiCache for Redis you can create a read replica in another AWS Availability Zone. Upon a failure of the primary node, we will provision a new primary node. In scenarios where the primary node cannot be provisioned, you can decide which read replica to promote to be the new primary. For more details on how to handle node failures see here.

Question 7

Q

What options does Amazon ElastiCache for Redis provide for node failures?

Features

Amazon ElastiCache for Redis | Database

Question 8

Q

Amazon ElastiCache for Redis will repair the node by acquiring new service resources, and will then redirect the node’s existing DNS name to point to the new service resources. Thus, the DNS name for a Redis node remains constant, but the IP address of a Redis node can change over time. If you have a replication group with one or more read replicas and Multi-AZ is enabled, then in case of primary node failure ElastiCache will automatically detect the failure, select a replica and promote it to become the new primary. It will also propagate the DNS so that you can continue to use the primary endpoint and after the promotion it will point to the newly promoted primary. For more details see the Multi-AZ section of this FAWhen Redis replication option is selected with Multi-AZ disabled, in case of primary node failure you will be given the option to initiate a failover to a read replica node. The failover target can be in the same zone or another zone. To failback to the original zone, promote the read replica in the original zone to be the primary. You may choose to architect your application to force the Redis client library to reconnect to the repaired Redis server node. This can help as some Redis libraries will stop using a server indefinitely when they encounter communication errors or timeouts.

Features

Amazon ElastiCache for Redis | Database

Question 9

Q

How does failover work?

Features

Amazon ElastiCache for Redis | Database

Answer

A

For Multi-AZ enabled replication groups, the failover behavior is described at the Multi-AZ section of this FAQ.

If you choose not to enable Multi-AZ, then if Amazon ElastiCache monitors the primary node, and in case the node becomes unavailable or unresponsive, Amazon ElastiCache for Redis will repair the node by acquiring new service resources, and will then redirect the node’s existing DNS name to point to the new service resources. Thus, the DNS name for a Redis node remains constant, but the IP address of a Redis node can change over time. However, if the primary node cannot be healed (and your Multi-AZ is disabled) you will have the choice to promote one of the read replicas to be the new primary. See here for how to select a new primary. The DNS record of the primary’s endpoint will be updated to point to the promoted read replica node. A read replica node in the original primary’s AZ will then be created to be a read replica in the shard and will follow the new primary.

Question 10

Q

Are my read replicas available during a primary node failure?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, during a primary node failure, the read replicas continue to service requests. After the primary node is restored, either as a healed node or as a promoted read replica, there is a brief period during which the read replicas will not serve any requests as they sync the cache information from the primary.

Question 11

Q

How do I configure parameters of my Amazon ElastiCache for Redis nodes?

Features

Amazon ElastiCache for Redis | Database

Answer

A

You can configure your Redis installation using a parameter group, which must be specified for a Redis cluster. All read replica clusters use the parameter group of their primary cluster. A Redis parameter group acts as a “container” for Redis configuration values that can be applied to one or more Redis primary clusters. If you create a Redis primary cluster without specifying a parameter group, a default parameter group is used. This default group contains defaults for the node type you plan to run. However, if you want your Redis primary cluster to run with specified configuration values, you can simply create a new cache parameter group, modify the desired parameters, and modify the primary Redis cluster to use the new parameter group.

Question 12

Q

Can I access Redis through the Amazon ElastiCache console?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, Redis appears as an Engine option in the ElastiCache console. You can create a new Redis cache cluster with the Launch Wizard by choosing the Redis engine. You can also modify or delete an existing Redis cluster using the ElastiCache console.

Question 13

Q

Can Amazon ElastiCache for Redis clusters be created in an Amazon VPC?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, just as you can create Memcached clusters within a VPC, you can create Redis clusters within a VPC as well. If your account is a VPC by default account, your Redis clusters will be created within the default VPC associated with your account. Using the ElastiCache console, you can specify a different VPC when you create your cluster.

Question 14

Q

Is Redis AUTH functionality supported in Amazon ElastiCache for Redis?

Features

Amazon ElastiCache for Redis | Database

Answer

A

Yes, Redis AUTH functionality is available on Amazon ElastiCache for Redis. At the time of Redis cluster creation via the console or command line interface, once you enable encryption in-transit, you can use the Redis AUTH command to provide an authentication token for communication with the Redis cluster.

Question 15

Q

How do I upgrade to a newer engine version?

Features

Amazon ElastiCache for Redis | Database

Answer

A

You can easily upgrade to a newer engine version by using the ModifyCacheCluster or ModifyReplicationGroup APIs and specifying your preferred engine version for the EngineVersion parameter. On the ElastiCache console, you can select a cluster and click “Modify”. In the “Modify” window select your preferred engine version from the available options. The engine upgrade process is designed to make a best effort to retain your existing data and requires Redis replication to succeed. For more details on that see here.

Question 16

Q

Can I downgrade to an earlier engine version?

Features

Amazon ElastiCache for Redis | Database

Answer

A

No. Downgrading to an earlier engine version is not supported.

Question 17

Q

How do I scale up to a larger node type?

Features

Amazon ElastiCache for Redis | Database

Answer

A

You can easily scale up to a larger node type by using the ModifyCacheCluster or ModifyReplicationGroup APIs and specifying your preferred node type for the CacheNodeType parameter. On the ElastiCache console, you can select a cache cluster or replication group and click “Modify”. In the “Modify” window select your preferred node type from the available options. The scale up process is designed to make a best effort to retain your existing data and requires Redis replication to succeed. For more details on that see here.

Question 18

Q

Can I scale down to a smaller node type?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Moving to a smaller node type is currently not supported.

Question 19

Q

What does it mean to run a Redis node as a Read Replica?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Read Replicas serve two purposes in Redis:

Failure Handing

Read Scaling

When you run a node with a Read Replica, the “primary” serves both writes and reads. The Read Replica acts as a “standby” which is “promoted” in failover scenarios. After failover, the standby becomes the primary and accepts your cache operations. Read Replicas also make it easy to elastically scale out beyond the capacity constraints of a single node for read-heavy cache workloads.

Question 20

Q

When would I want to consider using a Redis read replica?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

There are a variety of scenarios where deploying one or more read replicas for a given primary node may make sense. Common reasons for deploying a read replica include:

Scaling beyond the compute or I/O capacity of a single primary node for read-heavy workloads. This excess read traffic can be directed to one or more read replicas.

Serving read traffic while the primary is unavailable. If your primary node cannot take I/O requests (e.g. due to I/O suspension for backups or scheduled maintenance), you can direct read traffic to your read replicas. For this use case, keep in mind that the data on the read replica may be “stale” since the primary Instance is unavailable. The read replica can also be used to restart a failed primary warmed up.

Data protection scenarios; in the unlikely event or primary node failure or that the Availability Zone in which your primary node resides becomes unavailable, you can promote a read replica in a different Availability Zone to become the new primary.

Question 21

Q

How do I deploy a read replica node for a given primary node?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

You can create a read replica in minutes using a CreateReplicationGroup API or a few clicks of the Amazon ElastiCache Management Console. When creating a cluster, you specify the MasterCacheClusterIdentifier. The MasterCacheClusterIdentifier is the cache cluster Identifier of the “primary” node from which you wish to replicate. You then create the read replica cluster within the shard by calling the CreateCacheCluster API specifying the ReplicationGroupIdentifier and the CacheClusterIdentifier of the master node. As with a standard cluster, you can also specify the Availability Zone. When you initiate the creation of a read replica, Amazon ElastiCache takes a snapshot of your primary node in a shard and begins replication. As a result, you will experience a brief I/O suspension on your primary node as the snapshot occurs. The I/O suspension typically lasts on the order of one minute.

The read replicas are as easy to delete as they are to create; simply use the Amazon ElastiCache Management Console or call the DeleteCacheCluster API (specifying the CacheClusterIdentifier for the read replica you wish to delete).

Question 22

Q

Can I create both a primary and read replicas at the same time?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Yes. You can create a new cache cluster along with read replicas in minutes using the CreateReplicationGroup API or using the “Create” wizard at the Amazon ElastiCache Management Console and selecting “Multi-AZ Replication”. When creating the cluster, specify an identifier, the total number of desired shard in a cluster a read replicas per shard, along with cahe creation parameters such as node type, engine version, etc. You can also specify the Availability Zone for each shard in the cluster.

Question 23

Q

How do I connect to my read replica(s)?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

You can connect to a read replica just as you would connect to a primary cache node, using the DescribeCacheClusters API or AWS Management Console to retrieve the endpoint(s) for you read replica(s). If you have multiple read replicas, it is up to your application to determine how read traffic will be distributed amongst them.

Question 24

Q

How many read replicas can I create for a given primary node?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

At this time, Amazon ElastiCache allows you to create up to five (5) read replicas for a given primary node.

Question 25

Q

What happens to read replicas if failover occurs?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

In the event of a failover, any associated and available read replicas should automatically resume replication once failover has completed (acquiring updates from the newly promoted read replica).

Question 26

Q

Can I create a read replica of another read replica?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Creating a read replica of another read replica is not supported.

Question 27

Q

Can I promote my read replica into a “standalone” primary node?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

No, this is not supported. Instead, you may snapshot your ElastiCache for Redis node (you may select the primary or any of the read-replicas). You can then use the snapshot to seed a new ElastiCache for Redis primary.

Question 28

Q

Will my read replica be kept up-to-date with its primary node?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Updates to a primary node will automatically be replicated to any associated read replicas. However, with Redis’s asynchronous replication technology, a read replica can fall behind its primary cache node for a variety of reasons. Typical reasons include:

Write I/O volume to the primary cache node exceeds the rate at which changes can be applied to the read replica

Network partitions or latency between the primary cache node and a read replica

Read replicas are subject to the strengths and weaknesses of Redis replication. If you are using read replicas, you should be aware of the potential for lag between a read replica and its primary cache node, or “inconsistency”. You can monitor such lag potentially occuring via the “Replication Lag” CloudWatch metric, accessible through both the ElastiCache console and API, as well as those of the CloudWatch service.

Question 29

Q

How do I gain visibility into active read replica(s)?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

You can use the standard DescribeCacheClusters API to return a list of all the cache clusters you have deployed (including read replicas), or simply click on the “Redis” tab of the Amazon ElastiCache Management Console.

Amazon ElastiCache monitors the replication status of your read replicas and updates the Replication State field to Error if replication stops for any reason. You can review the details of the associated error thrown by the Redis engine by viewing the Replication Error field and take an appropriate action to recover from it. You can learn more about troubleshooting replication issues in the Troubleshooting a Read Replica problem section of the Amazon ElastiCache User Guide. If a replication error is fixed, the Replication State changes to Replicating.

Amazon ElastiCache allows you to gain visibility into how far a read replica has fallen behind its primary through the Amazon CloudWatch metric (“Replica Lag”) available via the AWS Management Console or Amazon CloudWatch APIs.

Question 30

Q

My read replica has fallen significantly behind its primary node. What should I do?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

As discussed in the previous questions, “inconsistency” or lag between a read replica and its primary node is common with Redis asynchronous replication. If an existing read replica has fallen too far behind to meet your requirements, you can reboot it. Keep in mind that replica lag may naturally grow and shrink over time, depending on your primary node’s steady-state usage pattern.

Question 31

Q

How do I delete a read replica? Will it be deleted automatically if its primary node is deleted?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

You can easily delete a read replica with a few clicks of the AWS Management Console or by passing its cache cluster identifier to the DeleteCacheCluster API. If you want to delete the read replica in addition to the primary cache node, you must use the DeleteReplicationGroup API or AWS Management Console.

Question 32

Q

How much do read replicas cost? When does billing begin and end?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

A read replica is billed as a standard node and at the same rates. Just like a standard node, the rate per “Node hour” for a read replica is determined by the node class of the read replica – please see Amazon ElastiCache detail page for up-to-date pricing. You are not charged for the data transfer incurred in replicating data between your primary cache node and read replica. Billing for a read replica begins as soon as the read replica has been successfully created (i.e. when status is listed as “active”). The read replica will continue being billed at standard Amazon ElastiCache cache node hour rates until you issue a command to delete it.

Question 33

Q

What happens during failover and how long does it take?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Initiated failover is supported by Amazon ElastiCache so that you can resume operations as quickly as possible. When failing over, Amazon ElastiCache simply flips the DNS record for your node to point at the read replica, which is in turn promoted to become the new primary. We encourage you to follow best practices and implement cache node connection retry at the application layer. Start-to-finish, failover typically completes within three to six minutes.

Question 34

Q

Can I create a read replica in another region as my primary?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

No. Your read replica may only be provisioned in the same or different Availability Zone of the same Region as your cache node primary.

Question 35

Q

Can I see which Availability Zone my primary is currently located in?

Read Replica

Amazon ElastiCache for Redis | Database

Answer

A

Yes, you can gain visibility into the location of the current primary by using the AWS Management Console or DescribeCacheClusters API.

After failover, my primary is now located in a different Availability Zone than my other AWS resources (e.g. EC2 instances).

Question 36

Q

Should I be concerned about latency?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Availability Zones are engineered to provide low latency network connectivity to other Availability Zones in the same Region. In addition, you may want to consider architecting your application and other AWS resources with redundancy across multiple Availability Zones so your application will be resilient in the event of an Availability Zone failure.

Question 37

Q

What is Multi-AZ for ElastiCache for Redis?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

An ElastiCache for Redis shard consists of a primary and up to five read replicas. Redis asynchronously replicates the data from the primary to the read replicas. During certain types of planned maintenance, or in the unlikely event of ElastiCache node failure or Availability Zone failure, Amazon ElastiCache will automatically detect the failure of a primary, select a read replica, and promote it to become the new primary. ElastiCache also propagates the DNS changes of the promoted read replica, so if your application is writing to the primary node endpoint, no endpoint change will be needed.

Question 38

Q

What are the benefits of using Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

The main benefits of running your ElastiCache for Redis in Multi-AZ mode are enhanced availability and smaller need for administration. If an ElastiCache for Redis primary node failure occurs, the impact on your ability to read/write to the primary is limited to the time it takes for automatic failover to complete. When Multi-AZ is enabled, ElastiCache node failover is automatic and requires no administration. You no longer need to monitor your Redis nodes and manually initiate a recovery in the event of a primary node disruption.

Question 39

Q

How does Multi-AZ work?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

You can use Multi-AZ if you are using ElastiCache for Redis and have a shard consisting of a primary node and one or more read replicas. If the primary node fails, ElastiCache will automatically detect the failure, select one from the available read replicas, and promote it to become the new primary. When cluster_mode parameter is disabled, ElastiCache will propagate the DNS changes of the promoted replica so that your application can keep writing to the primary endpoint. For cluster_mode enabled, ElastiCache will update the node map of the cluster. ElastiCache will also spin up a new node to replace the promoted read replica in the same Availability Zone of the failed primary. In case the primary failed due to temporary Availability Zone disruption, the new replica will be launched once that Availability Zone has recovered.

Question 40

Q

Can I have replicas in the same Availability Zone as the primary?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Yes. Note that placing both the primary and the replica(s) in the same Availability Zone will not make your ElastiCache for Redis replication group resilient to an Availability Zone disruption.

Question 41

Q

What events would cause Amazon ElastiCache to fail over to a read replica?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Amazon ElastiCache will failover to a read replica in the event of any of the following:

Loss of availability in primary’s Availability Zone

Loss of network connectivity to primary

Compute unit failure on primary

Question 42

Q

When should I use Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Using Redis replication in conjunction with Multi-AZ provides increased availability and fault tolerance. Such deployments are a natural fit for use in production environments. When running ElastiCache for Redis Cluster with cluster mode enabled, if your shards have one or more read replicas, Multi-AZ will automatically be enabled.

Question 43

Q

How do I create an ElastiCache for Redis replication group with Multi-AZ enabled?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

You can create an ElastiCache for Redis primary and read replicas by clicking “Create” on the ElastiCache Management Console. You can also do so by calling the CreateReplicationGroup API. For existing clusters (Redis 2.8.6, 2.8.19, 2.8.21, 2.8.22, 2.8.23, 2.8.24 and 3.2.4 with cluster_mode=disabled), you can enable Multi-AZ by choosing a cluster and clicking Modify on the ElastiCache Management Console or by using the ModifyReplicationGroup API. Switching a replication group to Multi-AZ is not disruptive to your Redis data and does not interfere your nodes’ ability to serve requests.

Question 44

Q

Which read replica will be promoted in case of primary node failure?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

If there are more than one read replicas, the read replica with the smallest asynchronous replication lag to the primary will be promoted.

Question 45

Q

How much does it cost to use Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Multi-AZ is free of charge. You only pay for the ElastiCache nodes that you use.

Question 46

Q

What are the performance implications of Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

ElastiCache currently uses the Redis engine’s native, asynchronous replication and is subject to its strengths and limitations. In particular, when a read replica connects to a primary for the first time, or if the primary changes, the read replica does a full synchronization of the data from the primary, imposing load on itself and the primary. For additional details regarding Redis replication please see here.

Question 47

Q

What node types support Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

All available node types in ElastiCache support Multi-AZ with one exception. When using Redis 2.8.x or Redis 3.x with cluster_mode=disabled, T2 family doesn’t support Multi-AZ.

Question 48

Q

Will I be alerted when automatic failover occurs?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Yes, Amazon ElastiCache will create an event to inform you that automatic failover occurred. You can use the DescribeEvents API to return information about events related to your ElastiCache node, or click the Events section of the ElastiCache Management Console.

Question 49

Q

After failover, my primary is now located in a different Availability Zone than my other AWS resources (for example, EC2 instances). Should I be concerned about latency?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

Availability Zones are engineered to provide low latency network connectivity to other Availability Zones in the same region. You may consider architecting your application and other AWS resources with redundancy across multiple Availability Zones so your application will be resilient in the event of an Availability Zone disruption.

Question 50

Q

Where can I get more information about Multi-AZ?

Multi-AZ

Amazon ElastiCache for Redis | Database

Answer

A

For more information about Multi-AZ, see ElastiCache documentation.

Question 51

Q

Can I test the Multi-AZ functionality?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Yes. If you have the “Multi-AZ” feature enabled on a cluster or replication group with one or more read replicas, you can trigger a failover. ElastiCache will respond in the same way as a real failure scenario – by detecting the failure, promoting the most up-to-date read replica to become the new primary, and then replacing the failed primary, attaching it as a new read replica in place of the one promoted. For more details on testing failover, please see documentation.

Question 52

Q

What is Backup and Restore?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Backup and Restore is a feature that allows customers to create snapshots of their ElastiCache for Redis clusters. ElastiCache stores the snapshots, allowing users to subsequently use them to restore Redis clusters.

Question 53

Q

What is a snapshot?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

A snapshot is a copy of your entire Redis cluster at a specific moment.

Question 54

Q

Why would I need snapshots?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Creating snapshots can be useful in case of data loss caused by node failure, as well as the unlikely event of a hardware failure. Another common reason to use backups is for archiving purposes. Snapshots are stored in Amazon S3, which is a durable storage, meaning that even a power failure won’t erase your data.

Question 55

Q

What can I do with a snapshot?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

You can use snapshots to warm start an ElastiCache for Redis cluster with preloaded data.

Question 56

Q

How does Backup and Restore work?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

When a backup is initiated, ElastiCache will take a snapshot of a specified Redis cluster that can later be used for recovery or archiving. You can initiate a backup anytime you choose or set a recurring daily backup with retention period of up to 35 days.

When you choose a snapshot to restore, a new ElastiCache for Redis cluster will be created and populated with the snapshot’s data. This way you can create multiple ElastiCache for Redis clusters from a specified snapshot.

Currently, ElastiCache uses Redis’ native mechanism to create and store an RDB file as the snapshot.

Question 57

Q

Where are my snapshots stored?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

The snapshots are stored in S3.

Question 58

Q

How can I get started using Backup and Restore?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

You can select to use the Backup and Restore feature through the AWS Management Console, through the ElastiCache APIs (CreateCacheCluster, ModifyCacheCluster and ModifyReplicationGroup API’s) and CLI. You can deactivate and reactivate the feature anytime you choose.

Question 59

Q

How do I specify which Redis cluster and node to backup?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Backup and Restore creates snapshots on a cluster basis. Users can specify which ElastiCache for Redis cluster to backup through the AWS Management Console, CLI or through the CreateSnapshot API. In a Replication Group, you can choose to backup the primary or any of the read-replica clusters. We recommend users enable backup on one of the read-replicas, mitigating any latency effect on the Redis primary.

Question 60

Q

Does ElastiCache for Memcached support Backup and Restore?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

No, snapshots are available only for ElastiCache for Redis.

Question 61

Q

How can I specify when a backup will take place?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Through the AWS Management Console, CLI or APIs you can specify when to start a single backup or a recurring backup. Users are able to:

Take a snapshot right now (through “Backup” console button in the “Redis” tab, or CreateSnapshot API)

Set up an automatic daily backup. The backup will take place during your preferred backup window. You can set that up through Creating/Modifying cluster via console or the CreateCacheCluster, ModifyCacheCluster or ModifyReplicationGroup API’s.

Question 62

Q

What is a backup window and why do I need it?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

The preferred backup window is the user-defined period of time during which your ElastiCache for Redis cluster backup will start. This is helpful if you want to backup at a certain time of day or to refrain from backups during a particularly high-utilization period.

Question 63

Q

What is the performance impact of taking a snapshot?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

While taking a snapshot, you may encounter increased latencies for a brief period at the node. Snapshots use Redis’s built-in BGSAVE and are subject to its strengths and limitations. In particular, the Redis process forks and the parent continues to serve requests while the child saves the data on disk and then exits. The forking increases the memory usage for the duration of the snapshot generation. When this memory usage exceeds that of the available memory of the node, swapping can get triggered, further slowing down the node. For this reason, we recommend generating snapshots on one of the read replicas (instead of the primary). Also, we suggest setting the reserved-memory parameter to minimize swap usage. See here for more details.

Question 64

Q

Can I create a snapshot from an ElastiCache for Redis read replica?

Backup and Restore

Amazon ElastiCache for Redis | Database

Answer

A

Yes. Creating a snapshot from a read replica is the best way to backup your data while minimizing performance impact.

Answer 63

A

Backup and Restore feature is available in all regions where ElastiCache service is available.

Answer 64

A

Yes. You can export your ElastiCache for Redis snapshots to an authorized S3 bucket in the same region as your cluster. For more details on exporting snapshots and setting the required permissions, please refer to this.

Answer 65

A

Yes. You must first copy your snapshot into an authorized S3 bucket of your choice in the same region and then use the S3 PUT object- Copy API to copy it to a bucket in another region. For more details on copying S3 objects, please see this.

Answer 66

A

Yes. You must first copy your snapshot into an authorized S3 bucket of your choice in the same region and then grant cross-account bucket permissions to the other account. For more details on S3 cross-account permissions, please see this. Finally, specify the S3 location of your RDB file during cluster creation through the Launch Cache Cluster Wizard in the console or through the CreateCacheCluster API.

Answer 67

A

Amazon ElastiCache provides storage space for one snapshot free of charge for each active ElastiCache for Redis cluster. Additional storage will be charged based on the space used by the snapshots with $0.085/GB every month (same price in all regions). Data transfer for using the snapshots is free of charge.

Answer 68

A

Retention period is the time span during which the automatic snapshots are retained. For example, if a retention period is set for 5, a snapshot that was taken today will be retained for 5 days before being deleted. You can choose to copy one or more automatic snapshots to store them as manual so that they won’t be deleted after the retention period is over.

Answer 69

A

You can use the AWS Management Console or ModifyCluster API to manage the period of time your automated backups are retained by modifying the RetentionPeriod parameter. If you desire to turn off automated backups altogether, you can do so by setting the retention period to 0 (not recommended).

Answer 70

A

When you delete an ElastiCache for Redis cluster, your manual snapshots are retained. You will also have an option to create a final snapshot before the cluster is deleted. Automatic snapshots are not retained.

Answer 71

A

All ElastiCache for Redis instance node types besides t1.micro and t2 family support backup and restore:

Current Generation Nodes:

cache. m3.medium
cache. m3.large
cache. m3.xlarge
cache. m3.2xlarge
cache. m4.large
cache. m4.xlarge
cache. m4.2xlarge
cache. m4.4xlarge
cache. m4.10xlarge
cache. r3.large
cache. r3.xlarge
cache. r3.2xlarge
cache. r3.4xlarge
cache. r3.8xlarge
cache. r4.large
cache. r4.xlarge
cache. r4.2xlarge
cache. r4.4xlarge
cache. r4.8xlarge
cache. r4.16xlarge

Previous Generation Nodes:

cache. m1.small
cache. m1.medium
cache. m1.large
cache. m1.xlarge
cache. m2.xlarge
cache. m2.2xlarge
cache. m2.4xlarge
cache. c1.xlarge

Answer 72

A

Yes. You can specify the S3 location of your RDB file during cluster creation through the “Create Cluster” Wizard in the console or through the CreateCacheCluster API.

Answer 73

A

ElastiCache for Redis Cluster allows customers to create and run managed Redis Clusters with multiple shards. It is compatible with open source Redis 3.2 and comes with a number of enhancements for a more stable and robust experience (see the “enhanced engine” section below for additional details on these enhancements).

Answer 74

A

There are three main scenarios for running a scale out Redis environment. First, if the total memory size of your Redis data exceeds or is projected to exceed the memory capacity of a single VM. Second, if the write throughput of your application to Redis exceeds the capacity of a single VM. Third, if you would like to spread the data across multiple shards so that any potential issue that comes up with a single node will have a smaller impact on the overall Redis environment.

Answer 75

A

Amazon ElastiCache provides a fully managed distributed in-memory Redis environment, from provisioning server resources to installing the engine software and applying any configuration parameters you choose. It uses enhancements to the Redis engine developed by Amazon, which results in a more robust and stable experience (see “enhanced engine” section for more details). Once your Redis environment is up and running, the service automates common administrative tasks such as failure detection and recovery, backups and software patching. It also provides a robust Multi-AZ solution with automatic failover. In case of a failure of one or more primary nodes in your cluster, Amazon ElastiCache will automatically detect the failure and respond by promoting the most up to date replica to primary. This process is automated and does not mandate any manual work on your behalf. Amazon ElastiCache also provides detailed monitoring metrics associated with your ElastiCache nodes, enabling you to diagnose and respond to issues very quickly.

Answer 76

A

Yes, Amazon ElastiCache for Redis Cluster is compatible with open source Redis 3.2. You can use the open source Redis Cluster clients to access scale-out clusters on ElastiCache for Redis.

Answer 77

A

Currently you cannot modify the number of shards in a cluster once it’s created.

Answer 78

A

If you are using Redis 3.2 with cluster_mode parameter disabled, you can simply choose the node or cluster you wish to upgrade and modify the engine version. ElastiCache will provision a Redis 3.2.4 cluster and migrate your data to it, while maintaining the endpoint.

If you are using Redis 3.2 with cluster_mode enabled, you can migrate to Redis Cluster by first creating a snapshot of your data using the backup and restore feature. Then, select the created snapshot and click on “Restore Snapshot” to create a Redis 3.2 cluster using the snapshotted data. Finally, update the new endpoint in your client. Note that to use Redis 3.2 in cluster mode you would need to switch to a Redis Cluster client.

Answer 79

A

No. Amazon ElastiCache for Redis provides the flexibility of clustered and non-clustered configuration at the same price. Customers can now enjoy enhanced engine functionality within Amazon ElastiCache for Redis and use full feature support for clustered configuration and scalability at the same price.

Answer 80

A

Each shard of an ElastiCache for Redis cluster consists of a primary and up to five read replicas. Redis asynchronously replicates the data from the primary to the read replicas. During certain types of planned maintenance, or in the unlikely event of ElastiCache node failure or Availability Zone failure, Amazon ElastiCache will automatically detect the failure of a primary, select a read-replica, and promote it to become the new primary.

ElastiCache for Redis Cluster provides enhancements and management for Redis 3.x environments. When running an unmanaged Redis environment, in a case of primary node failure, the cluster relies on a majority of masters to determine and execute a failover. If such majority doesn’t exist, the cluster will go into failed state, rejecting any further reads and writes. This could lead to major availability impact on the application, as well as requiring human intervention to manually salvage the cluster. ElastiCache for Redis Multi-AZ capability is built to handle any failover case for Redis Cluster with robustness and efficiency.

Answer 81

A

Redis 3.x works with intelligent clients that store a node map with all the cluster nodes’ endpoints. During a failover, the client updates the node map with the IP endpoint for the new primary. This provides up to 4x faster failover time than with ElastiCache for Redis 2.8.x.

Answer 82

A

You can use Multi-AZ if you are using an ElastiCache for Redis Cluster with each shard having 1 or more read-replicas. If a primary node of a shard fails, ElastiCache will automatically detect the failure, select one of the available read-replicas, and promote it to become the new primary. The Redis 3.x client will update the promoted replica as primary, no application change is required. ElastiCache will also spin up a new node to replace the promoted read-replica in the same Availability Zone of the failed primary. In case the primary failed due to a temporary Availability Zone failure, the new replica will be launched once that Availability Zone has recovered.

Answer 83

A

An ElastiCache for Redis Cluster backup is a series of snapshots of the cluster’s shards, stored together to keep a copy of your entire Redis data around a certain time frame.

Answer 84

A

Since a non-clustered ElastiCache for Redis environment has a single primary node, a backup is a single file which contains a copy of the Redis data. ElastiCache for Redis Cluster can have one or more shards, thus a backup might contain multiple files.

Answer 85

A

You cannot manually specify a node to backup within each shard. When initiating a backup, ElastiCache will automatically select the most up-to-date read replica in each shard and take a snapshot of its data.

Answer 86

A

When a backup is initiated, ElastiCache will take a backup of a specified cluster; that backup can later be used for recovery or archiving. The backup will include a copy of each of the cluster’s shards, thus a full backup contains a series of files. You can initiate a backup anytime you choose or set a recurring daily backup with retention period of up to 35 days.

When you choose a backup to restore, a new ElastiCache for Redis cluster will be created and populated with the backup’s data. Also, you can use this feature for an easy migration path to a managed Redis Cluster experience on ElastiCache. If you are running self-managed Redis on EC2, you can take RDB snapshots or your existing workloads (both Redis Cluster and single-shard Redis) and store them in S3. Then simply provide them as input for creating a sharded Redis Cluster on ElastiCache, and the desired number of shards. ElastiCache will do the rest.

Currently, ElastiCache uses Redis’ native mechanism to create and store an RDB file for each shard as the backup.

Answer 87

A

When you initiate a backup, ElastiCache will trigger backups of all of the shards of your cluster at the same time. In rare cases there might be a need to retake a snapshot of one or more nodes that did not complete successfully the first time. ElastiCache does that automatically and no user intervention is required. But in such a case, while each individual snapshot is a point-in-time representation of the node it was taken from, not all the cluster’s snapshots would be taken at the same time.

Answer 88

A

Through the AWS Management Console, CLI or APIs you can specify when to start a single backup or a recurring backup. Users are able to:

Take a backup right now (through “Create Snapshot” console button or CreateSnapshot API)

Set up an automatic daily backup. The backup will take place during your preferred backup window. You can set that up through Creating/Modifying cluster via console or the CreateReplicationGroup and ModifyReplicationGroup API’s.

Answer 89

A

Yes. You can specify the S3 location of your RDB files during cluster creation through the Create Cluster Wizard in the console or through the CreateReplicationGroup API. ElastiCache will automatically parse the Redis key-space of the RDB snapshot and redistribute it among the shards of the new cluster.

Answer 90

A

The engine within ElastiCache for Redis is fully compatible with open source Redis but also comes with enhancements that improve robustness and stability. Some of the enhancements are:

More usable memory: You can now safely allocate more memory for your application without risking increased swap usage during syncs and snapshots.

Improved synchronization: More robust synchronization under heavy load and when recovering from network disconnections. Additionally, syncs are faster as both the primary and replicas no longer use the disk for this operation.

Smoother failovers: In the event of a failover, your shard now recovers faster as replicas no longer flush their data to do a full re-sync with the primary.

Answer 91

A

To use the enhanced engine from the Amazon ElastiCache management console, just select an engine compatible with Redis engine version 2.8.22 or higher when creating a cluster. From that point on you will be using the enhanced engine. You can also use the enhanced engine through the ElastiCache API or AWS CLI by specifying the engine version when running the CreateCacheCluster API.

Answer 92

A

No. The enhanced engine is fully compatible with open-source Redis, thus you can enjoy its improved robustness and stability without the need to make any changes to your application code.

Answer 93

A

There is no additional charge for using the enhanced engine. As always, you will only be charged for the nodes you use.

Answer 94

A

Amazon ElastiCache for Redis provides the ability to add and remove shards from a running cluster. You can dynamically scale-out or scale-in your Redis cluster workloads to adapt to changes in demand. ElastiCache will resize the cluster by adding or removing shards and redistributing hash slots uniformly across the new shard configuration, all while the cluster continues to stay online and serve requests.

Answer 95

A

The ability to dynamically scale-out and scale-in a cluster can help you manage application variability and meet oscillating demands. You can right-size your clusters by adding or removing shards to scale performance and in-memory capacity. The feature eliminates the need to overprovision clusters based on peak demand, helps improve efficiency, and reduces cost.

Answer 96

A

Online Cluster Resizing is available with Redis engine version 3.2.10. To reshard your cluster, select the cluster and specify whether you want to add or remove shards. When you resize the cluster to scale-out, ElastiCache adds shards and migrates slots from existing shards to new shards, in a way such that the slots are uniformly distributed (by count) across shards. Similarly, when resizing the cluster to scale-in, ElastiCache migrates slots to the remaining shards to uniformly distribute the slots and deletes specified shards.

Answer 97

A

The time taken to resize a cluster depends on multiple factors, such as number of slots that need to be migrated across shards, size of data and incoming request rate on the cluster. However, the workflow is optimized to parallelize slot migration, which improves the time taken as you add more shards to scale out the cluster.

Answer 98

A

Yes, the cluster continues to stay online and serve incoming requests, while resharding is in progress. However, snapshotting a cluster while resharding is not supported to prevent increased load on the cluster.

Answer 99

A

While Online Cluster Resizing provides the benefits to scale out/in with zero downtime, it is a compute-intensive operation and can increase the latency of your client connection. To reduce the load on the cluster during the operation, we recommend that you follow the best practices (described in the documentation).

Answer 100

A

You can track the progress of the operation by watching the status of the cluster, shards and nodes. During the operation, the cluster, shards and nodes will stay in “modifying” status. Similarly, when shards are being created, deleted or participating in slot migration, the individual shard status will reflect these statuses to show progress. Additionally, the status of end-to-end operation can also be tracked using the progress indicator for the resharding operation, which indicates percentage completed and provides insight into the remaining time for the operation. Lastly, event messages indicate the progress by describing actions being taken (shard creation, slot migration, etc.) during this operation.

Answer 101

A

The rebalance operation can be used to redistribute slots amongst existing shards to achieve a uniform distribution. This is useful when a cluster is created with manually specified uneven slot distribution or a scale-out/in operation leaves the cluster with uneven distribution. Assuming the slots are identical in their memory and I/O requirements, uniform slot distribution by count is an easy way to load balance across shards.

Answer 102

A

When new nodes are added to scale-out a cluster, the nodes carry the same set of tags that are common across all existing nodes. Additionally, users can modify tags on all nodes and continue to use tagging as before.

Answer 103

A

No. The enhanced slot distribution used in cluster resizing workflow is compliant with Redis cluster client behavior and does not require any application changes. ElastiCache retains cluster endpoints, enabling you to continue using existing clients without any changes.

Answer 104

A

There is no additional charge for using the enhanced Redis engine. As always, you will only be charged for the nodes you use.

Answer 105

A

The encryption in-transit feature enables you to encrypt all communications between clients and Redis server as well as between the Redis servers (primary and read replica nodes).

Answer 106

A

Encryption at-rest allows for encryption of data during backups and restore - data backed up and restored on disk and via Amazon S3 is encrypted.

Answer 107

A

Encryption in-transit, encryption at-rest, and Redis AUTH are all opt-in features. At the time of Redis cluster creation via the console or command line interface, you can specify if you want to enable encryption and Redis AUTH and can proceed to provide an authentication token for communication with the Redis cluster. Once the cluster is setup with encryption enabled, ElastiCache seamlessly manages certificate expiration and renewal without requiring any additional action from the application. Additionally, the Redis clients need to support TLS to avail of the encrypted in-transit traffic.

Answer 108

A

No. Encryption in-transit requires clients to support TLS. Most of the popular Redis clients (such as Lettuce, Predis, go-Redis) provide support for TLS with some configuration settings. You have to make sure that your Redis client of choice is configured to support TLS and continue to use ElastiCache for Redis as before.

Answer 109

A

No. Encryption in-transit and encryption at-rest support is only available for new clusters and is not supported on existing ElastiCache for Redis clusters. ElastiCache for Redis version 3.2.6 is the initial version that supports these features.

Answer 110

A

No. ElastiCache manages certification expiration and renewal behind the scene. No user action is necessary for ongoing certificate maintenance.

Answer 111

A

No. Currently, ElastiCache does not provide the ability for you to use your certificates. ElastiCache manages certificates transparently for you.

Answer 112

A

All current generation instances are supported for encryption in transit and encryption at rest.

Answer 113

A

There are no additional costs for using encryption.

Answer 114

A

Yes, Amazon ElastiCache for Redis is a HIPAA Eligible Service and has been added to the AWS Business Associate Addendum (BAA). This means you can use ElastiCache for Redis to help you process, maintain, and store protected health information (PHI) and power healthcare applications.

Answer 115

A

If you have an executed Business Associate Agreement (BAA) with AWS, you can use ElastiCache for Redis to build HIPAA-compliant applications. If you do not have a BAA or have other questions about using AWS for your HIPAA-compliant applications, contact us for more information. See Architecting for HIPAA Security and Compliance on Amazon Web Services for information about how to configure Amazon HIPAA Eligible Services to store, process, and transmit PHI.

Answer 116

A

ElastiCache for Redis supports compliance programs such as SOC 1, SOC 2, SOC 3, ISO, MTCS, C5 and HIPAA. See AWS Services in Scope by Compliance Program for current list of supported complaince programs.

Brainscape's Knowledge GenomeTM

Database | Amazon ElastiCache for Redis Flashcards

Brainscape's Knowledge Genome^TM