Cost Optimization - Database

Question 1

RDS - Pricing points

Answer 1

• Instance type and size
• Database storage
• Data transfer out between AZs and between regions
• Backup storage

Question 2

RDS - Instance types

Answer 2

• General purpose: good balance between memory and network resources
• Burstable performance: offer a baseline level of CPU with the ability to surpass that baseline
• Memory optimized: designed for memory-intensive database workload

Question 3

RDS - Storage options

Answer 3

• General purpose SSD: default choice that offers balance for many uses cases. Provides a baseline of 3 IOPS / GiB
• Provisioned IOPS SSD: suitable for I/O-intensive database workloads. Can provision up to 256,000 IOPS
• Magnetic: cheapest storage, not recommended for new deployments

Question 4

RDS - Instance payment options

Answer 4

• On-demand: pay as you go, no upfront payments
• Reserved instances: 1 or 3 year commitment. Up to 69% savings

Question 5

RDS - Read replicas

Answer 5

• Offer asynchronous replication. It’s highly scalable
• Used for read scaling. Can be within the same or different AZ / Region
• Can be manually promoted to a standalone database instance, or a Multi-AZ instance
• When promoted to a Multi-AZ instance, it will be independent of whether the source database is a Multi-AZ instance too. It’s like an active-pasive deployment

Question 6

RDS - Multi-AZ deployments

Answer 6

• Offer synchronous replication. It’s highly durable
• Primary instance is only active
• There’s automatic failover to standby when a problem is detected
• Automatic backups are taken from standby

Question 7

DynamoDB - On-demand mode request units

Answer 7

• Write request unit (WRU): equivalent to one write of a 1KB item
• Read request units (RRU): represents one strongly consistent read request, or one-half eventually consistent read request for a 4KB item. Transactional read requests require two RRUs to read a 4KB item
• The number of reads for transactional read requests depends on the consistency model chosen (strong or eventual)

Question 8

DynamoDB - Provisioned mode capacity units

Answer 8

• Write capacity unit (WCU): equivalent to one write per second of a 1KB item
• Read capacity units (RCU): represents one strongly consistent read per second, or up to two eventually consistent reads per second for a 4KB item. Transactional read requests require two RCUs to do one read per second for a 4KB item
• The number of reads for transactional read requests depends on the consistency model chosen (strong or eventual)

Question 9

DynamoDB - Pricing points

Answer 9

• Always charged for data stored at a per GB-month rate
• Can purchase RCUs and WCUs with a 1 or 2 year commitment at a reduced rate
• On provisioned mode, if more reads and / or writes are needed:
• DynamoDB will throttle your connections until it drops reads and writes, or
• You can purchase more capacity units to be allocated
• Have additional costs:
• Global secondary indexes and Global DynamoDB tables will need their own capacity units
• DynamoDB backups