Monitoring ElastiCache

Question 1

4 Monitoring attributes

Answer 1

• CPU Attributes
• Swap Usage
• Evictions
• Concurrent Connections

Question 2

True or False: Memcached is multithreaded

Answer 2

True

Question 3

Memcached maximum CPU load

Answer 3

90%. Must add addtional nodes to the cluster if this is exceeded.

Question 4

Is Redis multi-threaded?

Answer 4

No.

Question 5

How do you determine when to scale Redis?

Answer 5

90 / # of cores in an instance. Ex: 90 / 4 = 22.5%

Question 6

What is swap usage?

Answer 6

The amount of swap file that is being used.

Question 7

What is the typical size of a swap file?

Answer 7

Equal to the amount of RAM. Ex: 4GB RAM = 4GB swap file.

Question 8

What is a swap file?

Answer 8

A reserve of hard drive space allocated for “swapping” actively processing information, for inactive information.

Question 9

Why is a swap file used?

Answer 9

If there is not enough RAM for all processes, an OS can use swap file to store in memory data for later processing. This comes with performance degredation.

Question 10

What is a healthy SwapUsage metric? (Not to be confused with status)

Answer 10

Average of 0Mb, not to exceed 50Mb.

Question 11

If SwapUsage exceeds 50Mb, how should this be addressed?

Answer 11

Increase the memcached_connections_overhead parameter.

Question 12

what is memcached_connections_overhead

Answer 12

It is the amount of memory reserved for memcached connections.

Question 13

True or False, to get Redis Swap usage information, review the reserved-memory metric.

Answer 13

True: SwapUsage is for memcached. Redis uses the reserved-memory metric.

Question 14

What are Evictions?

Answer 14

It is the removal of old cached items to make room for new cached items.

Question 15

Evictions Settings for memcached

Answer 15

There are not recommended settings. Choose a threashold base on the application needs.

Question 16

Evictions Scaling for memcached

Answer 16

Scale up, or scale out

Question 17

Evictions Settings for Redis

Answer 17

No recommended settings. Choose a threshold based on application needs.

Question 18

Evictions Scaling for Redis

Answer 18

Can only scale out by adding read replicas. No scaling up options.

Question 19

True or False: You cannot scale up a Redis instance?

Answer 19

True. Redis can only scale out by adding read replicas.

Question 20

Settings for Concurrent Connections - Memcached and Redis

Answer 20

No recommended settings

Question 21

Reasons for spike in concurrent connections in Redis or Memcached

Answer 21

• Either sustained spike in number of connections

- Application is not releasing connections as it should.