Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

Which Metrics Should I Monitor?

The following CloudWatch metrics offer good insight into ElastiCache performance. In most cases, we recommend that you set CloudWatch alarms for these metrics so that you can take corrective action before performance issues occur.

CPUUtilization

This is a host-level metric reported as a percentage. For more information, see Host-Level Metrics.

For smaller node types with 2vCPUs or less, use the CPUUtilization metric to monitor your workload.

Generally speaking, we suggest you set your threshold at 90% of your available CPU. Because Redis is single-threaded, the actual threshold value should be calculated as a fraction of the node's total capacity. For example, suppose you are using a node type that has two cores. In this case, the threshold for CPUUtilization would be 90/2, or 45%.

You will need to determine your own threshold, based on the number of cores in the cache node that you are using. If you exceed this threshold, and your main workload is from read requests, scale your cache cluster out by adding read replicas. If the main workload is from write requests, depending on your cluster configuration, we recommend that you:

For larger node types with 4vCPUs or more, you may want to use the EngineCPUUtilization metric, which reports the percentage of usage on the Redis engine core. To see if this metric is available on your nodes and for more information, see Metrics for Redis.

EngineCPUUtilization

For larger node types with 4vCPUs or more, you may want to use the EngineCPUUtilization metric, which reports the percentage of usage on the Redis engine core. To see if this metric is available on your nodes and for more information, see Metrics for Redis.

For more information, see the CPUs section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

SwapUsage

This is a host-level metric reported in bytes. For more information, see Host-Level Metrics.

The FreeableMemory CloudWatch metric being close to 0 (i.e., below 100MB) or SwapUsage metric greater than the FreeableMemory metric indicates a node is under memory pressure. If this happens, see the following topics:

Evictions

This is a cache engine metric. We recommend that you determine your own alarm threshold for this metric based on your application needs.

CurrConnections

This is a cache engine metric. We recommend that you determine your own alarm threshold for this metric based on your application needs.

An increasing number of CurrConnections might indicate a problem with your application; you will need to investigate the application behavior to address this issue.

For more information, see the Connections section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

Memory

Memory is a core aspect of Redis. Understanding the memory utilization of your cluster is necessary to avoid data loss and accommodate future growth of your dataset. Statistics about the memory utilization of a node are available in the memory section of the Redis INFO command.

For more information, see the Memory section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

Network

One of the determining factors for the network bandwidth capacity of your cluster is the node type you have selected. For more information about the network capacity of your node, see Amazon ElastiCache pricing.

For more information, see the Network section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

Latency

You can measure a command’s latency with a set of CloudWatch metrics that provide aggregated latencies per data structure. These latency metrics are calculated using the commandstats statistic from the Redis INFO command.

For more information, see the Latency section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

Replication

The volume of data being replicated is visible via the ReplicationBytes metric. Although this metric is representative of the write load on the replication group, it doesn't provide insights into replication health. For this purpose, you can use the ReplicationLag metric.

For more information, see the Replication section at Monitoring best practices with Amazon ElastiCache for Redis using Amazon CloudWatch.

Traffic Management

ElastiCache for Redis automatically manages traffic against a node when more incoming commands are sent to the node than can be processed by Redis. This is done to maintain optimal operation and stability of the engine.

When traffic is actively managed on a node, the metric TrafficManagementActive will emit data points of 1. This indicates that the node may be underscaled for the workload being provided. If this metric remains 1 for long periods of time, evaluate the cluster to decide if scaling up or scaling out is necessary.

For more information, see the TrafficManagementActive metric on the Metrics page.