Amazon ElastiCache Well-Architected Lens Operational Excellence Pillar - Amazon ElastiCache
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Amazon ElastiCache Well-Architected Lens Operational Excellence Pillar

The operational excellence pillar focuses on running and monitoring systems to deliver business value, and continually improving processes and procedures. Key topics include automating changes, responding to events, and defining standards to manage daily operations.

OE 1: How do you understand and respond to alerts and events triggered by your ElastiCache cluster?

Question-level introduction: When you operate ElastiCache clusters you can optionally receive notifications and alerts when specific events occur. ElastiCache, by default, logs events that relate to your resources, such as a failover, node replacement, scaling operation, scheduled maintenance, and more. Each event includes the date and time, the source name and source type, and a description.

Question-level benefit: Being able to understand and manage the underlying reasons behind the events that trigger alerts generated by your cluster enables you to operate more effectively and respond to events appropriately.

  • [Required] Review the events generated by ElastiCache on the ElastiCache console (after selecting your region) or using the Amazon Command Line Interface (Amazon CLI) describe-events command and the ElastiCache API. Configure ElastiCache to send notifications for important cluster events using Amazon Simple Notification Service (Amazon SNS). Using Amazon SNS with your clusters allows you to programmatically take actions upon ElastiCache events.

    • There are two large categories of events: current and scheduled events. The list of current events includes: resource creation and deletion, scaling operations, failover, node reboot, snapshot created, cluster’s parameter modification, CA certificate renewal, failure events (cluster provisioning failure - VPC or ENI-, scaling failures - ENI-, and snapshot failures). The list of scheduled events includes: node scheduled for replacement during the maintenance window and node replacement rescheduled.

    • Although you may not need to react immediately to some of these events, it is critical to first look at all failure events:

      • ElastiCache:AddCacheNodeFailed

      • ElastiCache:CacheClusterProvisioningFailed

      • ElastiCache:CacheClusterScalingFailed

      • ElastiCache:CacheNodesRebooted

      • ElastiCache:SnapshotFailed (Redis only)

    • [Resources]:

  • [Best] To automate responses to events, leverage Amazon products and services capabilities such as SNS and Lambda Functions. Follow best practices by making small, frequent, reversible changes, as code to evolve your operations over time. You should use Amazon CloudWatch metrics to monitor your clusters.

    [Resources]: Monitor Amazon ElastiCache for Redis (cluster mode disabled) read replica endpoints using Amazon Lambda, Amazon Route 53, and Amazon SNS for a use case that uses Lambda and SNS.

OE 2: When and how do you scale your existing ElastiCache clusters?

Question-level introduction: Right-sizing your ElastiCache cluster is a balancing act that needs to be evaluated every time there are changes to the underlying workload types. Your objective is to operate with the right sized environment for your workload.

Question-level benefit: Over-utilization of your resources may result in elevated latency and overall decreased performance. Under-utilization, on the other hand, may result in over-provisioned resources at non-optimal cost optimization. By right-sizing your environments you can strike a balance between performance efficiency and cost optimization. To remediate over or under utilization of your resources, ElastiCache can scale in two dimensions. You can scale vertically by increasing or decreasing node capacity. You can also scale horizontally by adding and removing nodes.

OE 3: How do you manage your ElastiCache cluster resources and maintain your cluster up-to-date?

Question-level introduction: When operating at scale, it is essential that you are able to pinpoint and identify all your ElastiCache resources. When rolling out new application features you need to create cluster version symmetry across all your ElastiCache environment types: dev, testing, and production. Resource attributes allow you to separate environments for different operational objectives, such as when rolling out new features and enabling new security mechanisms.

Question-level benefit: Separating your development, testing, and production environments is best operational practice. It is also best practice that your clusters and nodes across environments have the latest software patches applied using well understood and documented processes. Taking advantage of native ElastiCache features enables your engineering team to focus on meeting business objectives and not on ElastiCache maintenance.

  • [Best] Run on the latest engine version available and apply the Self-Service Updates as quickly as they become available. ElastiCache automatically updates its underlying infrastructure during your specified maintenance window of the cluster. However, the nodes running in your clusters are updated via Self-Service Updates. These updates can be of two types: security patches or minor software updates. Ensure you understand the difference between types of patches and when they are applied.


  • [Best] Organize your ElastiCache resources using tags. Use tags on replication groups and not on individual nodes. You can configure tags to be displayed when you query resources and you can use tags to perform searches and apply filters. You should use Resource Groups to easily create and maintain collections of resources that share common sets of tags.


OE 4: How do you manage clients’ connections to your ElastiCache clusters?

Question-level introduction: When operating at scale you need to understand how your clients connect with the ElastiCache cluster to manage your application operational aspects (such as response times).

Question-level benefit: Choosing the most appropriate connection mechanism ensures that your application does not disconnect due to connectivity errors, such as time-outs.

  • [Required] Separate read from write operations and connect to the replica nodes to execute read operations. However, be aware when you separate the writes from the reads you will lose the ability to read a key immediately after writing it due to the asynchronous nature of Redis replication. The WAIT command can be leveraged to improve real world data safety and force replicas to acknowledge writes before responding to clients, at an overall performance cost. Using replica nodes for read operations can be configured in your ElastiCache for Redis client library using the ElastiCache reader endpoint for cluster mode disabled. For cluster mode enabled, use the ElastiCache for Redis READONLY command. For many of the ElastiCache for Redis client libraries, ElastiCache for Redis READONLY is implemented by default or via a configuration setting.


  • [Required] Use connection pooling. Establishing a TCP connection has a cost in CPU time on both client and server sides and pooling allows you to reuse the TCP connection.

    To reduce connection overhead, you should use connection pooling. With a pool of connections your application can re-use and release connections ‘at will’, without the cost of establishing the connection. You can implement connection pooling via your ElastiCache for Redis client library (if supported), with a Framework available for your application environment, or build it from the ground up.

  • [Best] Ensure that the socket timeout of the client is set to at least one second (vs. the typical “none” default in several clients).

    • Setting the timeout value too low can lead to possible timeouts when the server load is high. Setting it too high can result in your application taking a long time to detect connection issues.

    • Control the volume of new connections by implementing connection pooling in your client application. This reduces latency and CPU utilization needed to open and close connections, and perform a TLS handshake if TLS is enabled on the cluster.

    [Resources]: Configure Amazon ElastiCache for Redis for higher availability

  • [Good] Using pipelining (when your use cases allow it) can significantly boost the performance.

    • With pipelining you reduce the Round-Trip Time (RTT) between your application clients and the cluster and new requests can be processed even if the client has not yet read the previous responses.

    • With pipelining you can send multiple commands to the server without waiting for replies/ack. The downside of pipelining is that when you eventually fetch all the responses in bulk there may have been an error that you will not catch until the end.

    • Implement methods to retry requests when an error is returned that omits the bad request.

    [Resources]: Pipelining

OE 5: How do you deploy ElastiCache Components for a Workload?

Question-level introduction: ElastiCache environments can be deployed manually through the Amazon Console, or programmatically through APIs, CLI, toolkits, etc. Operational Excellence best practices suggest automating deployments through code whenever possible. Additionally, ElastiCache clusters can either be isolated by workload or combined for cost optimization purposes.

Question-level benefit: Choosing the most appropriate deployment mechanism for your ElastiCache environments can improve Operation Excellence over time. It is recommended to perform operations as code whenever possible to minimize human error and increase repeatability, flexibility, and response time to events.

By understanding the workload isolation requirements, you can choose to have dedicated ElastiCache environments per workload or combine multiple workloads into single clusters, or combinations thereof. Understanding the tradeoffs can help strike a balance between Operational Excellence and Cost Optimization

  • [Required] Understand the deployment options available to ElastiCache, and automate these procedures whenever possible. Possible avenues of automation include CloudFormation, Amazon CLI/SDK, and APIs.


  • [Required] For all workloads determine the level of cluster isolation needed.

    • [Best]: High Isolation – a 1:1 workload to cluster mapping. Allows for finest grained control over access, sizing, scaling, and management of ElastiCache resources on a per workload basis.

    • [Better]: Medium Isolation – M:1 isolated by purpose but perhaps shared across multiple workloads (for example a cluster dedicated to caching workloads, and another dedicated for messaging).

    • [Good]: Low Isolation – M:1 all purpose, fully shared. Recommended for workloads where shared access is acceptable.

OE 6: How do you plan for and mitigate failures?

Question-level introduction: Operational Excellence includes anticipating failures by performing regular "pre-mortem" exercises to identify potential sources of failure so they can be removed or mitigated. ElastiCache offers a Failover API that allows for simulated node failure events, for testing purposes.

Question-level benefit: By testing failure scenarios ahead of time you can learn how they impact your workload. This allows for safe testing of response procedures and their effectiveness, as well as gets your team familiar with their execution.

[Required] Regularly perform failover testing in dev/test accounts. TestFailover

OE 7: How do you troubleshoot Redis engine events?

Question-level introduction: Operational Excellence requires the ability to investigate both service-level and engine-level information to analyze the health and status of your clusters. Amazon ElastiCache for Redis can emit Redis engine logs to both Amazon CloudWatch and Amazon Kinesis Data Firehose.

Question-level benefit: Enabling Redis engine logs on Amazon ElastiCache for Redis clusters provides insight into events that impact the health and performance of clusters. Redis engine logs provide data directly from the Redis engine that is not available through the ElastiCache events mechanism. Through careful observation of both ElastiCache events (see preceding OE-1) and Redis engine logs, it is possible to determine an order of events when troubleshooting from both the ElastiCache service perspective and Redis engine perspective.

  • [Required] Ensure that Redis engine logging functionality is enabled, which is available as of ElastiCache for Redis 6.2 and newer. This can be performed during cluster creation or by modifying the cluster after creation.

    • Determine whether Amazon CloudWatch Logs or Amazon Kinesis Data Firehose is the appropriate target for Redis engine logs.

    • Select an appropriate target log within either CloudWatch or Kinesis Data Firehose to persist the logs. If you have multiple clusters, consider a different target log for each cluster as this will help isolate data when troubleshooting.


  • [Best] If using Amazon CloudWatch Logs, consider leveraging Amazon CloudWatch Logs Insights to query Redis engine log for important information.

    As an example, create a query against the CloudWatch Log group that contains the Redis engine logs that will return events with a LogLevel of ‘WARNING’, such as:

    fields @timestamp, LogLevel, Message | sort @timestamp desc | filter LogLevel = "WARNING"

    [Resources]:Analyzing log data with CloudWatch Logs Insights