Replacing nodes - Amazon ElastiCache
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Replacing nodes

Amazon ElastiCache for Memcached frequently upgrades its fleet with patches and upgrades being applied to instances seamlessly. However, from time to time we need to relaunch your ElastiCache for Memcached nodes to apply mandatory OS updates to the underlying host. These replacements are required to apply upgrades that strengthen security, reliability, and operational performance.

You have the option to manage these replacements yourself at any time before the scheduled node replacement window. When you manage a replacement yourself, your instance receives the OS update when you relaunch the node and your scheduled node replacement is canceled. You might continue to receive alerts indicating that the node replacement takes place. If you already manually mitigated the need for the maintenance, you can ignore these alerts.

Note

Replacement cache nodes automatically generated by Amazon ElastiCache may have different IP addresses. You are responsible for reviewing your application configuration to ensure that your cache nodes are associated with the appropriate IP addresses.

The following list identifies actions you can take when ElastiCache schedules one of your Memcached nodes for replacement.

  • Do nothing – If you do nothing, ElastiCache replaces the node as scheduled. When ElastiCache automatically replaces the node with a new node, the new node is initially empty.

  • Change your maintenance window – For scheduled maintenance events, you receive an email or a notification event from ElastiCache. In this case, if you change your maintenance window before the scheduled replacement time, your node now is replaced at the new time. For more information, see Modifying an ElastiCache cluster.

    Note

    The ability to change your replacement window by moving your maintenance window is only available when the ElastiCache notification includes a maintenance window. If the notification does not include a maintenance window, you cannot change your replacement window.

    For example, let's say it's Thursday, November 9, at 15:00 and the next maintenance window is Friday, November 10, at 17:00. Following are three scenarios with their outcomes:

    • You change your maintenance window to Fridays at 16:00, after the current date and time and before the next scheduled maintenance window. The node is replaced on Friday, November 10, at 16:00.

    • You change your maintenance window to Saturday at 16:00, after the current date and time and after the next scheduled maintenance window. The node is replaced on Saturday, November 11, at 16:00.

    • You change your maintenance window to Wednesday at 16:00, earlier in the week than the current date and time). The node is replaced next Wednesday, November 15, at 16:00.

    For instructions, see Managing maintenance.

  • Manually replace the node – If you need to replace the node before the next maintenance window, manually replace the node.

    If you manually replace the node, keys are redistributed. This redistribution causes cache misses.

    To manually replace a Memcached node

    1. Delete the node scheduled for replacement. For instructions, see Removing nodes from a cluster.

    2. Add a new node to the cluster. For instructions, see Adding nodes to a cluster.

    3. If you are not using auto discovery on this cluster, see your application and replace every instance of the old node's endpoint with the new node's endpoint.