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ElasticCache Replication

Links: 102 AWS DVA Index
Recommended Reads: ElastiCache

  • There are 2 types of ElastiCache replication
  • Cluster mode is just used for scaling writes.
    • If you want a fault tolerant multi AZ cheap solution we can use Cluster mode disable.
Both modes use asynchronous replication.

Cluster Mode: Disabled

  • One primary node and upto 5 replicas. There is only one shard.
    • attachments/Pasted image 20220514105722.jpg
  • Asynchronous Replication
  • The primary node is used for read/write whereas the other nodes are read-only.
  • One shard, all nodes have all the data
  • Multi-AZ enabled by default for failover
  • Useful for
    • Guarding against data loss if node failure
    • Helpful to scale read performance
All the nodes in a Redis cluster must reside in the same region.

Cluster Mode: Enabled

  • Data is partitioned across shards which is helpful for scaling writes.
    • attachments/Pasted image 20220514110232.jpg
  • Each shard has a primary and up to 5 replica nodes (similar to cluster mode disabled)
  • There is multi AZ capability.
  • Up to 500 nodes per cluster:
    • 500 shards with single master
    • 250 shards with master and replica. Since 250 x 2
    • 83 shards with one master and 5 replicas. Since 83 x 6 = 498
  • We CANNOT manually promote any of the replica nodes to primary.
If the cluster mentions high availability then go with cluster mode.

Last updated: 2023-02-15