Question: How can you implement horizontal scaling in ElastiCache?

Answer

Horizontal scaling in Amazon ElastiCache involves increasing the number of cache nodes to handle more requests or data. This is often referred to as sharding, and it allows for linear scalability by distributing data across multiple nodes.

In ElastiCache, you have two primary options for implementing horizontal scaling:

1. Adding additional nodes: You can add additional nodes to your ElastiCache cluster using either the AWS Management Console, the AWS CLI, or the AWS SDKs. When you add a node, ElastiCache automatically rebalances your data among the existing and new nodes.

Here's an example using the AWS CLI:

aws elasticache modify-replication-group --replication-group-id my-replication-group --num-cache-clusters 6

This command would scale out a replication group named "my-replication-group" to six cache clusters.

2. Using partitioning or sharding: Depending on the engine (like Redis), you can split data across multiple nodes manually. For example, Redis (cluster mode enabled) offers automatic sharding, allowing you to partition your data across up to 500 shards.

Remember to monitor performance after scaling to ensure that your new configuration adequately handles your workload. In addition, be aware that while horizontal scaling can increase capacity and throughput, it may also introduce latency due to network overhead between nodes, so consider this when planning your scaling strategy.