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AWS Services - ElastiCache

Overview

Amazon ElastiCache is a fully managed, in-memory caching service that supports Redis and Memcached.
It improves application performance by retrieving data from fast, managed in-memory caches, instead of relying solely on slower disk-based databases.

Use cases:

  • Caching frequently accessed data (e.g., session data, user profiles).
  • Real-time analytics.
  • Pub/Sub messaging (Redis).
  • Leaderboards, gaming applications.
  • Distributed caching layer for web apps and microservices.

Engine Options

Redis

  • In-memory key-value store with persistence support.
  • Advanced features: replication, clustering, pub/sub, transactions.
  • Supports data structures like strings, lists, sets, hashes, and sorted sets.
  • Best for: caching, real-time analytics, leaderboards, queues.

Memcached

  • Simple, high-performance in-memory object cache.
  • No persistence or advanced data types.
  • Easier to scale horizontally.
  • Best for: object caching, database query caching, session stores.

Key Concepts

  • Cluster: A collection of cache nodes.
  • Node: A single cache instance.
  • Replication Group (Redis only): Primary/replica setup for high availability.
  • Shards (Redis only): Partitioning data across multiple nodes.
  • Parameter Groups: Configure engine-specific settings.
  • Security Groups / VPC: Control access to the cache cluster.

Setting up ElastiCache from AWS Console

  1. Go to ElastiCache in the AWS Management Console.
  2. Select engine: Redis or Memcached.
  3. Configure:
    • Cluster name.
    • Engine version.
    • Node type (memory/CPU).
    • Number of nodes (and shards for Redis).
    • Multi-AZ replication for high availability.
    • Subnet group and security groups (VPC required).
  4. Enable automatic backups (Redis only).
  5. Launch cluster.

Connecting to ElastiCache

From an EC2 instance in the same VPC:

  1. Ensure the EC2 security group allows outbound access and ElastiCache security group allows inbound on port:
    • Redis: 6379
    • Memcached: 11211
  2. Use native client libraries:
    • redis-cli for Redis
    • memcached-tool or any Memcached client library

Example: Using Redis with Telnet

You can test connectivity and basic commands using telnet.

telnet <elasticache-endpoint> 6379

Commands:

SET mykey "HelloWorld"
+OK

GET mykey
"HelloWorld"

If connection works, this confirms the cache cluster is up and responding.

Example: Using Memcached with Telnet

telnet <elasticache-endpoint> 11211

Commands:

set mykey 0 900 5
hello
STORED

get mykey
VALUE mykey 0 5
hello
END

Monitoring & Management

  • Amazon CloudWatch Metrics:
    • CPUUtilization
    • FreeableMemory
    • Evictions
    • CurrConnections
  • Events: Notifications about cluster/node changes.
  • Backups (Redis only): Snapshots to S3.
  • Parameter Groups: Tune engine configuration.
  • Maintenance Windows: Apply patches automatically.

High Availability & Scaling

  • Replication Groups (Redis): Primary + multiple replicas across AZs.
  • Auto-failover: If the primary fails, a replica is promoted.
  • Cluster Mode Enabled (Redis): Sharded architecture for horizontal scaling.
  • Scaling:
    • Vertically: Change node type to larger instance.
    • Horizontally: Add shards or replicas.

Best Practices

  • Place ElastiCache in the same VPC and subnet as your application for low latency.
  • Use Redis AUTH or VPC security groups for access control.
  • Enable Multi-AZ with automatic failover for production workloads.
  • Use parameter groups to fine-tune performance.
  • For session storage, set appropriate TTL (time-to-live) values.
  • Regularly monitor evictions and memory usage.

Useful CLI Commands

Check Redis connection:

redis-cli -h <endpoint> -p 6379 ping

Check Memcached stats:

echo stats | nc <endpoint> 11211

Summary

  • ElastiCache boosts performance by caching frequently accessed data.
  • Choose Redis for advanced features and persistence, or Memcached for simple caching.
  • Use CloudWatch for monitoring, snapshots for Redis backups, and multi-AZ for high availability.
  • Test connectivity via telnet, redis-cli, or nc.