RedisとMemcached：適切なエンジンの選択

Amazon ElastiCache とは

Memcached：シンプルさを追求

# Create a Memcached cluster with 3 nodes
aws elasticache create-cache-cluster \
  --cache-cluster-id my-memcached \
  --engine memcached \
  --cache-node-type cache.r7g.large \
  --num-cache-nodes 3 \
  --cache-subnet-group-name my-subnet-group

# Memcached auto-discovers nodes via the config endpoint
# Application connects to: my-memcached.cfg.use1.cache.amazonaws.com:11211

Redis：高機能なインメモリストア

# Redis data structure examples

# String
# SET user:1:name 'Alice'
# GET user:1:name

# Hash (object-like)
# HSET product:42 name 'Widget' price '9.99' stock '100'
# HGETALL product:42

# Sorted set (leaderboard)
# ZADD leaderboard 9500 'alice' 8700 'bob' 9100 'carol'
# ZREVRANGE leaderboard 0 2 WITHSCORES

# Pub/Sub
# PUBLISH notifications 'order_shipped:12345'
# SUBSCRIBE notifications

Redis の永続化：AOF と RDB

# Create an ElastiCache Redis cluster with AOF enabled
aws elasticache create-replication-group \
  --replication-group-id my-redis \
  --replication-group-description 'Redis with persistence' \
  --cache-node-type cache.r7g.large \
  --engine redis \
  --num-cache-clusters 2 \
  --cache-parameter-group-name default.redis7 \
  --snapshot-retention-limit 5

# Note: Enable AOF via parameter group: appendonly=yes

Redis のレプリケーションと自動フェイルオーバー

# Create a Redis replication group with Multi-AZ failover
aws elasticache create-replication-group \
  --replication-group-id prod-redis \
  --description 'Production Redis with HA' \
  --cache-node-type cache.r7g.xlarge \
  --engine redis \
  --multi-az-enabled \
  --automatic-failover-enabled \
  --num-cache-clusters 3 \
  --cache-subnet-group-name multi-az-subnet-group

# 1 primary + 2 replicas across 3 AZs

リーダーボードに使う Redis のソート済みセット

# Leaderboard operations using Redis sorted sets

# Add/update scores
# ZADD game:leaderboard 10500 'player:alice'
# ZADD game:leaderboard 9800  'player:bob'
# ZADD game:leaderboard 11200 'player:carol'

# Get top 3 players (highest scores first)
# ZREVRANGE game:leaderboard 0 2 WITHSCORES
# Result: carol 11200, alice 10500, bob 9800

# Get a player's rank (0-indexed)
# ZREVRANK game:leaderboard 'player:alice'
# Result: 1 (second place)

メッセージングに使う Redis Pub/Sub

# Publisher side (broadcasts to 'notifications' channel)
# PUBLISH notifications '{"type":"order_shipped","orderId":"12345"}'

# Subscriber side (listens for messages)
# SUBSCRIBE notifications

# Pattern subscribe (wildcard channel matching)
# PSUBSCRIBE order:*
# Receives messages from: order:created, order:shipped, order:delivered

# Note: Unlike SQS, pub/sub is fire-and-forget — no acknowledgement

Memcached と Redis：選択表

キャッシュノードのタイプとファミリー

# Get available cache node types
aws elasticache describe-cache-engine-versions \
  --engine redis \
  --query 'CacheEngineVersions[?contains(EngineVersion, '7')].{Engine:Engine,Version:EngineVersion}'

# Check memory and vCPU for a node type
aws elasticache describe-cache-engine-versions \
  --cache-parameter-group-family redis7

# Monitor evictions to detect memory pressure
# CloudWatch: Evictions metric > 0 means cache is full

ElastiCache のセキュリティ

# Create a Redis cluster with TLS and AUTH token
aws elasticache create-replication-group \
  --replication-group-id secure-redis \
  --description 'Encrypted Redis' \
  --cache-node-type cache.r7g.large \
  --engine redis \
  --transit-encryption-enabled \
  --at-rest-encryption-enabled \
  --auth-token 'MySecretPassword123!'

# Store the AUTH token in Secrets Manager, not in your app code

エビクションポリシー

# Set eviction policy via parameter group
aws elasticache create-cache-parameter-group \
  --cache-parameter-group-name redis7-lru \
  --cache-parameter-group-family redis7 \
  --description 'LRU eviction policy'

aws elasticache modify-cache-parameter-group \
  --cache-parameter-group-name redis7-lru \
  --parameter-name-values ParameterName=maxmemory-policy,ParameterValue=allkeys-lru

# Apply the parameter group to your cluster:
aws elasticache modify-replication-group \
  --replication-group-id prod-redis \
  --cache-parameter-group-name redis7-lru

クイックチェック

レッスンのまとめ