ElastiCache

✅ What is ElastiCache?

AWS ElastiCache is a fully managed, in-memory data store service for Redis and Memcached, used to speed up applications by caching frequent queries or data.

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🚀 Benefits

• ⚡ Ultra-low latency (microseconds)

• 🔁 Redis clustering and failover

• 🛡️ Secure (IAM, VPC, encryption)

• 📈 Auto-backup and monitoring

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🔄 Supported Engines

Engine	Use Case
Redis	Caching, Pub/Sub, Sessions
Memcached	Lightweight, no persistence

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📊 Architecture (Redis Example)

                   +-------------------------+
                   |     Application Tier    |
                   | (EC2 / Lambda / ECS / EKS) 
                   +-----------+-------------+
                               |
                               v
                    +----------------------+
                    |   ElastiCache Proxy  | (Optional)
                    +----------------------+
                               |
                     +----------------------+
                     |   ElastiCache Redis  |
                     |----------------------|
                     |  Primary Node        |
                     |  + Replica Nodes     |
                     +----------------------+
                               |
                 Auto failover & replication (if enabled)

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🔁 Workflow

1. 🏃 App sends read/write request to Redis endpoint

2. 🔍 If data exists in Redis → return (cache hit)

3. ❌ If not → fetch from DB, then store in Redis (cache miss)

4. 🔁 Optional: Replicas handle read traffic

5. 🔄 TTL expires or is invalidated when updated in DB

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🔐 High Availability (Redis Only)

• Multi-AZ replication

• Automatic failover to replica node

• Cluster mode (sharding) for scalability

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🔧 Common Use Cases

• ✅ API/data caching (e.g., product details)

• ✅ Session storage (web apps)

• ✅ Leaderboards (gaming)

• ✅ Real-time metrics (IoT, dashboards)

• ✅ Pub/Sub systems

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🛠️ Sample Terraform (Redis)

resource "aws_elasticache_subnet_group" "example" {
  name       = "example-subnet"
  subnet_ids = ["subnet-123", "subnet-456"]
}

resource "aws_elasticache_replication_group" "redis" {
  replication_group_id          = "my-redis-group"
  replication_group_description = "Redis HA"
  node_type                     = "cache.t3.micro"
  number_cache_clusters         = 2
  engine                        = "redis"
  automatic_failover_enabled    = true
  subnet_group_name             = aws_elasticache_subnet_group.example.name
}

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