AWS ElastiCache vs MemoryDB: Which One Do You Actually Need?

Source: Dev.to

Decision guide

Is your data ephemeral (can be regenerated or lost)?

• YES → Use ElastiCache (≈ $12 / month for cache.t4g.micro)
• NO → Use MemoryDB (≈ $25 +/ month, durable storage)

That’s the whole decision.

Why I chose ElastiCache for jo4.io

I need Redis for:

Since all of these are ephemeral, ElastiCache is the appropriate choice.

When to consider MemoryDB

MemoryDB is suited for scenarios where Redis holds the source of truth:

• Leaderboards / rankings that cannot be recalculated
• Real‑time inventory where Redis is the database
• Session data you can’t afford to lose (e.g., financial applications)
• Message queues where lost messages mean lost transactions

MemoryDB benefits

• Multi‑AZ durability (data survives node failures)
• Transaction log durability (writes are persisted)
• Point‑in‑time recovery

Cost comparison (small production workload)

MemoryDB does not offer a micro tier, so its minimum cost is higher.

Example: Terraform for an ElastiCache cluster

resource "aws_elasticache_cluster" "redis" {
  cluster_id           = "jo4-prod-redis"
  engine               = "redis"
  engine_version       = "7.1"
  node_type            = "cache.t4g.micro"
  num_cache_nodes      = 1
  port                 = 6379
  parameter_group_name = "default.redis7"

  subnet_group_name    = aws_elasticache_subnet_group.redis.name
  security_group_ids   = [aws_security_group.redis.id]

  # Daily snapshot, 7‑day retention (even for ephemeral data)
  snapshot_retention_limit = 7
  snapshot_window          = "02:00-03:00"
  maintenance_window       = "sun:03:00-sun:04:00"
}

One advantage of ElastiCache: no authentication is required when accessed from within your VPC.

Example: Spring Boot Redis configuration (YAML)

spring:
  data:
    redis:
      host: ${REDIS_HOST}
      port: ${REDIS_PORT}
      timeout: 5000
      # No password needed – security group controls access

Comparison with Redis Cloud

Migration tips (Redis Cloud → ElastiCache)

1. Update connection settings: host, port, and remove auth.
2. Accept that the cache starts empty – design your app to handle empty caches gracefully.
3. For rate limiting and caching, the migration is trivial because the data is ephemeral.

Use‑case matrix

Bottom line

• ElastiCache: Fast, cheap, ideal for caching and rate limiting where data loss is acceptable.
• MemoryDB: Durable, more expensive, for cases where Redis is the primary data store.

Don’t overthink it. If you can regenerate the data, go with ElastiCache.