What it is: A managed in-memory caching service (Redis or Memcached).

What it’s for:

• Reduce database load and speed up responses.
• Store session data, frequently accessed data, leaderboards.

Key ideas:

• Two engines:
  • Redis
  • Memcached
• Cache is typically used in front of RDS/DynamoDB.

Exam cues:

• “reduce read load on DB” → ElastiCache.
• “millisecond response for repeated reads” → caching.

Hard words:

• *in-memory* /ɪn ˈmeməri/: trong RAM
• *caching* /ˈkæʃɪŋ/: lưu đệm