Question 1

What's the difference between in-memory caching and a CDN?

Accepted Answer

In-memory caching stores data in RAM close to your application (often inside your VPC/VNet) and is great for database query results, sessions, and computed objects. A CDN caches content at edge locations near users and is best for static files (images, CSS, JS) and cacheable HTTP responses. Many architectures use both: CDN for edge delivery and in-memory cache for application/data-layer speed.

Question 2

When should I use in-memory caching?

Accepted Answer

Use it when you have repeated reads of the same data, expensive database queries, or computed results that can be reused (product details, user profiles, feature flags, rate limits, session data). It’s especially helpful when database CPU/IO is a bottleneck or when you need sub-millisecond to low-millisecond access times. Avoid caching data that changes constantly unless you have a clear invalidation strategy.

Question 3

How much does in-memory caching cost?

Accepted Answer

Cost depends on (1) cache engine (Redis/Memcached), (2) node size and count (RAM/CPU), (3) high availability (replicas, multi-AZ/zone), (4) network data transfer, and (5) backups/persistence features (for Redis). Managed services typically charge per node-hour (or similar) plus storage/backup where applicable. The biggest driver is usually the amount of RAM you provision to hold your working set with headroom.

In-Memory Caching

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