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 values. A CDN caches static or cacheable HTTP content (images, JS/CSS, sometimes HTML) at edge locations near users. Many systems use both: CDN for web assets and in-memory cache for application/data-layer acceleration.

Question 2

When should I use in-memory caching?

Accepted Answer

Use it when you have repeated reads of the same data, database load is high, or latency needs to be very low. Common fits include product catalogs, user profiles, session storage, rate limiting, feature flags, and caching expensive computations. It’s especially helpful when your database is the bottleneck or when traffic is spiky and you need a buffer to absorb bursts.

Question 3

How much does in-memory caching cost?

Accepted Answer

Cost depends mainly on (1) memory size and node count, (2) instance/node type, (3) replication and multi-AZ/zone features, (4) network data transfer, and (5) backups/snapshots (for Redis). Managed services typically charge per node-hour plus storage for backups (if enabled). Self-managed caching on VMs shifts cost to compute, operations time, and reliability engineering.

In-Memory Caching

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