DNS Is Not a Load Balancer#

This needs to be said upfront: DNS was designed for name resolution, not traffic management. Using DNS for failover is a pragmatic hack that works well enough for most use cases, but it has fundamental limitations.

DNS responses are cached at multiple levels (recursive resolvers, OS caches, application caches, browser caches). You cannot force a client to re-resolve. You can set a TTL, but clients and resolvers are free to ignore it (and some do). Java applications, for example, cache DNS indefinitely by default in some JVM versions unless you explicitly set networkaddress.cache.ttl.

API Gateway Patterns#

An API gateway sits between clients and your backend services. It handles cross-cutting concerns – authentication, rate limiting, request transformation, routing – so your services do not have to. Choosing the right gateway and configuring it correctly is one of the first decisions in any microservices architecture.

Gateway Responsibilities#

Before selecting a gateway, clarify which responsibilities it should own:

• Routing – directing requests to the correct backend service based on path, headers, or method.
• Authentication and authorization – validating tokens, API keys, or certificates before requests reach backends.
• Rate limiting – protecting backends from traffic spikes and enforcing usage quotas.
• Request/response transformation – modifying headers, rewriting paths, converting between formats.
• Load balancing – distributing traffic across service instances.
• Observability – emitting metrics, logs, and traces for every request that passes through.
• TLS termination – handling HTTPS so backends can speak plain HTTP internally.

No gateway does everything equally well. The right choice depends on which of these responsibilities matter most in your environment.

CDN and Edge Computing Patterns#

A CDN (Content Delivery Network) caches content at edge locations close to users, reducing latency and offloading traffic from origin servers. Edge computing extends this by running custom code at those edge locations, enabling request transformation, authentication, A/B testing, and dynamic content generation without round-tripping to an origin server.

CDN Cache Fundamentals#

Cache-Control Headers#

The origin server controls CDN caching behavior through HTTP headers. Getting these right is the single most impactful CDN optimization.