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I'm setting up a new microservice and planning to use aws api gateway as the front door. For those who've used it, what were the unexpected hurdles or costs you ran into that aren't in the docs?

Yep, the big surprises are the numbers you don’t see in the initial docs. Caching in aws api gateway can blow up the monthly bill if you have a lot of reads. Data transfer out to the internet or across regions also adds up faster than you expect. If your backend is Lambda, you’ll see both invocation costs and some extra data transfer between aws api gateway and Lambda. Build a lightweight cost model up front and keep an eye on the cost dashboard; roll the scope back if you need to.

Endpoint type choice trips people up. HTTP API is cheaper and simpler and handles a lot of typical needs, but REST offers more complex features and OpenAPI specification import is slick in some setups. If you want a lot of compatibility with older tooling or deeper request/response mapping, REST might be worth the extra cost, otherwise HTTP API is usually enough. aws api gateway

Auth is another trap. AWS Cognito or a Lambda authorizer adds latency and a separate cost. Cache authorizer results where you can and test for cold starts at scale.

Timeouts and backend reliability. If your upstream calls sometimes hang longer than the gateway timeout, you’ll need to redesign flow, perhaps with asynchronous steps or a queue. The 29 second integration timeout is a real constraint. aws api gateway

Security edges: think about staging vs prod, least privilege, and seeing WAF costs if you turn that on. Also DNS with a custom domain and TLS certs via ACM can surprise if you forget renewal costs or cache invalidation.

Deployment and observability: make sure you have a sane CI/CD around API definitions, stage variables, and proper logging. API gateway logs cost money; you’ll want to trim or archive; use CloudWatch alarms to catch spikes. aws api gateway

Performance note: use caching strategically and consider choosing between edge vs regional endpoints based on your users. The learner path is starting with HTTP API, a Lambda backend, and adding Cognito or other authorizers later if needed.