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title: "Concepts"
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# Concepts

These pages explain how ngx_mruby runs Ruby inside nginx: where in the
processing of a request each handler runs, how the filters see a response,
how a handler waits without blocking the worker, and what lives across
requests.

- [Request phases](/concepts/request-phases/): nginx's HTTP phases in order, and
  the ngx_mruby directive that runs Ruby in each of them.
- [Filters](/concepts/filters/): where the header filter and the body filter of
  ngx_mruby stand in nginx's filter chains, and what each one receives.
- [Waiting without blocking](/concepts/async/): how `Nginx::Async.sleep` and
  `Nginx::Async::HTTP.sub_request` give the worker back to nginx.
- [Lifetimes](/concepts/lifetimes/): one `mrb_state` per worker, and what a worker
  keeps between requests.
- [Trust boundary](/security/trust-boundary/): what ngx_mruby trusts,
  what it treats as client input, and what a script is responsible for.