---
name: nginx
description: Use this skill when helping with Nginx or OpenResty/Lua development tasks. Triggers include writing or debugging Nginx configuration (server blocks, location blocks, upstreams, proxy_pass, rewrites, maps, try_files), OpenResty/Lua module development (content handlers, access control, header manipulation, shared dictionaries, cosocket usage), and Nginx performance tuning (buffer sizing, keepalive tuning, caching, connection pooling, benchmarking). Also use when the user mentions .conf files, nginx.conf, lua modules in the context of a web server/reverse proxy/CDN, or any directive-level Nginx questions. Do NOT use for Apache, Caddy, HAProxy, or general web server questions unrelated to Nginx.
license: MIT
metadata:
  author: Nejc Lovrencic
  version: "1.0"
---

# Nginx & OpenResty Development

## Core Guidance

When writing or reviewing Nginx configuration:

1. Always consider the **directive inheritance model**. Child blocks inherit from parent unless they redefine the directive. For example, adding one `proxy_set_header` in a location block wipes all inherited `proxy_set_header` directives from the server block.
2. Prefer `map` over `if` for conditional logic. `if` in location context is dangerous and only reliably supports `return` and `rewrite`. See references/nginx-gotchas.md for the full list.
3. Always clarify `proxy_pass` trailing-slash behavior — it is the single most common source of subtle bugs.
4. When writing `upstream` blocks, always include keepalive configuration and explain connection pooling implications.
5. When writing Nginx directives, always check [docs](https://nginx.org/en/docs/), specifically module references, to verify that a directive actually exists, and what values it accepts (on/off, variable, fixed values, etc).

When writing OpenResty/Lua code:

1. Always check **phase restrictions** before using cosocket or subrequest APIs. See references/openresty-api.md.
2. Prefer `ngx.ctx` over `ngx.var` for passing data between phases because it's more performant.
3. Avoid using ngx.var multiple times for the same variable, as it's less performant than accessing Lua variable.
4. Use `ngx.timer.at` for background/async work, never block the event loop.

When advising on performance:

1. Consult references/testing-patterns.md for benchmarking methodology.
2. Always consider the full request path: client → Nginx → upstream, and tune each segment.
3. Buffer sizing has cascading effects — refer to the buffer tuning section in references/nginx-gotchas.md.

## Reference Files

Load these as needed based on the task:

- **[references/nginx-gotchas.md](references/nginx-gotchas.md)** — Directive behavior gotchas, inheritance rules, location matching, common misconfigurations. Read when writing or debugging any Nginx config.
- **[references/openresty-api.md](references/openresty-api.md)** — Phase handler reference, shared dict operations. Read when writing Lua/OpenResty code.
- **[references/testing-patterns.md](references/testing-patterns.md)** — Config validation. Read when testing or benchmarking.