claude-mods/skills/nginx-ops/SKILL.md

---

name: nginx-ops description: "Nginx configuration, reverse proxy, SSL/TLS, load balancing, and performance tuning. Use for: nginx, reverse proxy, load balancer, proxy_pass, ssl certificate, lets encrypt, web server, location block, upstream, server block, nginx config, certbot, hsts, gzip, rate limiting." license: MIT allowed-tools: "Read Write Bash" metadata: author: claude-mods

related-skills: docker-ops, security-ops, ci-cd-ops

Nginx Operations

Comprehensive Nginx configuration, reverse proxy patterns, SSL/TLS hardening, load balancing strategies, and performance optimization for production deployments.

---

Configuration Architecture Quick Reference

nginx.conf (main context)
├── worker_processes auto;
├── worker_rlimit_nofile 65535;
│
├── events {                          # Connection handling
│   ├── worker_connections 4096;
│   └── multi_accept on;
│   }
│
├── http {                            # HTTP server settings
│   ├── include mime.types;
│   ├── default_type application/octet-stream;
│   ├── sendfile on;
│   ├── gzip on;
│   │
│   ├── upstream backend {            # Load balancing pool
│   │   └── server 127.0.0.1:3000;
│   │   }
│   │
│   ├── server {                      # Virtual host
│   │   ├── listen 443 ssl;
│   │   ├── server_name example.com;
│   │   │
│   │   ├── location / {              # Request routing
│   │   │   └── proxy_pass http://backend;
│   │   │   }
│   │   │
│   │   └── location /static/ {
│   │       └── root /var/www;
│   │       }
│   │   }
│   │
│   └── include /etc/nginx/conf.d/*.conf;
│   }
│
└── stream {                          # TCP/UDP proxying (optional)
    └── server { ... }
    }

Directive Inheritance Rules

Rule	Behavior	Example
Inherit down	Child blocks inherit parent directives	gzip on; in http applies to all server blocks
Override	Child directive overrides parent	gzip off; in location overrides http-level gzip on;
Array directives	NOT inherited - must be redeclared	proxy_set_header in location replaces ALL headers from server
No upward	Inner blocks never affect outer	location-level settings don't affect server

Critical: Array-type directives (proxy_set_header, add_header, proxy_hide_header) are completely replaced when redefined in a child block, not merged. If you set one proxy_set_header in a location, you must redeclare ALL of them.

---

Reverse Proxy Decision Tree

Need to proxy requests?
│
├─ Single backend server?
│  └─ Use simple proxy_pass
│     proxy_pass http://127.0.0.1:3000;
│
├─ Multiple backend servers?
│  │
│  ├─ Need session persistence?
│  │  ├─ By client IP → ip_hash
│  │  └─ By cookie    → sticky cookie (Nginx Plus)
│  │
│  ├─ Backends have unequal capacity?
│  │  └─ Use weight parameter
│  │     server backend1:3000 weight=3;
│  │     server backend2:3000 weight=1;
│  │
│  ├─ Want fewest active connections?
│  │  └─ least_conn
│  │
│  ├─ Want even random distribution?
│  │  └─ random two least_conn
│  │
│  └─ Default (no special needs)?
│     └─ round-robin (default, no directive needed)
│
├─ WebSocket connections?
│  └─ Add Upgrade + Connection headers
│     proxy_set_header Upgrade $http_upgrade;
│     proxy_set_header Connection "upgrade";
│
├─ gRPC backend?
│  └─ Use grpc_pass grpc://backend;
│
└─ Streaming / Server-Sent Events?
   └─ Disable buffering
      proxy_buffering off;

---

SSL/TLS Quick Start

Let's Encrypt with Certbot

# Install certbot
sudo apt install certbot python3-certbot-nginx   # Debian/Ubuntu
sudo dnf install certbot python3-certbot-nginx    # RHEL/Fedora

# Obtain certificate (nginx plugin - easiest)
sudo certbot --nginx -d example.com -d www.example.com

# Obtain certificate (webroot - no nginx restart)
sudo certbot certonly --webroot -w /var/www/html -d example.com

# Test auto-renewal
sudo certbot renew --dry-run

Minimal Production SSL Config

server {
    listen 443 ssl http2;
    server_name example.com;

    # Certificates
    ssl_certificate     /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    # Modern TLS (1.2 + 1.3)
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384;
    ssl_prefer_server_ciphers off;

    # HSTS (2 years)
    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;

    # OCSP Stapling
    ssl_stapling on;
    ssl_stapling_verify on;
    ssl_trusted_certificate /etc/letsencrypt/live/example.com/chain.pem;
    resolver 1.1.1.1 8.8.8.8 valid=300s;
    resolver_timeout 5s;

    # Session caching
    ssl_session_cache shared:SSL:10m;
    ssl_session_timeout 1d;
    ssl_session_tickets off;

    root /var/www/example.com;
    index index.html;
}

# HTTP → HTTPS redirect
server {
    listen 80;
    server_name example.com www.example.com;
    return 301 https://example.com$request_uri;
}

---

Location Matching Order

Nginx evaluates location blocks in a specific priority order, not in the order they appear in the config file.

Priority	Modifier	Type	Example	Behavior
1	=	Exact match	location = /favicon.ico	Stops search immediately on match
2	^~	Prefix (no regex)	location ^~ /static/	Stops search if this prefix matches (skips regex)
3	~	Regex (case-sensitive)	location ~ \.php$	First matching regex wins
3	~*	Regex (case-insensitive)	location ~* \.(jpg\|png)$	First matching regex wins
4	(none)	Prefix	location /api/	Longest prefix wins (but only after regex check)

Evaluation Algorithm

1. Check all prefix locations, remember the longest match
2. If longest match has ^~ modifier → use it, stop
3. Check regex locations in config-file order → first match wins
4. If no regex matches → use the longest prefix from step 1
5. = /path is checked first and wins immediately if matched

Example

location = /             { }  # Only exact "/"
location /               { }  # Catch-all prefix
location /api/           { }  # Prefix: /api/*
location ^~ /static/     { }  # Prefix, skip regex: /static/*
location ~ \.php$        { }  # Regex: any .php file
location ~* \.(gif|jpg)$ { }  # Case-insensitive regex: images

Request URI	Matched Location	Why
/	= /	Exact match (priority 1)
/index.html	/	Longest prefix, no regex match
/api/users	/api/	Longest prefix, no regex match
/static/logo.png	^~ /static/	^~ skips regex check
/app/index.php	~ \.php$	Regex beats prefix
/photos/cat.jpg	~* \.(gif\|jpg)$	Regex beats prefix

---

Common Configurations

SPA Routing (React, Vue, Angular)

server {
    listen 80;
    server_name app.example.com;

    root /var/www/app/dist;
    index index.html;

    # Serve static files directly, fall back to index.html for SPA routes
    location / {
        try_files $uri $uri/ /index.html;
    }

    # Cache static assets aggressively
    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff2?)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }
}

WebSocket Proxy

location /ws/ {
    proxy_pass http://127.0.0.1:3000;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_read_timeout 86400s;  # Keep WebSocket alive for 24h
    proxy_send_timeout 86400s;
}

Rate Limiting

# Define zone: 10MB shared memory, 10 requests/second per IP
limit_req_zone $binary_remote_addr zone=api:10m rate=10r/s;

server {
    location /api/ {
        # Allow burst of 20, process excess without delay up to burst
        limit_req zone=api burst=20 nodelay;
        limit_req_status 429;

        proxy_pass http://backend;
    }
}

Gzip Compression

http {
    gzip on;
    gzip_comp_level 5;          # Balance CPU vs compression (1-9)
    gzip_min_length 256;        # Don't compress tiny responses
    gzip_vary on;               # Vary: Accept-Encoding header
    gzip_proxied any;           # Compress proxied responses too
    gzip_types
        text/plain
        text/css
        text/javascript
        application/javascript
        application/json
        application/xml
        application/xml+rss
        image/svg+xml;
}

Static File Serving

location /static/ {
    alias /var/www/static/;     # Note: alias, not root (includes /static/ path)
    expires 30d;
    add_header Cache-Control "public, no-transform";

    # Disable access log for static files
    access_log off;

    # Enable open file cache
    open_file_cache max=1000 inactive=20s;
    open_file_cache_valid 30s;
    open_file_cache_min_uses 2;
}

CORS Headers

location /api/ {
    # CORS headers
    add_header Access-Control-Allow-Origin "https://app.example.com" always;
    add_header Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS" always;
    add_header Access-Control-Allow-Headers "Authorization, Content-Type" always;
    add_header Access-Control-Max-Age 86400 always;

    # Handle preflight requests
    if ($request_method = OPTIONS) {
        return 204;
    }

    proxy_pass http://backend;
}

---

Docker Patterns

Nginx as Reverse Proxy in Docker Compose

# docker-compose.yml
services:
  nginx:
    image: nginx:alpine
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./certs:/etc/nginx/certs:ro
    depends_on:
      - app
    networks:
      - webnet

  app:
    build: .
    expose:
      - "3000"    # Internal only, not published to host
    networks:
      - webnet

networks:
  webnet:

# nginx.conf for docker-compose (use service name as hostname)
upstream app_backend {
    server app:3000;    # Docker DNS resolves service name
}

server {
    listen 80;
    location / {
        proxy_pass http://app_backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Multi-Stage Build with Static Assets

# Stage 1: Build frontend
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Serve with nginx
FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html
COPY nginx.conf /etc/nginx/conf.d/default.conf
EXPOSE 80

# nginx.conf for containerized SPA
server {
    listen 80;
    root /usr/share/nginx/html;
    index index.html;

    # SPA routing
    location / {
        try_files $uri $uri/ /index.html;
    }

    # Health check endpoint
    location /health {
        access_log off;
        return 200 "OK\n";
        add_header Content-Type text/plain;
    }

    # Cache busted assets
    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff2?)$ {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }
}

---

Common Gotchas

Gotcha	Why	Fix
Trailing slash in proxy_pass	proxy_pass http://backend keeps /api/users as-is; proxy_pass http://backend/ strips the matched location prefix	Be intentional: with / to strip prefix, without to preserve
Missing proxy headers	Backend sees nginx's IP, not the client's. Breaks auth, logging, and geo detection	Always set X-Real-IP, X-Forwarded-For, X-Forwarded-Proto, and Host
Buffer size errors (502)	Large headers (cookies, JWTs) exceed default buffer sizes	Increase proxy_buffer_size 8k; and proxy_buffers 4 16k;
worker_connections too low	Default is 512 or 1024; each client uses 2 connections (client + upstream)	Set worker_connections 4096; and raise worker_rlimit_nofile
try_files with proxy_pass	try_files and proxy_pass in the same location don't work as expected	Use try_files $uri @backend; with a named location for proxy
"if is evil"	if inside location creates an implicit nested location, breaking directives	Use map for variable-based logic; reserve if for return/rewrite only
Resolver for dynamic upstreams	Variables in proxy_pass (e.g., $upstream) bypass startup DNS resolution	Add resolver 127.0.0.11 valid=30s; (Docker) or resolver 1.1.1.1;
Missing index directive	Returns 403 Forbidden when accessing a directory instead of index file	Add index index.html; in server or location block
Permission denied on socket	Nginx worker can't read the upstream Unix socket	Ensure nginx user is in the socket's group; chmod 660 the socket
Duplicate Content-Encoding with gzip	Upstream already compresses + nginx gzip double-compresses	Use gzip_proxied carefully or proxy_set_header Accept-Encoding "";
add_header not inherited	Adding ANY add_header in a location discards ALL parent add_header directives	Redeclare all headers in the child block, or use include for shared headers
alias vs root confusion	root appends the location path; alias replaces it. /img/ + root /data = /data/img/; alias /data/ = /data/	Use alias when location path shouldn't appear in filesystem path

---

Reference Files

File	Contents	Lines
reverse-proxy.md	Upstream blocks, load balancing, proxy caching, WebSocket/gRPC, timeouts, real-world configs	~650
ssl-security.md	TLS config, Let's Encrypt, HSTS, OCSP, security headers, rate limiting, mTLS	~550
performance.md	Worker tuning, compression, caching, HTTP/2+3, static files, monitoring	~550

---

See Also

• docker-ops - Container orchestration, docker-compose patterns
• security-ops - Application security, authentication patterns
• ci-cd-ops - Deployment pipelines, zero-downtime deploys
• Nginx official docs
• Mozilla SSL Configuration Generator
• Nginx Config Generator