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March 03, 2025 00:49
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Caddy Web Server Cheatsheet

A quick reference guide to the Caddy web server, covering its configuration syntax, common directives, and usage examples.

Caddyfile Basics

Caddyfile Structure

A Caddyfile defines the configuration for one or more sites.

  • Site Addresses: The starting point for each site definition.
  • Directives: Instructions for how Caddy should handle requests to that site.
  • Blocks: Group directives together to apply them conditionally or configure sub-features.

Caddyfile is case-insensitive.
Whitespace is generally ignored.

Site Addresses

example.com

Matches requests to example.com.

example.com:8080

Matches requests to example.com on port 8080.

*.example.com

Matches requests to any subdomain of example.com.

http://example.com

Matches HTTP requests to example.com (usually redirects to HTTPS).

https://example.com

Matches HTTPS requests to example.com.

localhost

Matches requests to localhost.

Basic Directives

root * /var/www

Sets the root directory for serving files.

file_server

Enables the file server to serve static files.

encode gzip

Enables Gzip compression for responses.

log

Configures logging.

tls self_signed

Uses a self-signed certificate for TLS (not recommended for production).

reverse_proxy localhost:9000

Proxies requests to a backend server.

Common Directives

Redirection

redir /old /new

Redirects /old to /new.

redir /old /new 301

Permanent redirect (301 status code).

redir /old https://example.com/new 302

Temporary redirect (302 status code) to a different domain.

redir /.well-known/acme-challenge/* https://acme-staging.example.com{path}

Redirects ACME challenge requests to a staging server.

Error Handling

handle_errors { respond "An error occurred" 500 }

Handles errors and returns a 500 error with a custom message.

handle_errors { reverse_proxy localhost:9000 }

Proxies error requests to another server.

handle_errors { rewrite /error.html file_server }

Serves a custom error page.

Header Manipulation

header { Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" }

Sets the Strict-Transport-Security header for HTTPS.

header -Server

Removes the Server header.

header /api/* { Access-Control-Allow-Origin "*" }

Sets CORS headers for the /api/* path.

header +X-Custom-Header "Custom Value"

Adds a custom header

Advanced Configuration

Reverse Proxy

reverse_proxy /api/* localhost:8080 - Proxies requests to /api/* to a backend server on localhost:8080.

reverse_proxy https://backend.example.com { header_up Host {host} header_up X-Real-IP {remote_host} } - Proxies requests to another domain, preserving the original host and client IP.

reverse_proxy /metrics 192.168.1.10:9100 - Proxies to an internal ip address

Load Balancing

reverse_proxy localhost:8080 localhost:8081

Basic load balancing between two backend servers.

reverse_proxy { to localhost:8080 localhost:8081 policy round_robin }

Load balancing with a specific policy (round_robin, first, random, least_conn, header).

reverse_proxy { to 192.168.1.10:8080 192.168.1.11:8080 health_uri /healthz health_interval 10s }

Configures health checks for backend servers.

TLS Configuration

tls internal

Uses Caddy’s internal CA for issuing certificates (for development).

tls { dns cloudflare <API_TOKEN> }

Uses Cloudflare DNS for ACME DNS challenge.

tls /path/to/cert.pem /path/to/key.pem

Specifies the paths to a custom certificate and key.

tls { protocols tls1.2 tls1.3 }

Specifies the TLS protocol versions.

Caddy CLI

Basic Commands

caddy version

Displays the Caddy version.

caddy start

Starts Caddy in the background.

caddy stop

Stops Caddy.

caddy reload

Reloads the Caddy configuration without downtime.

caddy adapt

Converts a Caddyfile to JSON configuration.

Configuration Management

caddy file-server

Starts a simple file server.

caddy run

Starts Caddy in the foreground (useful for debugging).

caddy environ

Prints Caddy’s environment variables.

Service Management (systemd)

Caddy can be managed as a systemd service. Ensure the Caddyfile is in the correct location (e.g., /etc/caddy/Caddyfile).

sudo systemctl start caddy - Starts the Caddy service.

sudo systemctl stop caddy - Stops the Caddy service.

sudo systemctl reload caddy - Reloads the Caddy configuration.

sudo systemctl status caddy - Checks the status of the Caddy service.