Caddyfile Tutorial

This tutorial will teach you the basics of the HTTP Caddyfile so that you can quickly and easily produce good-looking, functional site configs.

Objectives:

🔲 First site
🔲 Static file server
🔲 Templates
🔲 Compression
🔲 Multiple sites
🔲 Matchers
🔲 Environment variables
🔲 Comments

Prerequisites:

Basic terminal / command line skills
Basic text editor skills
caddy in your PATH

Create a new text file named Caddyfile (no extension).

The first thing you should type is your site's address:

localhost

Then hit enter and type what you want it to do. For this tutorial, make your Caddyfile look like this:

localhost

respond "Hello, world!"

Save that and run Caddy (since this is a training tutorial, we'll use the --watch flag so changes to our Caddyfile are applied automatically):

caddy run --watch

The first time, you'll be asked for your password. This is so Caddy can serve your site over HTTPS.

Open localhost in your browser and see your web server working, complete with HTTPS!

That's not particularly exciting, so let's change our static response to a file server with directory listings enabled:

localhost

file_server browse

Save your Caddyfile, then refresh your browser tab. You should either see a list of files or an HTML page if there is an index file in the current directory.

Adding functionality

Let's do something interesting with our file server: serve a templated page. Create a new file and paste this into it:

<!DOCTYPE html>
<html>
	<head>
		<title>Caddy tutorial</title>
	</head>
	<body>
		Page loaded at: {{now | date "Mon Jan 2 15:04:05 MST 2006"}}
	</body>
</html>

Save this as caddy.html in the current directory and load it in your browser: https://localhost/caddy.html

The output is:

Page loaded at: {{now | date "Mon Jan 2 15:04:05 MST 2006"}}

Wait a minute. We should see today's date. Why didn't it work? It's because the server hasn't yet been configured to evaluate templates! Easy to fix, just add a line to the Caddyfile so it looks like this:

localhost

templates
file_server browse

Save that, then reload the browser tab. You should see:

Page loaded at: Thu Nov 21 10:20:02 UTC 2024

With Caddy's templates module, you can do a lot of useful things with static files, such as including other HTML files, making sub-requests, setting response headers, working with data structures, and more!

It's good practice to compress responses with a quick and modern compression algorithm. Let's enable Gzip and Zstandard support using the encode directive:

localhost

encode zstd gzip
templates
file_server browse

That's the basic process for getting a semi-advanced, production-ready site up and running!

When you're ready to turn on automatic HTTPS, just replace your site's address (localhost in our tutorial) with your domain name. See our HTTPS quick-start guide for more information.

Multiple sites

With our current Caddyfile, we can only have the one site definition! Only the first line can be the address(es) of the site, and then all the rest of the file has to be directives for that site.

But it is easy to make it so we can add more sites!

Our Caddyfile so far:

localhost

encode zstd gzip
templates
file_server browse

is equivalent to this one:

localhost {
	encode zstd gzip
	templates
	file_server browse
}

except the second one allows us to add more sites.

By wrapping our site block in curly braces { } we are able to define multiple, different sites in the same Caddyfile.

For example:

:8080 {
	respond "I am 8080"
}

:8081 {
	respond "I am 8081"
}

When wrapping site blocks in curly braces, only addresses appear outside the curly braces and only directives appear inside them.

For multiple sites which share the same configuration, you can add more addresses, for example:

:8080, :8081 {
	...
}

You can then define as many different sites as you want, as long as each address is unique.

Matchers

We may want to apply some directives only to certain requests. For example, let's suppose we want to have both a file server and a reverse proxy, but we obviously can't do both on every request! Either the file server will write a response with a static file, or the reverse proxy will pass the request to a backend and write back its response.

This config will not work like we want (reverse_proxy will take precendence due to the directive order):

localhost

file_server
reverse_proxy 127.0.0.1:9005

In practice, we may want to use the reverse proxy only for API requests, i.e. requests with a base path of /api/. This is easy to do by adding a matcher token:

localhost

reverse_proxy /api/* 127.0.0.1:9005
file_server

There; now the reverse proxy will be prioritized for all requests starting with /api/.

The /api/* part we just added is called a matcher token. You can tell it's a matcher token because it starts with a forward slash / and it appears right after the directive (but you can always look it up in the directive's docs to be sure).

Matchers are really powerful. You can declare named matchers and use them like @name to match on more than just the request path! Take a moment to learn more about matchers before continuing!

Environment variables

The Caddyfile adapter allows substituting environment variables before the Caddyfile is parsed.

First, set an environment variable (in the same shell that runs Caddy):

export SITE_ADDRESS=localhost:9055

Then you can use it like this in the Caddyfile:

{$SITE_ADDRESS}

file_server

Before the Caddyfile is parsed, it will be expanded to:

localhost:9055

file_server

You can use environment variables anywhere in the Caddyfile, for any number of tokens.

Comments

One last thing that you will find most helpful: if you want to remark or note anything in your Caddyfile, you can use comments, starting with #:

# this starts a comment