Showing a maintenance message

[tcurdt (Torsten Curdt)]

1. The problem I’m having:

When I create a special file on disk I want to show a (maintenance) message instead of passing requests on to a reverse_proxy.

The provided config should work but I am wondering:

1. Could I deliver the content of the file “message.html” for (all requests) and still return a 503?

2. What is the performance impact of the file check? Will it check on disk for every request?

Or is there a better way of doing this?

2. Error messages and/or full log output:

NA

3. Caddy version:

$ caddy version
2.7.6

4. How I installed and ran Caddy:

NixOS via systemd

/nix/store/1cvy9h1k8lfc9na97g8fx6iy6sr5i3dz-caddy-2.7.6/bin/caddy run --config /etc/caddy/caddy_config --adapter caddyfile

a. System environment:

NixOS, arm

b. Command:

NA

c. Service/unit/compose file:

NA

d. My complete Caddy config:

{
    log {
        level ERROR
    }
}

echo1.vafer.com {
    log {
        output file /var/log/caddy/access-echo1.vafer.com.log
    }

    # if file "message.html" exist on disk show it

    root * /etc/caddy/message

    @exists {
      file message.html
    }

    handle @exists {
      respond "We will be back shortly" 503 {
        close
      }
    }

    # otherwise pass on to proxy

    handle {
      reverse_proxy echo1.default.svc.cluster.local:80
    }

    tls internal
}

5. Links to relevant resources:

[francislavoie]

@tcurdt

1. Could I deliver the content of the file “message.html” for (all requests) and still return a 503?

Yeah, you can override the status that file_server writes, see the docs. file_server (Caddyfile directive) — Caddy Documentation

@tcurdt

What is the performance impact of the file check? Will it check on disk for every request?

Yes, but syscalls for files are fast and generally cached, so it’s fine.

[tcurdt (Torsten Curdt)]

you can override the status that file_server writes, see the docs

Hm. But when the request is for /foo.html it would try to server foo.html, no?
And I would still want to serve message.html instead.

[francislavoie]

Then use a rewrite beforehand to change the path for the file to serve. Examples here: handle_errors (Caddyfile directive) — Caddy Documentation

In fact, you could just trigger an error when in maintenance, and then use handle_errors to serve the page.

@maintenance file /message.html
error @maintenance 503

handle_errors {
	@503 `{err.status_code} in [503]`
	handle @503 {
		rewrite * /message.html
		file_server
	}
}

The file_server directive is implemented such that if there’s an error in the stack, it’ll use the status code from that error when serving the file.

[tcurdt (Torsten Curdt)]

Thanks for the help again!