Add curl to images, for healthchecks

[nils-werner]

I've noticed that the caddy images don't contain the curl utility (at least the ones that I've built using -builder).

I'd suggest adding curl, because having something like it is really helpful to run health checks in the container. Of course you can convince wget to do the same, but I find it's more involved and a bit more annoying to set up. Especially because I haven't yet found a way to make wget not follow redirects, which in my case redirect from HTTP to the HTTPS endpoint, and then fail with a certificate error.

[francislavoie]

Since some users care about image size, I think it's best we only include packages that are generally useful for running Caddy itself and not stuff that's only useful for edgecases. You can simply add curl for yourself by writing a two line Dockerfile without it affecting all other users, so I suggest doing that instead.

[nils-werner]

I see what you mean, although I don't see using health checks in containers as an edge case, but rather good engineering practice no? I'd say it's ~300KB worth the investment.

[mholt]

Yeah I view curl as more of an API client and less of a downloader, like wget is tailored for.

300 KB isn't too drastic @francislavoie -- what do you think? Could make sense in a container that is all about web services.

[polarathene]

curl would normally bring in a bit of extra weight if it were a scratch image, but when you have Caddy added to an existing base with libc + openssl deps already it's not too bad.

If you deploy Caddy container with Docker Compose, adding packages is even more trivial tbh:

services:
  caddy:
    image: localhost/caddy-with-curl:latest
    pull_policy: build
    build:
      dockerfile_inline: |
        FROM caddy:2.10.2-alpine
        RUN apk add curl

---

I'd say it's ~300KB worth the investment.

Where are you getting the 300KB weight from though? I'm seeing 5 MiB added?

$ docker run --rm -it caddy:alpine ash
$ caddy --version
v2.10.2 h1:g/gTYjGMD0dec+UgMw8SnfmJ3I9+M2TdvoRL/Ovu6U8=

$ du -shx /
52.2M   /

$ apk add --no-cache curl
fetch https://dl-cdn.alpinelinux.org/alpine/v3.22/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.22/community/x86_64/APKINDEX.tar.gz
(1/9) Installing brotli-libs (1.1.0-r2)
(2/9) Installing c-ares (1.34.5-r0)
(3/9) Installing libunistring (1.3-r0)
(4/9) Installing libidn2 (2.3.7-r0)
(5/9) Installing nghttp2-libs (1.65.0-r0)
(6/9) Installing libpsl (0.21.5-r3)
(7/9) Installing zstd-libs (1.5.7-r0)
(8/9) Installing libcurl (8.14.1-r2)
(9/9) Installing curl (8.14.1-r2)
Executing busybox-1.37.0-r19.trigger
OK: 13 MiB in 32 packages

$ du -shx /
57.2M   /

---

For comparison... if you only need an HTTP client to perform a GET request for healthcheck functionality, you may like httpget (example usage) which can be compiled into a static binary and is as small as 128KB when I last tried it (or 70KB with UPX to compress it further).

An image build could pull the binary from the official repo's releases page (but that is a little over 500KB for HTTP-only vs my linked build advice), and that'd still be notably lighter than the curl dep shown above.