Caddy in Docker with common_log

As of Caddy v2.5.0 they have "removed the deprecated common_log field from HTTP access logs, and the single_field encoder.". For me as a casual user of Caddy who mostly just looks at logs this is inconvenient. I don't use any tools to analyse json files for automation, maybe I should? However, the good folks at Caddy doesn't leave us high and dry. "If you relied on this, you may use the transform encoder plugin to encode logs in Common Log format.". But, since I am using Docker the version of Caddy I pull down from Docker Hub does not have this plugin available... Enter the builder.

According to Caddy's official Docker Hub documentation, we need to create our own Dockerfile with the builder image (caddy:builder) and then create our own Caddy image.

This is how the Dockerfile looks like:

ARG VERSION=2.5.2

FROM caddy:${VERSION}-builder AS builder

RUN xcaddy build \
  --with github.com/caddyserver/transform-encoder

FROM caddy:${VERSION}

COPY --from=builder /usr/bin/caddy /usr/bin/caddy

The magic part is the line:

RUN xcaddy build \
  --with github.com/caddyserver/transform-encoder
Which pulls the transform-encoder plugin and installs it. Then we are switching to a "normal" Caddy image and just replacing the binary with our custom built one.

Now you just need to build and run this Dockerfile locally!

Caddyfile

This is the syntax to use it in a Caddyfile:

log {
        format transform "{common_log}"
        output file /var/log/homepage.log
    }

tl;dr

docker pull mroggy85/caddy:2.5.2

See my Docker Hub Page: https://hub.docker.com/r/mroggy85/caddy

Original blog post: https://okuno.se/blog/caddy-in-docker-with-common-log