Add transform encoder to Caddy build by default

[hookenz]

👉 Describe the problem

By default, the configured output of Caddy logs is console output which is only slightly more readable than JSON logs.
Especially when wrapping in a tailed terminal window during development. It's not really a format designed for easy consumption by humans.

👥 Problem evidence & reach

(#283 (comment))

🏆 How to solve this problem

There is a caddy module written by the caddy authors called "transform-encoder". But it's not included by default. However, I personally would love it to be built into your images by default. It will sit there dormant until configured by some environment var(s).

I'm not sure why the caddy authors didn't add it by default. The caddy webpage states their strong opinion for structured JSON logs which might be why. My personal opinion is if it's only ever going to be for human consumption then why make it difficult. It would be nice to allow a personal preference.

Detail 1

We would just need to add this to the caddy build step.

xcaddy ... --with github.com/caddyserver/transform-encoder 

For further info see:

• https://caddyserver.com/docs/caddyfile/directives/log#format-modules
• https://caddyserver.com/docs/modules/caddy.logging.encoders.transform

Detail 2

Possible Env var option:

$CADDY_LOG_FORMAT="transform '{common_log}'"

Caddyfile

... format {$CADDY_OUTPUT_FORMAT:console} 

I do think maybe format {$CADDY_LOG_FORMAT:console} should be defined in the Caddyfile in the current beta 4 so users can add "json" as the output format.

i.e.

$CADDY_LOG_FORMAT="json" 

🥰 Describe the "impact" on users?

So by default output looks the same as it does now. But I have the option of using common_log format if I wish.
Or defining my own template according to the transform encoder docs.

💯 How do we validate the problem is solved?

Users will have the ability ability to enable common_log format or other flexible formats with environment vars(s) without having to create a custom build.