Add support for kamal-proxy's path-prefix

[ACPK]

This PR introduces support for kamal-proxy's new path-based routing feature. For applications that split their traffic to different services based on the request path, you can use path-based routing to mount services under different path prefixes.

Begin by deploying the primary app that doesn’t require a path_prefix. Once that’s live, deploy your secondary app with the same host and the path_prefix feature.

Example Usage

# config/deploy.yml
...
servers:
  web:
    - 192.168.0.1

proxy:
  # Don't include ssl (TLS) options
  hosts:
    - callred.com
  path_prefix: '/api'
  # strip_path_prefix: true
...

NOTE: SSL options (e.g., ssl: true) should be set in the proxy for the app without a path_prefix, so the app above uses SSL by inheritance. Repeating the SSL settings here will cause the deploy to fail with a TLS error in the console.

With the above configuration, all incoming requests to https://callred.com/api/* will be routed to your service. By default, the path prefix will be stripped from the request before it is forwarded upstream. So in the example above, a request to /api/users/123 will be forwarded to the secondary app as /users/123. To instead forward the request with the original path (including the prefix), set: strip_path_prefix: true

Testing until added to main branch

For testing, I used the following setup in my Gemfile:

gem 'kamal', require: false, git: 'https://github.com/acpk/kamal.git', branch: 'kamal-proxy-path-prefix'

Deployment was performed with:

bundle exec kamal deploy

[brgmn]

Just some small newline fixes. The rest looks fine! Thanks for your integration work! Looking forward to being able to use path_prefix natively in kamal!

[brgmn]

Something seems to be wrong with newlines here

[ACPK]

What do you mean?

[brgmn]

@ACPK Sorry. My fault. I just didn't understand the markdown logic. After looking at it again everything seems to be fine.

[shiny]

I was wondering if there's any update on merging the PR?