coherent format of container labels describing proxy behavior

[royra]

Current labels:

• preevy.access
• preevy.inject_script
• preevy.expose

Goals:

• support multiple ports per container
• support multiple behavior properties per port: private/public, injection
• support multiple routes (aliases) per container port, each with its own behavior
• sane defaults
• consistent naming and scheme for labels
• given a set of labels, the proxy agent can print the normalized configuration labels which is complete (like e.g, docker compose config)

Example 1 - defaults

services:
  my-service:
    ports:
    - 3000
    - 8080:8080
    - 8081:8081

can be normalized into:

services:
  my-service:
    ports:
    - 3000
    - 8080:8080
    - 8081:8081

    labels:
      preevy.routes.[3000].port: 3000
      preevy.routes.[3000].access: public
      preevy.routes.[8080].port: 8080
      preevy.routes.[8080].access: public
      preevy.routes.[8081].port: 8081
      preevy.routes.[8081].access: public

and results the following routes:

• my-service-3000: port 3000, public
• my-service-8080: port 8080, public
• my-service-8081: port 8081, public

Example 2

services:
  my-service:
    ports:
    - 3000
    - 8080:8080
    - 8081:8081
    
    labels:
      # global default
      preevy.access: private 

      preevy.routes.[8080].access: public

      preevy.routes.web.port: 3000

      preevy.routes.web-with-tool.port: 3000
      preevy.routes.web-with-tool.inject_script.x.src: http://my-script.com

can be normalized into:

services:
  my-service:
    ports:
    - 3000
    - 8080:8080
    - 8081:8081
    
    labels:
      preevy.routes.web.port: 3000
      preevy.routes.web.access: private
      preevy.routes.web-with-tool.port: 3000
      preevy.routes.web-with-tool.access: private
      preevy.routes.web-with-tool.inject_script.x.src: http://my-script.com
      preevy.routes.[8080].port: 8080
      preevy.routes.[8080].access: public
      preevy.routes.[8081].port: 8081
      preevy.routes.[8081].access: private

and results the following routes:

• web: port 3000, public
• web-with-tool: port 3000, private, injects script http://my-script.com
• my-service-8080: port 8080, public
• my-service-8081: port 8081, private

note that the default route for port 3000 my-service-3000 is not created because its port is specified in the web and web-with-tool routes.

Edge cases

Missing port

    labels:
      preevy.routes.web.access: private    

This configuration is invalid: there is no preevy.routes.web.port label, can't determine the port for route web.

Redirecting default routes

    labels:
      preevy.routes.[8080].port: 3000

This configuration is valid albeit confusing. It creates the route my-service-8080 with port 3000 and disables the default route for port 3000 my-service-3000.

[aleclerc-cio]

I really like this format. It seems flexible enough and can be augmented with new features. I believe it would satisfy all my use cases in #421