Declarative Configuration in a lua file

[dorongold]

Summary

Currently Kong supports writing configuration in a file, in YAML or JSON.
To provide a more flexible configuration, especially for those running Kong in different environments (dev, staging, production), an option to write configuration in lua can be very useful.

Additional Details

There are many use-cases that come to mind:

• Using environment variables inside the declarative configuration, something like:

return {
services = {
  name = my-upstream
  url = os.getenv("UPSTREAM_URL_FOR_THIS_ENVRIONMENT")
   ...
  }
}

• Injecting parts of the configuration from a file, a Kubernetes config-map, or any other source which has different content in different environments.
  This can be done using lua functions such as dofile, load, loadfile, loadstring.

• etc.

[dorongold]

@hishamhm currently (after the issue you referenced is merged) this piece of code in kong/db/declarative/init.lua still blocks the use of Lua declarative configuration:

 -- do not accept Lua by default
  accept = accept or { yaml = true, json = true }

In addition, when you guys decide to fix that and support Lua declarative configuration, it would be nice to change this line setfenv(chunk, {}) and instead of setting an empty environment, at least pass in _G.os, so that os.getenv can be used inside the declarative configuration.

It would be nice the be updated here if and when this support is going to be added.

[mohatagarvit]

Should I make a different PR for these changes or continue in the last PR?

 -- do not accept Lua by default
  accept = accept or { yaml = true, json = true, lua = true }

setfenv(chunk, {_G.os}) in the elseif of lua

[andrepiske]

@dorongold I'm currently trying to put together a tool that allows to configure Kong in a declarative way, pretty much like you described here.

It's not open sourced yet, but I plan to do it in the foreseeable future.

I have a question though: Is your idea only for Kong configurations in the DB-less mode?

[dorongold]

@andrepiske We only use DB-less mode, so that is the only use-case I was aiming at.
Not sure what you mean about putting together a tool.
Declarative configuration using a Lua file is almost there.
All it takes is that someone from the Kong team merges the tiny 2 line change in the attached PR (or for them to create a similar PR themselves and merge it).

[andrepiske]

@dorongold Oh that might be it, you're using DB-less mode.
What I mean by the tool is that I'm creating a tool to declare configuration (services, routes, plugins etc) of Kong in a declarative way, similar to decK. But I think it wouldn't be appropriate for db-less mode :)