feat(conf): inject nginx directives into kong's proxy location block

[vvicaretti]

Summary

The injection of Nginx directives is currently supported in the http and server contexts, but not in the location context.

To inject Nginx directives into the location context, it is required to create and maintain a custom Nginx template, as detailed in this document.

The goal is to enable injection of Nginx location directives into the Kong Gateway’s proxy block, following the same pattern used for http and server contexts, without the need of a custom Nginx template.

This would streamline the process and maintain consistency across different Kong Gateway’s proxy contexts.

Checklist

• The Pull Request has tests
• A changelog file has been added to CHANGELOG/unreleased/kong or adding skip-changelog label on PR if unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Full changelog

• Add nginx_location_*. The new prefix allows for the dynamic injection of Nginx directives into the / location block within Kong's proxy server {} block.

Issue reference

Fix #[issue number]

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[bungle]

We also have indirection, e.g.:
https://github.com/Kong/kong/blob/master/kong/templates/nginx_kong.lua#L165
https://github.com/Kong/kong/blob/master/kong/templates/nginx_kong.lua#L196
https://github.com/Kong/kong/blob/master/kong/templates/nginx_kong.lua#L227
https://github.com/Kong/kong/blob/master/kong/templates/nginx_kong.lua#L258
https://github.com/Kong/kong/blob/master/kong/templates/nginx_kong.lua#L282

Thus I am not totally sure about this. @vvicaretti what are the reasons that you need to use custom template?

[vvicaretti]

@bungle since these are internal locations, I figured there is less need for end users to inject Nginx directives there.
Do you think it should be possible to modify them as well?

To expand a bit on the specific use case:

An application sets an X-Accel-Redirect header to instruct Nginx where to fetch static assets. This job is delegated to the Nginx-based Edge layer.
In an architecture where Kong sits in between the Edge layer and the application, it is required to instruct Kong to ignore and pass along the X-Accel-Redirect header.
The common pattern to do so would be to add the following directives under the relevant location block:

proxy_ignore_headers X-Accel-Redirect;
proxy_pass_header X-Accel-Redirect;

That's currently not possible, unless we use a custom template which makes upgrades tricky

[bungle]

since these are internal locations, I figured there is less need for end users to inject Nginx directives there

Those internal locations get used if you for example:

1. turn route.request_buffering=on
2. turn route.response_buffering=on
3. call kong.service.request.enable_buffering()
4. implement :response phase on an enabled plugin
5. proxy grpc traffic

So while they are internal, I feel we need to think wether we want the same directives replicated on each, or have their own injections.

[vvicaretti]

So while they are internal, I feel we need to think wether we want the same directives replicated on each, or have their own injections.

I believe it is up to the maintainers to decide what's the best way forward.
I would be happy to update the PR accordingly.

[jschmid1]

thanks for the nice contribution @vvicaretti. We had a look at this and this should be fine. I started the tests to see if anything breaks 👍🏼

[vvicaretti]

I have pushed this commit d1e177b to include a changelog file (the test was failing). I am afraid tests will have to be triggered one more time :)