RequestRedirect filter on HTTPRoute cannot preserve path in request

[randmonkey]

Is there an existing issue for this?

• I have searched the existing issues

Does this enhancement require public documentation?

• I have added an Acceptance Criteria item for adding and/or adjusting public documentation (if applicable)

Problem Statement

From FTI-6305.
Because the RequestRedirect filter is implemented by request-termination and response-transformer plugin. This cannot include variable part in the response head. So the redirect path in the response body is fixed and cannot preserve path in the request.

Proposed Solution

• Use some other method to generate redirect response that can send variable response according to the request
  • For example: run a standalone server to send responses

Additional information

No response

Acceptance Criteria

• Redirect path in the response header can be preserved if no path is given
• ReplacePrefixMatch is also supported

[mheap]

Can this be implemented with a pre-function plugin?

kong.response.exit(301, 'redirecting', {['Location'] = 'https://other.example.com/' .. kong.request.get_path_with_query()})

[programmer04]

For redirect filter implementation in case of not using request-termination plugin please remember about extending

kubernetes-ingress-controller/internal/dataplane/translator/translate_upstreams.go

Lines 119 to 127 in 146ac05

	targets := lo.Values(targetMap)
	// Warn if an upstream was created with 0 targets and no request-termination plugin is present.
	// When the plugin is present there (may be a result of RequestRedirect filter) there may not be
	// a target service (it may point to an arbitrary URL), hence do not log a warn.
	if len(targets) == 0 && !lo.ContainsBy(service.Plugins, func(p kong.Plugin) bool {
	return p.Name != nil && *p.Name == "request-termination"
	}) {
	t.logger.V(logging.InfoLevel).Info("No targets found to create upstream", "service_name", *service.Name)
	}

[randmonkey]

@mheap has submitted a PR for adding a redirect plugin: Kong/kong#13900
Using the plugin (only for Kong 3.9, or other version that contains the plugin) should resolve this.
If Kong does not support this plugin, we should either:

• Do not support it and report a translation error
• Implement by pre-function plugin
  @mheap Which one do you think is the better resolution?

[mheap]

I think we should leave the existing implementation pre 3.9, and use the new plugin in 3.9+.

pre-function is used enough that I would not want to prevent users using it if adding redirects