feat(balancer): refresh uri and tls scheme in ai-proxy-advanced balancer phase

[oowl]

Summary

1. feat(patch): backport balancer.set_upstream_tls feature from openresty upstream feature: add balancer.set_upstream_tls(on). openresty/lua-resty-core#460
2. feat(patch): refresh upstream uri variable when proxy pass balancer recreate
3. feat(pdk): dynamic control upstream tls when kong.service.request.set_scheme was called
4. feat(llm): recreate http request header and body when balancer retry

Checklist

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

Issue reference

AG-183

[fffonion]

cc @ADD-SP this would need some performance test to validate

[ProBrian]

I'm not sure the performance impact here, is there a way to detect if the upstream tls option has been changed, and then decide if we need to do the config parsing again here? e.g. could we use ctx to mark if the options has been changed from lua side, and if not changed, we just skip the refresh of variables here?

[Oyami-Srk]

I don't think this patch is used to alter the TLS option. It looks like "reevaluating URI every time we make requests".
IIUC, before this patch, evaluating URI will perform only once when the config is processed and use evaluated value after that. Thus, altering some variables in URI will not be able to work normally.
I'm not sure if I understand correctly, Please correct me if I'm wrong. @oowl

[Oyami-Srk]

Just confirmed "feat(patch): refresh upstream uri variable when proxy pass balancer recreate" will cause regressions in RPS, latency and DP memory usage in change-route scenario.

[fffonion]

@Oyami-Srk The option to alter TLS on/off is from another commit in this PR. The change here is to alter upstream_uri,
as kong uses a variable in proxy_pass, this patch make sure in a failover when we update the upstream_uri, the variable is re-evaluated so that nginx will build an updated request on it.

[fffonion]

Just confirmed "feat(patch): refresh upstream uri variable when proxy pass balancer recreate" will cause regressions in RPS, latency and DP memory usage in change-route scenario.

@oowl I guess what we can do next to make sure this ngx_http_proxy_eval is only called the second time (aka in a failover) in a request.