fix(runloop): use upstream status code in passive health check

[oowl]

Summary

We expect the upstream passive unhealthy healthcheck on HTTP status code should only mark the targets as "down" (not reachable or proxiable) using the returned HTTP status code from the target, and it should not be affected by the final HTTP status code set by Kong plugin, which is returned to the client.

So we change the passive health check implementation to use nginx var upstream_code, this will not be changed by any plugin.

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Full changelog

• [Implement ...]

Issue reference

FTI-4841
Fix #10281

[hbagdi]

The reason for the fix makes sense. Please add a test.

[hbagdi]

Please add a changelog entry.

[team-gateway-bot]

The backport to release/3.0.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.0.x release/3.0.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.0.x
# Create a new branch
git switch --create backport-10325-to-release/3.0.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbe8d947e7d6a6c12f8464fc2f08276be1cd392f
# Push it to GitHub
git push --set-upstream origin backport-10325-to-release/3.0.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.0.x

Then, create a pull request where the base branch is release/3.0.x and the compare/head branch is backport-10325-to-release/3.0.x.

[team-gateway-bot]

The backport to release/3.1.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.1.x release/3.1.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.1.x
# Create a new branch
git switch --create backport-10325-to-release/3.1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbe8d947e7d6a6c12f8464fc2f08276be1cd392f
# Push it to GitHub
git push --set-upstream origin backport-10325-to-release/3.1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.1.x

Then, create a pull request where the base branch is release/3.1.x and the compare/head branch is backport-10325-to-release/3.1.x.

[team-gateway-bot]

The backport to release/3.2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.2.x release/3.2.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.2.x
# Create a new branch
git switch --create backport-10325-to-release/3.2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbe8d947e7d6a6c12f8464fc2f08276be1cd392f
# Push it to GitHub
git push --set-upstream origin backport-10325-to-release/3.2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.2.x

Then, create a pull request where the base branch is release/3.2.x and the compare/head branch is backport-10325-to-release/3.2.x.