Design for session persistence - Part II

[salonichf5]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format:

Problem: Users want sessionPersistence for their server communication

Solution: Add a detailed approach on how to support sessionPersistence for NGF while being community conformant.

Testing: Did a couple of manual checks

• IP hash working over a set of upstreams and what happens when it fails.
• GRPC connections sending cookie header and responding with correct backend when that cookie is used to send a request again.
• HTTPRoutes verified sessionPersistence working when right cookie sent back in the curl. If it fails, defaults to round robin while generating cookie ID each session.

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide
specific feedback, add them here.

Closes #4051

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

NONE

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.09%. Comparing base (b960d89) to head (a1694d5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4221      +/-   ##
==========================================
+ Coverage   86.08%   86.09%   +0.01%     
==========================================
  Files         131      131              
  Lines       14171    14174       +3     
  Branches       35       35              
==========================================
+ Hits        12199    12203       +4     
+ Misses       1768     1767       -1     
  Partials      204      204              

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[sjberman]

Be sure to fill out the security/testing/use case sections as provided in the proposal template.

[tataruty]

this design only discusses the cookie-based method and the rest are out of scope.
but we still have ip_hash design above, or it is just for general understanding?

[ciarams87]

🚀