Explain proxyrunner session-aware backend pod routing

[yrobla]

Summary

run-mcp-k8s.mdx documented backendReplicas but gave no explanation of why Redis matters for backend scaling or how the proxy runner routes sessions to pods. Users could misconfigure or skip Redis when only scaling backends.

• Adds a Session routing for backend replicas subsection explaining that the proxy runner stores a session-to-pod mapping in Redis, what happens on backend pod restart, and why client-IP affinity is unreliable behind NAT
• Absorbs the previous standalone SessionStorageWarning note into the new subsection so the backendReplicas implication is explicit rather than buried
• Updates the Redis link to point directly to #horizontal-scaling-session-storage (added in Add horizontal scaling Redis session storage guide #709)

Test plan

• Section renders correctly in Docusaurus
• Redis link resolves to the correct anchor in the session storage guide

Closes #708

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Project	Deployment	Actions	Updated (UTC)
docs-website	Ready	Preview, Comment	Apr 14, 2026 1:35pm

[Copilot]

Pull request overview

Updates the Kubernetes “run MCP” guide to clarify why Redis is important when scaling backend replicas by documenting how the proxy runner performs session-aware routing to backend pods.

Changes:

• Added a “Session routing for backend replicas” subsection explaining Redis-backed session-to-pod routing, NAT pitfalls with client-IP affinity, and behavior on backend pod replacement.
• Merged the previous standalone SessionStorageWarning note into the new routing explanation so the backendReplicas implications are explicit.
• Updated the Redis session storage link to point at a specific in-page anchor.

[danbarr]

In the PR description you mentioned adding an anchor link to a new heading introduced in the unmerged #709. But the link is not actually present in this PR. Suggest making this one a draft dependent on 709, then add the anchor once it's present.

fixed

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

[Copilot]

The wording implies Redis is always used whenever backendReplicas > 1 ("the proxy runner uses Redis ..."), but the next paragraph describes behavior without Redis. Consider rephrasing to make it explicit that Redis-backed routing only applies when Redis session storage is configured, and otherwise the proxy runner relies on Service-level affinity (with the limitations described).

Suggested change

	same pod. When `backendReplicas > 1`, the proxy runner uses Redis to store a
	session-to-pod mapping so every proxy runner replica knows which backend pod
	owns each session.
	Without Redis, the proxy runner falls back to Kubernetes client-IP session
	affinity on the backend Service, which is unreliable behind NAT or shared egress
	IPs. If a backend pod is restarted or replaced, its entry in the Redis routing
	table is invalidated and the next request reconnects to an available pod —
	sessions are not automatically migrated between pods.
	same pod. When `backendReplicas > 1` and Redis session storage is configured,
	the proxy runner uses Redis to store a session-to-pod mapping so every proxy
	runner replica knows which backend pod owns each session.
	Without Redis session storage, the proxy runner relies on Kubernetes client-IP
	session affinity on the backend Service, which is unreliable behind NAT or
	shared egress IPs. If a backend pod is restarted or replaced, its entry in the
	Redis routing table is invalidated and the next request reconnects to an
	available pod — sessions are not automatically migrated between pods.

[Copilot]

The PR description says the Redis link was updated to point directly to #horizontal-scaling-session-storage, but this section still links to ./redis-session-storage.mdx without an anchor. Either update the link to match the description (once the heading exists) or adjust the PR description so it matches the actual change set.