Why Does Restarting a Reverse Proxy Invalidate Every Session for One Self-Hosted App?

A reverse-proxy restart logs out every user only when it also changes, loses, or reroutes the session state used by that application.

A basic proxy usually forwards cookies rather than owning the application session, so a proxy restart alone should not invalidate every login. The real trigger may be a restarted authentication gateway, a regenerated cookie-signing secret, an in-memory session cache, a backend replica change, or a Compose dependency that restarts the app with the proxy. Identify which component issued and validates the session before changing cookie attributes or forcing users to sign in again.

Confirm Which Services Restarted With the Proxy

Record container IDs, start times, restart counts, health events, and logs for the reverse proxy, authentication service, application, cache, and database before and after one controlled proxy restart.

Docker Compose can restart dependent services when a dependency is explicitly configured for restart propagation. The official startup-order guidance shows why a command described as a proxy restart may also replace or restart an authentication or application container.

If only the proxy receives a new start time, focus on proxy-managed authentication, routing, and cookies. If the app, cache, or auth gateway also restarts, inspect their session persistence and secrets first.

Identify Which Layer Issued the Login Cookie

Before restarting, record the cookie name, domain, path, Secure, HttpOnly, SameSite, expiration, and whether the application or an authentication gateway sets it.

MDN explains that cookie scope and attributes determine where a browser sends it, but those attributes do not reveal which backend validates its value.

Compare response headers from the login request and the first request after restart. A missing cookie is a browser-scope problem; an unchanged cookie rejected by the server points to lost state, changed keys, or a different backend.

Check Whether an Authentication Gateway Regenerated Its Session Secret

Inspect the auth gateway’s secret source, file mount, environment, container recreation, and generated configuration. Compare the value source before and after restart without exposing the secret itself.

Authelia documents that its session secret encrypts stored session data, so changing or losing that secret prevents the service from reading sessions created earlier.

Store session secrets in a persistent secret file or managed secret store rather than generating them during each container start. Rotate deliberately with a documented logout window.

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Rule Out an In-Memory Session Store

Identify whether the application stores sessions in process memory, a local cache, Redis, a database, or signed client cookies. Compare session-store process uptime with the logout event.

Django warns that a cache-only session backend can lose session data when the cache is restarted or evicted, which logs users out when session data disappears.

If the proxy stack includes the cache container, restarting that stack may erase sessions even though the application container remains up. Use a persistent cache configuration or a database-backed fallback when login continuity matters.

Compare Application Signing Keys Across Restarts

Inspect the application’s session-signing or encryption key source and determine whether the key is persisted, loaded from the expected env file, or generated at startup.

Flask uses SECRET_KEY to sign session cookies, so replacing that key makes existing signed cookies invalid even when the browser continues sending them.

Do not solve this by sharing one secret among unrelated applications. Give each app a stable secret, protect it as backup-critical configuration, and verify it survives image recreation.

Check Sticky Sessions and Backend Replica Changes

List backend replicas, their session stores, and the proxy’s load-balancing policy. Test whether the same user stays logged in when requests reach another replica.

Traefik’s sticky-session configuration routes a client back to one backend, but users can still lose sessions if replicas do not share state and a restart changes the selected endpoint.

Stickiness can hide an incorrectly local session store. Prefer shared durable session state when multiple app replicas are intended to survive proxy or backend replacement.

Reproduce With One Test Account and Stable Configuration

Snapshot configuration, log in with one disposable account, record the session identifiers, restart only the proxy, and test the same request before restarting any other component.

The ZimaSpace article on outside-only login loops covers path-dependent login failures; this article focuses on simultaneous invalidation of already valid sessions after restart.

The issue is resolved when proxy-only restarts preserve sessions, deliberate auth or app restarts use stable secrets and persistent state, and every replica accepts the same active login.

Frequently Asked Questions

Can a reverse proxy itself store user sessions?

It can when it includes an authentication gateway, access middleware, or sticky-session mechanism. A simple forwarding proxy usually does not own the application login session.

Does restarting Redis always log out users?

Only when sessions exist solely in Redis and its data is not persisted or restored. Applications using database-backed or signed-cookie sessions behave differently.

Should I increase cookie lifetime to stop restart logouts?

No. A longer-lived cookie still fails if its signing key changes or its server-side session record disappears. Fix persistence and secret stability first.