Session Management in Distributed Systems
As your application scales across multiple services and regions, managing user sessions becomes exponentially more complex. A single user might have sessions across mobile apps, web browsers, and API clients, all requiring instant invalidation when security events occur. This is where a well-designed distributed session management system becomes your safeguard against unauthorized access and data breaches.
Architecture Overview
A robust distributed session management system sits at the intersection of security and scalability, requiring careful orchestration between multiple components. At its core, you'll have a Session Store (typically Redis or a similar fast data store) that maintains active sessions with their metadata and expiration times. This sits behind a Session Manager service that handles creation, validation, and lifecycle operations. Additionally, you need an Authentication Service that generates session tokens, an Event Bus for broadcasting invalidation events across services, and a User Service that manages user accounts and password changes.
The architecture follows a publish-subscribe pattern where critical events like password changes trigger cascading invalidation across the entire session ecosystem. When a user initiates a password change, the User Service doesn't just update credentials, it broadcasts an event that the Session Manager consumes immediately. Each microservice that validates sessions listens to these events, ensuring no orphaned sessions persist in distributed caches. This event-driven approach eliminates the race condition problem you'd encounter with synchronous calls, where some services might still accept an invalidated session while others reject it.
Token design plays a crucial role in this architecture. Rather than storing all session data server-side, many distributed systems use signed JWT tokens with short expiration windows paired with refresh tokens that have longer lifespans. This reduces Session Store load and allows offline validation in some scenarios. However, the invalidation challenge becomes more critical, since a token remains cryptographically valid until its expiration time passes. The Session Manager maintains a revocation list for these tokens, checking it during validation to catch any sessions that should have been terminated early.
The Password Change Scenario
When a user changes their password, invalidating all active sessions requires atomic coordination across your distributed system. Here's how it flows: the User Service receives the password change request and, after updating credentials, publishes a "UserPasswordChanged" event with the user ID. The Session Manager subscribes to this event and immediately queries the Session Store for all active sessions belonging to that user. It then removes each session record and publishes a "SessionsRevoked" event containing the user ID and session IDs. Every service that caches session validation results receives this event and purges their local caches, preventing stale session acceptance. For JWT-based systems, the revoked session IDs get added to a temporary revocation list (stored with a TTL matching the JWT expiration time) that validators check during authentication. This multi-layer invalidation ensures that even if a user's token was just validated microseconds before the password change, the next request will fail because that session now appears in the revocation list.
Watch the Full Design Process
Watch how these concepts come together in real-time as we build this architecture from scratch. See how each component fits into the larger system and understand the tradeoffs between consistency, performance, and operational complexity.
Try It Yourself
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