A Pattern Sketch: Server-Sent Events as a Fanout Channel for Edge State

The project you've described, sse-edge-auth, is an interesting and innovative approach to managing state and caching in a distributed edge environment using Server-Sent Events (SSE) for coordination. Here's a summary of the key points along with some analysis:

Key Features

1. Server-Sent Events (SSE):

   • The master server uses SSE to push updates to connected edges.
   • Edges subscribe to these events and update their local SQLite databases accordingly.

2. Edge Caching:

   • Each edge maintains an in-memory cache of responses from the origin server, tagged with metadata for invalidation.
   • Cache entries are evicted based on a Least Recently Used (LRU) policy when the cache exceeds a predefined size.

3. Tag-Based Invalidation:

   • Origin server tags responses with specific identifiers (X-Cache-Tags header).
   • When content changes, the master sends an invalidation message to edges for specific tags.
   • Edges drop entries from their local SQLite caches that match the invalidated tags.

4. Local Rule Enforcement and Self-Healing:

   • Edges can enforce rules locally (e.g., auto-banning IPs after multiple authentication

Read the full article at DEV Community

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