How Does HybridCache Manage Invalidation Across Pods in a Multi-Service Setup?

Hybrid caching in .NET 9 is designed to give you the fast, local access of an in‑memory cache while using a distributed cache (for example, Redis) as the centralized data source. However, the in‑memory portion is, by its nature, local to each pod.

How In‑Memory and Distributed Caching Work Together

• Distributed Cache as the Source of Truth:
  When you update or refresh data, the change is written to the distributed cache. All pods refer to this central store for the most recent value.

• Local In‑Memory Cache:
  Each pod caches data locally for performance reasons. This means that until an in‑memory entry expires or is explicitly refreshed, a pod may continue returning its locally cached data.

Invalidation Across Pods

There is no built‑in mechanism in the HybridCache library that automatically invalidates the in‑memory cache in other pods when data is updated in one pod. In other words:

• Without Customization:
  Each pod’s in‑memory cache is independent. A change in one pod (even though it updates the distributed cache) won’t automatically propagate to already cached items in other pods.

• Design Implication:
  This means that if immediate consistency across pods is a requirement, you need to adopt additional strategies such as:

  • Shorter Expiration Times:
    Configure the in‑memory cache entries with a short lifetime so they are refreshed at reasonable intervals.

  • Custom Invalidation Logic:
    Utilize a pub/sub mechanism (for example, with Redis) or another signaling approach so that when one pod updates the data, it can notify all pods to remove or refresh their local entries.

Summary

The HybridCache library leverages the distributed cache as the authoritative data source, but it does not include any built‑in mechanism for synchronizing in‑memory cache entries across pods. In a multi‑pod setup, if a pod’s in‑memory cache might become stale, you’ll need to implement additional invalidation or refresh logic based on your application needs.

This design is intentional because the in‑memory cache’s performance benefits come from the fact that it is local. For scenarios where cross‑pod consistency is critical, make sure to combine HybridCache with an appropriate invalidation strategy or a tighter expiration policy.