Observability

ActionCache publishes a Meter and an ActivitySource, both named ActionCache. Neither does anything until something subscribes, so there is no flag to turn them on:

builder.Services.AddOpenTelemetry()
    .WithMetrics(metrics => metrics.AddMeter(ActionCacheDiagnostics.MeterName))
    .WithTracing(tracing => tracing.AddSource(ActionCacheDiagnostics.ActivitySourceName));

Metrics

Per request, or per operation

actioncache.requests and actioncache.evictions are recorded once per request, by the filters.

The other two are per backend operation, so a layered chain or a single-flight re-check contributes more than one measurement for a single request.

That distinction matters if you are deriving a hit ratio: use actioncache.requests, which counts requests. A counter recorded per backend read would give you a ratio of reads.

The namespace tag

Every namespace tag carries the unresolved template — Account:{id}, never Account:42. The resolved form is per-resource, which as a metric dimension is unbounded cardinality: one time series per account.

The outcome tag

actioncache.operation.duration records on every path, not just success. A backend that hangs until the operation timeout elapses is exactly what the histogram exists to expose, so failures and abandonments are sampled alongside successes. Without the outcome tag a timeout would be indistinguishable from a slow success.

Traces

Spans cover each backend operation and each refresh replay.

A degraded operation marks its own span as an error — not the ambient one. If nothing subscribes to ActionCache’s activity source, the current activity is the incoming request span, and marking that would report a request which returned 200 as failed simply because a cache read degraded exactly as fail-open intends.

RefreshReplay carries no namespace tag. It is a request path rather than a namespace, and a path is unbounded in the same way a resolved namespace is.

Logs

Beyond metrics and traces, the library logs:

• Degraded and fail-closed operations, at Warning, with the exception.
• Cache hits, misses, sets, evictions and refreshes, at Debug.
• Filter-level conditions the cache layer cannot see — a key that could not be built, a result that was not cacheable — at Debug.
• Refresh outcomes: a per-namespace summary, and each skipped or failed entry.
• Single-flight coalescing and lock timeouts.