Telemetry

Telemetry

Hooks (Carom)

CaromHooks has four process-wide delegates:

Hook	Payload	Raised when
OnRetry	RetrySignal: Attempt (1 for the first retry), Delay, ExceptionTypeName (null for a result retry)	A retry is about to wait
OnCircuitOpened	CircuitOpenedSignal: ServiceKey	A closed circuit opens, once per transition
OnBulkheadRejected	BulkheadRejectedSignal: ResourceKey	A full bulkhead turns a call away
OnRateLimitRejected	RateLimitRejectedSignal: ServiceKey	A throttle has no token

CaromHooks.OnRetry += s => logger.LogWarning("retry {Attempt} in {Delay}", s.Attempt, s.Delay);

Handlers run synchronously on the calling thread, so keep them fast. An exception thrown by a handler is caught and dropped so it cannot break the call it observes. With no handler set, nothing is computed or allocated.

OpenTelemetry (Carom.Telemetry.OpenTelemetry)

using Carom.Telemetry.OpenTelemetry;

CaromTelemetry.Subscribe();

builder.Services.AddOpenTelemetry()
    .WithMetrics(m => m.AddMeter(CaromTelemetry.MeterName));

Subscribe wires the hooks to these instruments on the Carom meter. It is safe to call more than once, and Unsubscribe removes exactly what it added.

Instrument	Type	Tags
carom.retry.count	counter	attempt, exception_type
carom.retry.delay	histogram, ms	none
carom.circuit_breaker.open.count	counter	service
carom.bulkhead.rejection.count	counter	resource
carom.rate_limit.rejection.count	counter	service

CaromTelemetry.StartActivity starts an activity on the Carom activity source for your own spans. Carom does not create spans on its own.