OpenTelemetry metrics

The server exports metrics over OTLP/HTTP when OTEL_EXPORTER_OTLP_ENDPOINT is set. Export is disabled when the variable is empty. See Deployment for configuration and local inspection instructions.

Names below are the names sent through OTLP. An observability backend may normalize them; for example, a Prometheus-compatible backend can replace dots with underscores and add counter or unit suffixes.

Application metrics

Metric	Instrument	Unit	Description
backlog_holdem.http.server.requests	Counter	—	Completed observed HTTP requests.
backlog_holdem.http.server.request.duration	Histogram	s	Observed HTTP request duration.
backlog_holdem.http.server.active_requests	Up-down counter	—	Observed HTTP requests currently in progress.
backlog_holdem.room.commands	Counter	—	Completed room commands.
backlog_holdem.room.command.duration	Histogram	s	Room command duration.
backlog_holdem.realtime.connections	Up-down counter	—	Currently open SSE and WebSocket connections.
backlog_holdem.realtime.connection.duration	Histogram	s	Duration of closed SSE and WebSocket connections.
backlog_holdem.realtime.events.dropped	Counter	—	Room updates that could not be delivered to a subscriber because its channel remained full.
backlog_holdem.repository.operations	Counter	—	Completed room repository operations.
backlog_holdem.repository.operation.duration	Histogram	s	Room repository operation duration.
backlog_holdem.room.deleted	Counter	—	Rooms removed by the expiry cleanup worker.
backlog_holdem.deck.selected	Counter	—	Decks selected when rooms are created.
backlog_holdem.card.played	Counter	—	Cards played in successful votes.
backlog_holdem.room.active	Observable gauge	—	Non-ended rooms currently stored.
backlog_holdem.participant.active	Observable gauge	—	Current participants summed across non-ended rooms.

HTTP metrics cover /api/*, /events/*, and /ws/*. The /api/health endpoint and frontend routes and assets are excluded. Long-lived SSE and WebSocket requests remain active until their connection closes.

Metric attributes

Attribute	Metrics	Values
http.request.method	HTTP requests, duration, and active requests	HTTP method, such as GET or POST
http.route	Completed HTTP requests and duration	Route template, such as /api/rooms/{code}; never the room code
http.response.status_code	Completed HTTP requests and duration	Integer HTTP status code
backlog_holdem.command	Room commands and duration	create, join, vote, kick, reveal, end, reset, topic, or demo-team; WebSocket messages supply this value
backlog_holdem.transport	Room commands, command duration, connections, and connection duration	http, sse, or websocket, as applicable
backlog_holdem.outcome	Room commands, command duration, repository operations, and repository duration	success, rejected, or error for commands; success or error for repository operations
db.system.name	Repository operations and duration	sqlite or postgres
db.operation.name	Repository operations and duration	create, get, get_with_history, or save
reason	Deleted rooms	idle_timeout or session_ended
backlog_holdem.deck.type	Deck selections and cards played	fibonacci, modified-fibonacci, or tshirt-sizes
backlog_holdem.card.value	Cards played	A card from the selected deck

backlog_holdem.realtime.events.dropped has no metric attributes. The metrics do not contain room codes, participant identifiers, names, or topics. Card values are only exported from the fixed, low-cardinality decks listed above.

Go runtime metrics

The server also enables the OpenTelemetry Go runtime instrumentation:

Metric	Instrument	Unit	Description
go.memory.used	Observable up-down counter	By	Memory used by the Go runtime, split by go.memory.type (stack or other).
go.memory.limit	Observable up-down counter	By	Configured Go runtime memory limit. Omitted when no limit exists.
go.memory.allocated	Observable counter	By	Memory allocated to the heap by the application.
go.memory.allocations	Observable counter	{allocation}	Heap allocations made by the application.
go.memory.gc.goal	Observable up-down counter	By	Heap size target for the end of the garbage collection cycle.
go.goroutine.count	Observable up-down counter	{goroutine}	Live goroutines.
go.processor.limit	Observable up-down counter	{thread}	OS threads that can execute Go code simultaneously.
go.config.gogc	Observable up-down counter	%	Configured heap growth target percentage.

Resource attributes

Every metric is exported with resource attributes identifying the running server:

Attribute	Source
service.name	OTEL_SERVICE_NAME, default backlog-holdem
service.version	SERVICE_VERSION, otherwise the build revision or version
service.instance.id	Hostname, when available
deployment.environment.name	DEPLOYMENT_ENVIRONMENT, default development
vcs.ref.head.revision	Embedded build revision
gitlab.project.id	GITLAB_PROJECT_ID, when set
gitlab.project.name	GITLAB_PROJECT_NAME, when set

OTEL_RESOURCE_ATTRIBUTES can add or override resource attributes. Resource attributes may appear separately from data-point attributes in the observability backend.