DDD.Telemetry (vicander v0.1.1)

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The :telemetry events the framework emits, in one place.

Attach with :telemetry.attach_many/4, or feed them to Telemetry.Metrics / OpenTelemetry. Durations are in :native time units (System.convert_time_unit/3).

Spans (:start, :stop, :exception)

event prefixmetadata
[:ddd, :command]:command, and on stop :result (:ok/:error), :error_codes, :error_kind
[:ddd, :query]:query, and on stop :result, :error_codes, :error_kind
[:ddd, :handler, :deliver]:handler, :event, and on stop :outcome (:delivered, :skipped, :rejected, :error)
[:ddd, :projection, :rebuild]:projection, and on stop :events (how many were replayed)

Counters

eventmeasurementsmetadata
[:ddd, :command, :retry]%{attempt: n}:command
[:ddd, :repository, :conflict]%{count: 1}:aggregate, :id, :expected_version, :actual_version
[:ddd, :outbox, :poll]%{claimed: n}
[:ddd, :outbox, :published]%{count: 1, delay_ms: ms} (event age):event_type
[:ddd, :outbox, :retry]%{attempts: n, delay_ms: ms}:event_type, :error
[:ddd, :outbox, :dead_letter]%{attempts: n}:id, :event_type, :aggregate_type, :aggregate_id, :error

Gauges (call report/1, or let DDD.Health do it)

eventmeasurementsmetadata
[:ddd, :outbox, :stats]%{pending, in_flight, dead_letters, oldest_pending_age_ms}
[:ddd, :projection, :lag]%{pending, oldest_pending_age_ms}:projection

report/1 reads the database and emits the gauges, so run it on a timer (for example with :telemetry_poller) and chart them; an outbox that stops draining shows as a growing oldest_pending_age_ms.

Summary

Functions

events()

Every event name the framework emits (spans expand to start/stop/exception).

outbox_stats(repo)

The state of the outbox, straight from the table

report(repo, projections \\ [])

Emit the gauges ([:ddd, :outbox, :stats], and [:ddd, :projection, :lag] for each given projection) read from repo. Returns the outbox stats.

Functions

events()

@spec events() :: [[atom()]]

Every event name the framework emits (spans expand to start/stop/exception).

outbox_stats(repo)

@spec outbox_stats(module()) :: %{
  pending: non_neg_integer(),
  in_flight: non_neg_integer(),
  dead_letters: non_neg_integer(),
  oldest_pending_age_ms: non_neg_integer()
}

The state of the outbox, straight from the table:

  • :pending - waiting for delivery or a retry (not dead-lettered)
  • :in_flight - currently claimed by a poller
  • :dead_letters - given up on and not yet resolved
  • :oldest_pending_age_ms - how long the oldest pending event has been waiting (0 if none)

report(repo, projections \\ [])

@spec report(module(), [module()]) :: map()

Emit the gauges ([:ddd, :outbox, :stats], and [:ddd, :projection, :lag] for each given projection) read from repo. Returns the outbox stats.