Telemetry

Introduction

TODO: metrics crate, metric types.

All metrics are provided with the actor_group and, optionally, actor_key labels. The last one is added for actor groups with enabled system.telemetry.per_actor_key option.

Read more information about metric types.

TODO: tips, prefer increment_gauge! over gauge!

Configuration

Telemetry can be configured separately for each actor group. Possible options and their default values:

[some_group]
system.telemetry.per_actor_group = true
system.telemetry.per_actor_key = false

Note that using per_actor_key can highly increase a number of metrics. Use it only for low cardinality groups.

TODO: elfo-telemeter config.

Built-in metrics

elfo is shipped with a lot of metrics. All of them start with the elfo_ prefix to avoid collisions with user defined metrics.

Statuses

  • Gauge elfo_active_actors{status}

    The number of active actors in the specified status.

  • Gauge elfo_restarting_actors

    The number of actors that will be restarted after some time.

  • Counter elfo_actor_status_changes_total{status}

    The number of transitions into the specified status.

Messages

  • Counter elfo_sent_messages_total{message, protocol}

    The number of sent messages.

  • Summary elfo_message_handling_time_seconds{message, protocol}

    Spent time on handling the message, measured between (try_)recv() calls. Used to detect slow handlers.

  • Summary elfo_message_waiting_time_seconds

    Elapsed time between send() and corresponding recv() calls. Usually it represents a time that a message spends in a mailbox. Used to detect places that should be sharded to reduce a total latency.

  • Summary elfo_busy_time_seconds

    Spent time on polling a task with an actor. More precisely, the time for which the task executor is blocked. Equals to CPU time if blocking IO isn't used.

Log events

  • Counter elfo_emitted_events_total{level}

    The number of emitted events per level (Error, Warn, Info, Debug, Trace).

  • Counter elfo_limited_events_total{level}

    The number of events that haven't been emitted because the limit was reached.

  • Counter elfo_lost_events_total{level}

    The number of events that hasn't been emitted because the event storage is full.

Dump events

  • Counter elfo_emitted_dumps_total

    The number of emitted dumps.

  • Counter elfo_limited_dumps_total

    The number of dumps that haven't been emitted because the limit was reached.

  • Counter elfo_lost_dumps_total

    The number of dumps that hasn't been emitted because the dump storage is full.

Other metrics

TODO: specific to elfo-logger, elfo-dumper, elfo_telemeter

Derived metrics

TODO

Dashboards

TODO

Implementation details

TODO