Metric and label naming

The metric and label conventions presented in this document are not required for using Prometheus, but can serve as both a style-guide and a collection of best practices. Individual organizations may want to approach some of these practices, e.g. naming conventions, differently.

Metric names

A metric name...

  • ...must comply with the data model for valid characters.
  • ...should have a (single-word) application prefix relevant to the domain the metric belongs to. The prefix is sometimes referred to as namespace by client libraries. For metrics specific to an application, the prefix is usually the application name itself. Sometimes, however, metrics are more generic, like standardized metrics exported by client libraries. Examples:
    • prometheus_notifications_total (specific to the Prometheus server)
    • process_cpu_seconds_total (exported by many client libraries)
    • http_request_duration_seconds (for all HTTP requests)
  • ...must have a single unit (i.e. do not mix seconds with milliseconds, or seconds with bytes).
  • ...should use base units (e.g. seconds, bytes, meters - not milliseconds, megabytes, kilometers). See below for a list of base units.
  • ...should have a suffix describing the unit, in plural form. Note that an accumulating count has total as a suffix, in addition to the unit if applicable.
    • http_request_duration_seconds
    • node_memory_usage_bytes
    • http_requests_total (for a unit-less accumulating count)
    • process_cpu_seconds_total (for an accumulating count with unit)
    • foobar_build_info (for a pseudo-metric that provides metadata about the running binary)
    • data_pipeline_last_record_processed_timestamp_seconds (for a timestamp that tracks the time of the latest record processed in a data processing pipeline)
  • ...should represent the same logical thing-being-measured across all label dimensions.
    • request duration
    • bytes of data transfer
    • instantaneous resource usage as a percentage

As a rule of thumb, either the sum() or the avg() over all dimensions of a given metric should be meaningful (though not necessarily useful). If it is not meaningful, split the data up into multiple metrics. For example, having the capacity of various queues in one metric is good, while mixing the capacity of a queue with the current number of elements in the queue is not.

Labels

Use labels to differentiate the characteristics of the thing that is being measured:

  • api_http_requests_total - differentiate request types: operation="create|update|delete"
  • api_request_duration_seconds - differentiate request stages: stage="extract|transform|load"

Do not put the label names in the metric name, as this introduces redundancy and will cause confusion if the respective labels are aggregated away.

CAUTION: Remember that every unique combination of key-value label pairs represents a new time series, which can dramatically increase the amount of data stored. Do not use labels to store dimensions with high cardinality (many different label values), such as user IDs, email addresses, or other unbounded sets of values.

Base units

Prometheus does not have any units hard coded. For better compatibility, base units should be used. The following lists some metrics families with their base unit. The list is not exhaustive.

Family Base unit Remark
Time seconds
Temperature celsius celsius is preferred over kelvin for practical reasons. kelvin is acceptable as a base unit in special cases like color temperature or where temperature has to be absolute.
Length meters
Bytes bytes
Bits bytes To avoid confusion combining different metrics, always use bytes, even where bits appear more common.
Percent ratio Values are 0–1 (rather than 0–100). ratio is only used as a suffix for names like disk_usage_ratio. The usual metric name follows the pattern A_per_B.
Voltage volts
Electric current amperes
Energy joules
Power Prefer exporting a counter of joules, then rate(joules[5m]) gives you power in Watts.
Mass grams grams is preferred over kilograms to avoid issues with the kilo prefix.

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