layer-metrics

Reactive charm layer supporting Juju metrics collection.

Usage

Add this layer to your charm's layer.yaml:

includes:
 - layer:metrics

Collecting metrics

Declare metrics in your charm's metrics.yaml. For example:

metrics:
  users:
    type: gauge
    description: number of users
    command: scripts/count_users.py --global
  transactions:
    type: absolute
    description: number of new transactions since last measurement
    command: scripts/stats.py | awk '{print $3}'

Supported metric types

type: gauge metrics are values that measure some quantity at the time of capture.

type: absolute metrics report the amount added since last time.

The juju-units metric

The built-in Juju metric juju-units sends a "1" value for each Juju unit. This is useful for deriving units- or applications- per time-period. To enable it, simply declare:

metrics:
  juju-units:

without any attributes.

Collection commands

command: specifies a shell command to execute, which takes a reading of the metric. The command must write a single, postive numeric string to stdout. This string may be an integer (like 15) or a decimal (like 3.1415).

The current working directory for the command is the charm directory.

Caveat

Metrics may be collected concurrently with Juju hook execution, so the Juju hook context is not available. Most hook tools, such as config-get, config-set, and wrappers such as charmhelpers.core.hookenv cannot be used from within the collection commands.

charmhelpers.core.unitdata is available, and is the preferred means of coordination between reactive handler functions or charm hooks, and the metric collection context.