From 7aff4e1689bba9331e334135bf6542cd4f5656b6 Mon Sep 17 00:00:00 2001 From: Jay Faulkner Date: Wed, 17 Aug 2016 15:41:46 -0700 Subject: [PATCH] Add developer documentation on metrics Adds developer documentation to ironic-lib index page about how to emit metrics and what each metric type is useful for. Change-Id: I3e835717aa141f0e0fa0f026b910b9a9ed60665e Partial-bug: #1611559 --- doc/source/index.rst | 62 ++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 60 insertions(+), 2 deletions(-) diff --git a/doc/source/index.rst b/doc/source/index.rst index 230de135..973d1589 100644 --- a/doc/source/index.rst +++ b/doc/source/index.rst @@ -6,9 +6,67 @@ Overview ======== Ironic-lib is a library for use by projects under Bare Metal governance only. +This documentation is intended for developer use only. If you are looking for +documentation for deployers, please see the +`ironic documentation `_. + +Metrics +======= + +Ironic-lib provides a pluggable metrics library as of the 2.0.0 release. +Current provided backends are the default, 'noop', which discards all data, +and 'statsd', which emits metrics to a statsd daemon over the network. The +metrics backend to be used is configured via ``CONF.metrics.backend``. How +this configuration is set in practice may vary by project. + +The typical usage of metrics is to initialize and cache a metrics logger, +using the `get_metrics_logger()` method in `ironic_lib.metrics_utils`, then +use that object to decorate functions or create context managers to gather +metrics. The general convention is to provide the name of the module as the +first argument to set it as the prefix, then set the actual metric name to the +method name. For example:: + + from ironic_lib import metrics_utils + + METRICS = metrics_utils.get_metrics_logger(__name__) + + @METRICS.timer('my_simple_method') + def my_simple_method(arg, matey): + pass + + def my_complex_method(arg, matey): + with METRICS.timer('complex_method_pt_1'): + do_some_work() + + with METRICS.timer('complex_method_pt_2'): + do_more_work() + +There are three different kinds of metrics: + - **Timers** measure how long the code in the decorated method or context + manager takes to execute, and emits the value as a timer metric. These + are useful for measuring performance of a given block of code. + - **Counters** increment a counter each time a decorated method or context + manager is executed. These are useful for counting the number of times a + method is called, or the number of times an event occurs. + - **Gauges** return the value of a decorated method as a metric. This is + useful when you want to monitor the value returned by a method over time. + +Additionally, metrics can be sent directly, rather than using a context +manager or decorator, when appropriate. When used in this way, ironic-lib will +simply emit the value provided as the requested metric type. For example:: + + from ironic_lib import metrics_utils + + METRICS = metrics_utils.get_metrics_logger(__name__) + + def my_node_failure_method(node): + if node.failed: + METRICS.send_counter(node.uuid, 1) + +The provided statsd backend natively supports all three metric types. For more +information about how statsd changes behavior based on the metric type, see +`statsd metric types `_ -Index -===== Generated Developer Documentation =================================