custom.md

Custom

slo-generator allows you to load custom backends / exporters dynamically.

This enables you to:

• Support other backends or exporters that are not part of slo-generator core.
• Query or export from / to internal custom APIs.
• Create SLOs based on more complicated logic (e.g: fetch a Datastore record or run a BQ query).

Backend

To create a custom backend, simply create a new file and add the backend code within it.

For this example, we will assume the backend code below was added to custom/custom_backend.py.

A sample custom backend will have the following look:

class CustomBackend:
    def __init__(self, client=None, **kwargs):
        # create a client for your backend using **kwargs, use existing one, or
        # just ignore the init.
        # **kwargs are the fields specified in the backend section of your
        # SLO Config YAML file.
        pass

    def good_bad_ratio(self, timestamp, window, slo_config):
        # compute your good bad ratio in this method.
        # you can do anything here (query your internal API, correlate with 
        # other data, etc...)
        # return a tuple (number_good_events, number_bad_events)
        return (100000, 100)

    def query_sli(self, timestamp, window, slo_config):
        # compute your SLI value directly.
        # return a float or integer.
        return 0.999

In order to call the good_bad_ratio method in the custom backend above, the backend block would look like this:

backend:
  class:  custom.custom_backend.CustomBackend # relative Python path to the backend. Make sure  __init__.py is created in subdirectories for this to work.
  method: good_bad_ratio                      # name of the method to run
  arg_1:  test_arg_1                          # passed to kwargs in __init__
  arg_2:  test_arg_2                          # passed to kwargs in __init__

→ Full SLO config

Exporter

To create a custom exporter, simply create a new file and add the exporter code within it.

For the examples below, we will assume the exporter code below was added to custom/custom_exporter.py.

Standard

A standard exporter:

• must implement the export method.

A sample exporter looks like:

class CustomExporter:
    """Custom exporter."""

    def export(self, data, **config):
        """Export data.

        Args:
            data (dict): Data to send.
            config (dict): Exporter config.

        Returns:
            object: Custom exporter response.
        """
        # export your `data` (SLO report) using `config` to setup export 
        # parameters that need to be configurable.
        return {
            'status': 'ok',
            'code': 200,
            'arg_1': config['arg_1']
        }

and the corresponding exporters section in your SLO config:

exporters:
- class: custom.custom_exporter.CustomExporter
  arg_1: test

Metrics

A metrics exporter:

• must inherit from slo_generator.exporters.base.MetricsExporter.
• must implement the export_metric method which exports one metric as a dict like:

  {
      "name": <METRIC_NAME>,
      "alias": <METRIC_NAME_RELABELED>,
      "additional_labels": [
          <METRIC_LABEL_1>,
          <METRIC_LABEL_2>
      ],
      "value": <METRIC_VALUE>,
      "timestamp": <METRIC_TIMESTAMP>,
      "description": <METRIC_DESCRIPTION>
  }

A sample metrics exporter will look like:

from slo_generator.exporters.base import MetricsExporter

class CustomExporter(MetricsExporter): # derive from base class
    """Custom exporter."""

    def export_metric(self, data):
        """Export data to Stackdriver Monitoring.

        Args:
            data (dict): Metric data.

        Returns:
            object: Stackdriver Monitoring API result.
        """
        # implement how to export 1 metric here...
        return {
            'status': 'ok',
            'code': 200,
        }

and the exporters section in your SLO config:

exporters:
  - class: custom.custom_exporter.CustomExporter
    arg_1: test

Note:

The MetricsExporter base class has the following behavior:

• The metrics block in the SLO config is passed to the base class MetricsExporter
• The base class MetricsExporter runs the export method which iterates through each metric and add information to it, such as the current value and timestamp.
• The base class MetricsExporter calls the derived class export_metric for each metric and pass it the metric data to export.
• The derived class for each metric to export. See metrics for more details on the metrics block.