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CONTRIBUTING.md

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How to Contribute

We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.

Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.

Code reviews

All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.

Community Guidelines

This project follows Google's Open Source Community Guidelines.

Contributing guidelines

Development environment

To prepare for development, you need to fork this repository and work on your own branch so that you can later submit your changes as a GitHub Pull Request.

Once you have forked the repo on GitHub, clone it locally and install the slo-generator in a Python virtual environment:

git clone github.com/google/slo-generator
cd slo-generator
python3 -m venv venv/
source venv/bin/activate

Install slo-generator locally in development mode, so that you can start making changes to it:

python setup.py develop

Adding support for a new backend or exporter

The slo-generator tool is designed to be modular as it moves forward. Users, customers and Google folks should be able to easily add the metrics backend or the exporter of their choosing.

New backend

To add a new backend, one must:

  • Add a new file slo-generator/backends/<backend>.py

  • Write a new Python class called <Backend> (CamlCase)

  • Add unit tests

Example with a fake Cat backend:

  • Add a new backend file:

    touch slo-generator/backends/cat.py

  • Fill the content of cat.py:

    from provider import CatClient

class CatBackend:
  def __init__(self, **kwargs):
    # instantiate your client here, or do nothing if your backend
    # doesn't need it.
    url = kwargs['url']
    self.client = CatClient(url)

  def _fmt_query(query, **options):
    # format your query string as you need to
    return query

  def query(self, *args, **kwargs):
    # add code to query your backend here.
    return self.client.query(*args, **kwargs)

  @staticmethod
  def count(timeseries):
    # add code to count the number of events in the timeseries returned
    return 500

  def distribution_cut(self, timestamp, window, slo_config):
    # this should return a tuple `(good_event_count, bad_event_count)`
    valid_event_query = slo_config['measurement']['query_valid']
    valid_timeseries = self.query(valid_event_query, timestamp, window)
    # ...
    return (good_count, bad_count)

  def good_bad_ratio(self, timestamp, window, slo_config):
    # this should return a tuple `(good_event_count, bad_event_count)`
    good_event_query = kwargs['measurement']['query_good']
    bad_event_query = kwargs['measurement']['query_bad']
    good_timeseries = self.query(good_event_query, timestamp, window)
    bad_timeseries = self.query(bad_event_query, timestamp, window)
    good_count = Datadog.count(good_timeseries)
    bad_count = Datadog.count(bad_timeseries)
    return (good_count, bad_count)

  def query_sli(self, timestamp, window, slo_config):
    # this should return a float `SLI value`.
    my_sli_value = self.compute_random_stuff()
    return my_sli_value

  • Write a sample SLO configs (slo_cat_test_slo_ratio.yaml):

    service_name: cat
feature_name: test
slo_name: slo
slo_description: Test Cat SLO
backend:
  class: Cat
  method: good_bad_ratio # change to test another method
  url: cat.mycompany.com
  measurement:
    query_good: avg:system.disk.free{*}.rollup(avg, {window})
    query_valid: avg:system.disk.used{*}.rollup(avg, {window})

  • Run a test with the SLO generator:

    slo-generator -f slo_cat_test_slo_ratio.yaml -b samples/error_budget_target.yaml

  • Create a directory samples/<backend> for your backend samples.

  • Add some YAML samples to show how to write SLO configs for your backend. Samples should be named slo_<service_name>_<feature_name>_<method>.yaml.

  • Add a unit test: in the tests/unit/test_compute.py, simply add a method called test_compute_<backend>. Take the other backends an example when writing the test.

  • Add documentation for your backend / exporter in a new file named docs/providers/cat.md.

The steps above are similar for adding a new exporter, but the exporter code will go to the exporters/ directory and the unit test will be named test_export_<exporter>.