4. Development

This page covers the relevant aspects for developers.

4.1. Repository

The Git repository for the exporter project is GitHub: https://github.com/zhmcclient/zhmc-prometheus-exporter

4.2. Code of Conduct

Contribution must follow the Code of Conduct as defined by the Contributor Covenant.

4.3. Contributing

Third party contributions to this project are welcome!

In order to contribute, create a Git pull request, considering this:

  • Test is required.

  • Each commit should only contain one “logical” change.

  • A “logical” change should be put into one commit, and not split over multiple commits.

  • Large new features should be split into stages.

  • The commit message should not only summarize what you have done, but explain why the change is useful.

  • The commit message must follow the format explained below.

What comprises a “logical” change is subject to sound judgement. Sometimes, it makes sense to produce a set of commits for a feature (even if not large). For example, a first commit may introduce a (presumably) compatible API change without exploitation of that feature. With only this commit applied, it should be demonstrable that everything is still working as before. The next commit may be the exploitation of the feature in other components.

For further discussion of good and bad practices regarding commits, see:

4.4. Making a change

To make a change, create a topic branch. You can assume that you are the only one using that branch, so force-pushes to that branch and rebasing that branch is fine.

When you are ready to push your change, describe the change for users of the package in a change fragment file. To create a change fragment file, execute:

For changes that have a corresponding issue:

towncrier create <issue>.<type>.rst --edit

For changes that have no corresponding issue:

towncrier create noissue.<number>.<type>.rst --edit

For changes where you do not want to create or modify a change log entry, simply don’t provide a change fragment file.

where:

  • <issue> - The issue number of the issue that is addressed by the change. If the change addresses more than one issue, copy the new change fragment file after its content has been edited, using the other issue number in the file name. It is important that the file content is exactly the same, so that towncrier can create a single change log entry from the two (or more) files.

    If the change has no related issue, use the noissue.<number>.<type>.rst file name format, where <number> is any number that results in a file name that does not yet exist in the changes directory.

  • <type> - The type of the change, using one of the following values:

    • incompatible - An incompatible change. This will show up in the “Incompatible Changes” section of the change log. The text should include a description of the incompatibility from a user perspective and if possible, how to mitigate the change or what replacement functionality can be used instead.

    • deprecation - An externally visible functionality is being deprecated in this release. This will show up in the “Deprecations” section of the change log. The deprecated functionality still works in this release, but may go away in a future release. If there is a replacement functionality, the text should mention it.

    • fix - A bug fix in the code, documentation or development environment. This will show up in the “Bug fixes” section of the change log.

    • feature - A feature or enhancement in the code, documentation or development environment. This will show up in the “Enhancements” section of the change log.

    • cleanup - A cleanup in the code, documentation or development environment, that does not fix a bug and is not an enhanced functionality. This will show up in the “Cleanup” section of the change log.

This command will create a new change fragment file in the changes directory and will bring up your editor (usually vim).

If your change does multiple things of different types listed above, create a separate change fragment file for each type.

If you need to modify an existing change log entry as part of your change, edit the existing corresponding change fragment file.

Add the new or changed change fragment file(s) to your commit. The test workflow running on your Pull Request will check whether your change adds or modifies change fragment files.

You can review how your changes will show up in the final change log for the upcoming release by running:

towncrier build --draft

Always make sure that your pushed branch has either just one commit, or if you do multiple things, one commit for each logical change. What is not OK is to keep the possibly multiple commits it took you to get to the final result for the change.

4.5. Format of commit messages

A commit message must start with a short summary line, followed by a blank line.

Optionally, the summary line may start with an identifier that helps identifying the type of change or the component that is affected, followed by a colon.

It can include a more detailed description after the summary line. This is where you explain why the change was done, and summarize what was done.

It must end with the DCO (Developer Certificate of Origin) sign-off line in the format shown in the example below, using your name and a valid email address of yours. The DCO sign-off line certifies that you followed the rules stated in DCO 1.1. In short, you certify that you wrote the patch or otherwise have the right to pass it on as an open-source patch.

We use GitCop during creation of a pull request to check whether the commit messages in the pull request comply to this format. If the commit messages do not comply, GitCop will add a comment to the pull request with a description of what was wrong.

Example commit message:

cookies: Add support for delivering cookies

Cookies are important for many people. This change adds a pluggable API for
delivering cookies to the user, and provides a default implementation.

Signed-off-by: Random J Developer <random@developer.org>

Use git commit --amend to edit the commit message, if you need to.

Use the --signoff (-s) option of git commit to append a sign-off line to the commit message with your name and email as known by Git.

If you like filling out the commit message in an editor instead of using the -m option of git commit, you can automate the presence of the sign-off line by using a commit template file:

  • Create a file outside of the repo (say, ~/.git-signoff.template) that contains, for example:

    <one-line subject>

<detailed description>

Signed-off-by: Random J Developer <random@developer.org>

  • Configure Git to use that file as a commit template for your repo:

    git config commit.template ~/.git-signoff.template

4.6. Releasing a version

This section shows the steps for releasing a version to PyPI.

It covers all variants of versions that can be released:

  • Releasing a new major version (Mnew.0.0) based on the master branch

  • Releasing a new minor version (M.Nnew.0) based on the master branch or based on an earlier stable branch

  • Releasing a new update version (M.N.Unew) based on the stable branch of its minor version

This description assumes that you are authorized to push to the remote repo at https://github.com/zhmcclient/zhmc-prometheus-exporter and that the remote repo has the remote name origin in your local clone.

Any commands in the following steps are executed in the main directory of your local clone of the zhmc-prometheus-exporter Git repo.

  1. On GitHub, verify open items in milestone M.N.U.

    Verify that milestone M.N.U has no open issues or PRs anymore. If there are open PRs or open issues, make a decision for each of those whether or not it should go into version M.N.U you are about to release.

    If there are open issues or PRs that should go into this version, abandon the release process.

    If none of the open issues or PRs should go into this version, change their milestones to a future version, and proceed with the release process. You may need to create the milestone for the future version.

  2. Run the Safety tool:

    make safety

    If any of the two safety runs fails, fix the safety issues that are reported, in a separate branch/PR.

    Roll back the PR into any maintained stable branches.

  3. Check for any dependabot alerts.

    If there are any dependabot alerts, fix them in a separate branch/PR.

    Roll back the PR into any maintained stable branches.

  4. Create and push the release branch (replace M,N,U accordingly):

    VERSION=M.N.U make release_branch

    This uses the default branch determined from VERSION: For M.N.0, the master branch is used, otherwise the stable_M.N branch is used. That covers for all cases except if you want to release a new minor version based on an earlier stable branch. In that case, you need to specify that branch:

    VERSION=M.N.0 BRANCH=stable_M.N make release_branch

    This includes the following steps:

    • create the release branch (release_M.N.U), if not yet existing

    • make sure the AUTHORS.md file is up to date

    • update the change log from the change fragment files, and delete those

    • commit the changes to the release branch

    • push the release branch

    If this command fails, the fix can be committed to the release branch and the command above can be retried.

  5. On GitHub, create a Pull Request for branch release_M.N.U.

    Important: When creating Pull Requests, GitHub by default targets the master branch. When releasing based on a stable branch, you need to change the target branch of the Pull Request to stable_M.N.

    Set the milestone of that PR to version M.N.U.

    This PR should normally be set to be reviewed by at least one of the maintainers.

    The PR creation will cause the “test” workflow to run. That workflow runs tests for all defined environments, since it discovers by the branch name that this is a PR for a release.

  6. On GitHub, once the checks for that Pull Request have succeeded, merge the Pull Request (no review is needed). This automatically deletes the branch on GitHub.

    If the PR did not succeed, fix the issues.

  7. On GitHub, close milestone M.N.U.

    Verify that the milestone has no open items anymore. If it does have open items, investigate why and fix (probably step 1 was not performed).

  8. Publish the package (replace M,N,U accordingly):

    VERSION=M.N.U make release_publish

    or (see step 4):

    VERSION=M.N.0 BRANCH=stable_M.N make release_publish

    This includes the following steps:

    • create and push the release tag

    • clean up the release branch

    Pushing the release tag will cause the “publish” workflow to run. That workflow builds the package, publishes it on PyPI, creates a release for it on GitHub, and finally creates a new stable branch on GitHub if the master branch was released.

  9. Verify the publishing

    Wait for the “publish” workflow for the new release to have completed: https://github.com/zhmcclient/zhmc-prometheus-exporter/actions/workflows/publish.yml

    Then, perform the following verifications:

4.7. Starting a new version

This section shows the steps for starting development of a new version.

This section covers all variants of new versions:

  • Starting a new major version (Mnew.0.0) based on the master branch

  • Starting a new minor version (M.Nnew.0) based on the master branch

  • Starting a new update version (M.N.Unew) based on the stable branch of its minor version

This description assumes that you are authorized to push to the remote repo at https://github.com/zhmcclient/zhmc-prometheus-exporter and that the remote repo has the remote name origin in your local clone.

Any commands in the following steps are executed in the main directory of your local clone of the zhmc-prometheus-exporter Git repo.

  1. Create and push the start branch (replace M,N,U accordingly):

    VERSION=M.N.U make start_branch

    This uses the default branch determined from VERSION: For M.N.0, the master branch is used, otherwise the stable_M.N branch is used. That covers for all cases except if you want to start a new minor version based on an earlier stable branch. In that case, you need to specify that branch:

    VERSION=M.N.0 BRANCH=stable_M.N make start_branch

    This includes the following steps:

    • create the start branch (start_M.N.U), if not yet existing

    • create a dummy change

    • commit and push the start branch (start_M.N.U)

  2. On GitHub, create a milestone for the new version M.N.U.

    You can create a milestone in GitHub via Issues -> Milestones -> New Milestone.

  3. On GitHub, create a Pull Request for branch start_M.N.U.

    Important: When creating Pull Requests, GitHub by default targets the master branch. When starting a version based on a stable branch, you need to change the target branch of the Pull Request to stable_M.N.

    No review is needed for this PR.

    Set the milestone of that PR to the new version M.N.U.

  4. On GitHub, go through all open issues and pull requests that still have milestones for previous releases set, and either set them to the new milestone, or to have no milestone.

    Note that when the release process has been performed as described, there should not be any such issues or pull requests anymore. So this step here is just an additional safeguard.

  5. On GitHub, once the checks for the Pull Request for branch start_M.N.U have succeeded, merge the Pull Request (no review is needed). This automatically deletes the branch on GitHub.

  6. Update and clean up the local repo (replace M,N,U accordingly):

    VERSION=M.N.U make start_tag

    or (see step 1):

    VERSION=M.N.0 BRANCH=stable_M.N make start_tag

    This includes the following steps:

    • checkout and pull the branch that was started (master or stable_M.N)

    • delete the start branch (start_M.N.U) locally and remotely

    • create and push the start tag (M.N.Ua0)

4.8. Building the distribution archives

You can build a binary (wheel) distribution archive and a source distribution archive (a more minimal version of the repository) with:

$ make build

You will find the files zhmc_prometheus_exporter-VERSION_NUMBER-py3-none-any.whl and zhmc_prometheus_exporter-VERSION_NUMBER.tar.gz in the dist folder, the former being the binary and the latter being the source distribution archive.

The binary distribution archive could be installed with:

$ pip install zhmc_prometheus_exporter-VERSION_NUMBER-py3-none-any.whl

The source distribution archive could be installed with:

$ tar -xfz zhmc_prometheus_exporter-VERSION_NUMBER.tar.gz
$ pip install zhmc_prometheus_exporter-VERSION_NUMBER

4.9. Building the documentation

You can build the HTML documentation with:

$ make builddoc

The root file for the built documentation will be build_docs/index.html.

4.10. Testing

You can perform unit tests with:

$ make test

The environment variables TESTCASES and TESTOPTS can be specified for unit tests. Invoke make help for details.

You can perform a flake8 check with:

$ make check

You can perform a pylint check with:

$ make pylint

4.11. Format of metric definition file

The metric definition file is in YAML format and has the following structure:

metric_groups:
  # dictionary of metric groups:
  {hmc-metric-group}:
    prefix: {resource-type}
    if: {fetch-condition}  # optional
    labels:
      # list of labels to be added to all metrics of this group:
      - name: {label-name}
        value: {label-value}

metrics:
  # dictionary of metric groups:
  {hmc-metric-group}:

    # dictionary format for defining metrics:
    {hmc-metric}:
      if: {export-condition}  # optional
      exporter_name: {exporter-name}
      exporter_desc: {exporter-desc}
      metric_type: {metric-type}
      percent: {percent-bool}
      valuemap: {valuemap}
      labels:
        # list of labels to be added to this metric:
        - name: {label-name}
          value: {label-value}

    # list format for defining metrics:
    - property_name: {hmc-metric}                     # either this
      properties_expression: {properties-expression}  # or this
      if: {export-condition}  # optional
      exporter_name: {exporter-name}
      exporter_desc: {exporter-desc}
      percent: {percent-bool}
      valuemap: {valuemap}
      labels:
        # list of labels to be added to this metric:
        - name: {label-name}
          value: {label-value}

fetch_properties:
  # dictionary of properties that need to be fetched because they can
  # change but have no property change notification
  {hmc-resource-class}:
    - property_name: {hmc-property}
      if: {fetch-condition}  # optional

Where:

  • {hmc-metric-group} is the name of the metric group on the HMC.

  • {hmc-metric} is the name of the metric (within the metric group) on the HMC.

  • {resource-type} is a short lower case term for the type of resource the metric applies to, for example cpc or partition. It is used in the Prometheus metric name directly after the initial zhmc_.

  • {fetch-condition} is a string that is evaluated as a Python expression and that indicates whether the metric group can be fetched. For the metric group to actually be fetched, the fetch property also needs to be True. The expression may use the following variables; builtins are not available:

    • hmc_version - HMC version as a tuple of integers (M, N, U), e.g. (2, 16, 0).

    • hmc_api_version - HMC API version as a tuple of integers (M, N), e.g. (4, 10).

    • hmc_features - List of names of HMC API features. Will be empty before HMC API version 4.10.

  • {properties-expression} is a Jinja2 expression whose value should be used as the metric value, for resource property based metrics. The expression uses the variable properties which is the resource properties dictionary of the resource. The properties_expression attribute is mutually exclusive with property_name.

  • {export-condition} is a string that is evaluated as a Python expression and that controls whether the metric is exported. If it evaluates to false, the export of the metric is disabled, regardless of other such controls. The expression may use the following variables; builtins are not available:

    • hmc_version - HMC version as a tuple of integers (M, N, U), e.g. (2, 16, 0).

    • hmc_api_version - HMC API version as a tuple of integers (M, N), e.g. (4, 10).

    • hmc_features - List of names of HMC API features. Will be empty before HMC API version 4.10.

    • se_version - SE/CPC version as a tuple of integers (M, N, U), e.g. (2, 16, 0). Will be None when there is no CPC context for the metric.

    • se_features - List of names of SE/CPC API features. Will be an empty list before HMC API version 4.10 or before SE version 2.16.0 or when there is no CPC context for the metric.

    • resource_obj - zhmcclient resource object for the metric.

  • {exporter-name} is the local metric name and unit in the exported metric name zhmc_{resource-type}_{exporter-name}. If it is null, the export of the metric is disabled, regardless of other such controls.

  • {exporter-desc} is the description text that is exported as # HELP.

  • {metric-type} is an optional enum value that defines the Prometheus metric type used for this metric: - “gauge” (default) - For values that can go up and down - “counter” - For values that are monotonically increasing counters

  • {percent-bool} is a boolean indicating whether the metric value should be divided by 100. The reason for this is that the HMC metrics represent percentages such that a value of 100 means 100% = 1, while Prometheus represents them such that a value of 1.0 means 100% = 1.

  • {valuemap} is an optional dictionary for mapping string enumeration values in the original HMC value to integers to be exported to Prometheus. This is used for example for the processor mode (shared, dedicated).

  • {label-name} is the label name.

  • {label-value} is a Jinja2 expression that is evaluated and used as the label value. For details, see Labels on exported metrics.

  • {hmc-resource-class} is the class of the HMC resource for which properties are to be fetched (i.e. the value of its class property, e.g. cpc).

  • {hmc-property} is the HMC name of the property that is to be fetched.