Update github-actions-secrets.md
Cautions on using GitHub Actions with extensive processes like build tests.
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**GitHub <a href="https://help.github.com/en/actions/getting-started-with-github-actions/about-github-actions" target="_blank">Actions</a>** help you automate your software development workflows in the same place you store code and collaborate on pull requests and issues. You can write individual tasks, called actions, and combine them to create a custom workflow. Workflows are custom automated processes that you can set up in your repository to build, test, package, release, or deploy any code project on GitHub.
+***A note on testing***: Some projects would like to use GitHub Actions for complex processes, such as automating their tests of software builds.
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+The _time_ runners are in use (measured in minutes) is unlimited for public repositories so how long a test takes isn't the issue. The issue is tying up limited 'runners' (nodes) while those minutes are running. Apache has 180 runners for over 1200 repositories, so the concern would be how many runners the test requires, which are then unavailable to other projects for the duration of the test. Out of those 180 runners, only 50 Mac OS runners that can be in use at one time for all ASF projects.
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+The ASF maxes out its runner allocation quite often, so a project needs to plan carefully to make best use of them for everyone's sake. For example, it would be important not to trigger a full release test with a pull request that is correcting a typo on one page in one module.
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+If you are considering using GitHub Actions in this way, please subscribe to the `builds@ a.o` mailing list, where there is a continuing discussion on this topic and others related to continuious integration development.
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See <a href="https://cwiki.apache.org/confluence/display/INFRA/Github+Actions+to+DockerHub" target="_blank">Apache Airflow's experience</a> with Actions.
**GitHub <a href="https://help.github.com/en/actions/configuring-and-managing-workflows/creating-and-storing-encrypted-secrets" target="_blank">Secrets</a>** are encrypted environment variables that you create in a repository or organization. The secrets you create are available to use in GitHub Actions workflows.
