Nesting Matrices in Reusable Workflows can Bypass the 256 Jobs per Workflow Run Limit!

[nimadini]

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Hey team 👋

Actions doc notes a limit of 256 matrix jobs per workflow run, which I verified is indeed enforced.

However, with re-usable workflows, both the caller and the called workflow can define a matrix (even though I can't find it in the docs), which collectively can easily surpass the 256 limit, and GitHub allows it! For example, here is a successful workflow run with 129 * 2 = 258 matrix jobs (129 from the caller and 2 from the called workflow).

Nesting workflows up to 4 levels, one can in theory run 256 ^ 4 (i.e., 4,294,967,296) jobs per workflow run! 😮

I tried a benchmark with 3 levels of nested workflows (20 * 256 * 2 = 10,240). After about 600 successful matrix jobs, GitHub couldn't even load the workflow run page anymore and started to consistently time out (even though based on the actions tab the jobs are still running)!

As a result of this testing, Actions got disabled for my user account! 😢 (Created an issue for support to help re-enable it.)

Can you please confirm if (1) declaring nested matrices with re-usable workflows and (2) the total number of jobs in workflow surpassing 256 are features or bugs? 🤔

Thanks!

See the images below for more context:

A single workflow can't have more than 256 matrix jobs

Using nested matrices with re-usable workflows can surpass 256 jobs

After ~600 jobs GitHub can't load the workflow run anymore and is consistently timing out

Actions got disabled for my account due to this testing 😢

[gmondello]

hi @nimadini - Thanks for sharing this. Acknowledging this discussion and that I am working to gather answers to the questions you pose.

[goruha]

@nimadini, it seems that all you need to do is to avoid ban and page load-restricted concurrency preventing hitting GitHub API request limits.

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[markvai]

Hi, we are using GH nested matrix jobs and are very concerned about the actual limits, since those are not documented properly as seen above, can someone clarify?

[pfbyjy]

Hello, we are also using nested matrix jobs and it would be great to get an answer to this question