Identify and Re-run Flaky Tasks

Sometimes there are tasks in CI that can fail or succeed without any related code changes. These tasks are called flaky tasks. Because the cause of the flakiness can be difficult to determine, developers will typically re-run CI in the hopes that another run will cause the task to succeed and allow them to merge their PR. Every time a developer has to do this, it is harming their productivity and the productivity of the company as a whole.

Nx is perfectly positioned to detect which tasks are flaky and automatically re-run the flaky task in a different agent so that developers can have confidence that a failed CI pipeline is a real failure.

Identify Flaky Tasks

Nx creates a hash of all the inputs for a task whenever it is run. If Nx ever encounters a task that fails with a particular set of inputs and then succeeds with those same inputs, Nx knows for a fact that the task is flaky. Nx can't know with certainty when the task has been fixed to no longer be flaky, so if a particular task has no flakiness incidents for 2 weeks, the flaky flag is removed for that task.

Manually Mark a Task as Flaky or Not Flaky

If you need to manually mark a task as flaky or not flaky, you can do so from the run details screen. Flaky tasks will have a button that says Mark task as no longer flaky and failed tasks that are not flaky will have a button that says Mark task as likely flaky. Using these buttons, you can ensure that Nx Cloud treats tasks in the appropriate way.

Re-run Flaky Tasks

When a flaky task fails in CI with distributed task execution enabled, Nx will automatically send that task to a different agent and run it again (up to 2 tries in total). Its important to run the task on a different agent to ensure that the agent itself or the other tasks that were run on that agent are not the reason for the flakiness.