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Debug

Overview

Debug spec is used for troubleshooting and breakpointing runtime resources. This doc helps understand the inner workings of debug in Tekton. Currently only the TaskRun resource is supported.

This is an alpha feature. The enable-api-fields feature flag must be set to "alpha" to specify debug in a taskRun.

Debugging TaskRuns

The following provides explanation on how Debugging TaskRuns is possible through Tekton. To understand how to use the debug spec for TaskRuns follow the TaskRun Debugging Documentation.

Breakpoint on Failure

Halting a TaskRun execution on Failure of a step.

Failure of a Step

The entrypoint binary is used to manage the lifecycle of a step. Steps are aligned beforehand by the TaskRun controller allowing each step to run in a particular order. This is done using -wait_file and the -post_file flags. The former let's the entrypoint binary know that it has to wait on creation of a particular file before starting execution of the step. And the latter provides information on the step number and signal the next step on completion of the step.

On success of a step, the -post-file is written as is, signalling the next step which would have the same argument given for -wait_file to resume the entrypoint process and move ahead with the step.

On failure of a step, the -post_file is written with appending .err to it denoting that the previous step has failed with and error. The subsequent steps are skipped in this case as well, marking the TaskRun as a failure.

Halting a Step on failure

The failed step writes <step-no>.err to /tekton/run and stops running completely. To be able to debug a step we would need it to continue running (not exit), not skip the next steps and signal health of the step. By disabling step skipping, stopping write of the <step-no>.err file and waiting on a signal by the user to disable the halt, we would be simulating a "breakpoint".

In this breakpoint, which is essentially a limbo state the TaskRun finds itself in, the user can interact with the step environment using a CLI or an IDE.

Exiting onfailure breakpoint

To exit a step which has been paused upon failure, the step would wait on a file similar to <step-no>.breakpointexit which would unpause and exit the step container. eg: Step 0 fails and is paused. Writing 0.breakpointexit in /tekton/run would unpause and exit the step container.

Breakpoint before step

TaskRun will be stuck waiting for user debugging before the step execution. When beforeStep-Breakpoint takes effect, the user can see the following information from the corresponding step container log:

debug before step breakpoint has taken effect, waiting for user's decision:
1) continue, use cmd: /tekton/debug/scripts/debug-beforestep-continue
2) fail-continue, use cmd: /tekton/debug/scripts/debug-beforestep-fail-continue
  1. Executing /tekton/debug/scripts/debug-beforestep-continue will continue to execute the step program
  2. Executing /tekton/debug/scripts/debug-beforestep-fail-continue will not continue to execute the task, and will mark the step as failed

Debug Environment

Additional environment augmentations made available to the TaskRun Pod to aid in troubleshooting and managing step lifecycle.

Mounts

/tekton/debug/scripts : Contains scripts which the user can run to mark the step as a success, failure or exit the breakpoint. Shared between all the containers.

/tekton/debug/info/<n> : Contains information about the step. Single EmptyDir shared between all step containers, but renamed to reflect step number. eg: Step 0 will have /tekton/debug/info/0, Step 1 will have /tekton/debug/info/1 etc.

Debug Scripts

/tekton/debug/scripts/debug-continue : Mark the step as completed with success by writing to /tekton/run. eg: User wants to exit onfailure breakpoint for failed step 0. Running this script would create /tekton/run/0 and /tekton/run/0/out.breakpointexit.

/tekton/debug/scripts/debug-fail-continue : Mark the step as completed with failure by writing to /tekton/run. eg: User wants to exit onfailure breakpoint for failed step 0. Running this script would create /tekton/run/0 and /tekton/run/0/out.breakpointexit.err.

/tekton/debug/scripts/debug-beforestep-continue : Mark the step continue to execute by writing to /tekton/run. eg: User wants to exit before step breakpoint for before step 0. Running this script would create /tekton/run/0 and /tekton/run/0/out.beforestepexit.

/tekton/debug/scripts/debug-beforestep-fail-continue : Mark the step not continue to execute by writing to /tekton/run. eg: User wants to exit before step breakpoint for before step 0. Running this script would create /tekton/run/0 and /tekton/run/0/out.beforestepexit.err.