Errors

Kestra provides multiple ways to handle errors, helping you both identify issues and decide whether your flows should stop or continue running after an error.

errors Component

errors is a list of tasks set at the flow level that are executed when an error occurs. You can add multiple tasks, and they are executed sequentially. This is useful for sending alerts when errors occur.

The example below sends a flow-level failure alert via Slack using the SlackIncomingWebhook task defined using the errors property.

id: errors
namespace: company.team


description: This will always fail


tasks:
  - id: failed_task
    type: io.kestra.plugin.core.execution.Fail


errors:
  - id: alert_on_failure
    type: io.kestra.plugin.notifications.slack.SlackIncomingWebhook
    url: secret('SLACK_WEBHOOK')
    messageText: "Failure alert for flow {{ flow.namespace }}.{{ flow.id }} with ID {{ execution.id }}"

Two kinds of error handlers can be defined:

  • Global: error handling global to a flow that must be at the root of the flow
  • Local: error handling local to a Flowable Task, handles errors for the flowable task and its children

Global Error Handler

This example shows a global error handler. The first task fails immediately, triggering the handler, which then logs the ID of the failed task using the errorLogs() function.

id: errors
namespace: company.team


tasks:
  - id: failed
    type: io.kestra.plugin.core.execution.Fail


errors:
  - id: 2nd
    type: io.kestra.plugin.core.log.Log
    message: I'm failing {{ errorLogs()[0]['taskId'] }} # Because errorLogs() is an array, the first taskId to fail is retrieved.
    level: INFO

Local Error Handler

This example demonstrates a local error handler that applies only to the children of t2. Errors from other tasks, like t1, are not handled here.

This can be useful to restrict error handling for a specific part of the flow and perform specific tasks like resource cleanup.

id: errors
namespace: company.team


tasks:
  - id: parent-seq
    type: io.kestra.plugin.core.flow.Sequential
    tasks:
      - id: t1
        type: io.kestra.plugin.core.debug.Return
        format: "{{task.id}} > {{taskrun.startDate}}"
      - id: t2
        type: io.kestra.plugin.core.flow.Sequential
        tasks:
          - id: t2-t1
            type: io.kestra.plugin.core.execution.Fail
        errors:
          - id: error-t1
            type: io.kestra.plugin.core.debug.Return
            format: "Error Trigger ! {{task.id}}"

allowFailure and allowWarning Property

When you execute a flow and one of its tasks fails, downstream tasks are not executed. This may not always be desirable, especially for non-critical tasks. You can resolve this by adding the allowFailure property to the task, which allows downstream tasks to continue despite an error. In this case, the execution will finish in a WARNING state.

id: allow_failure
namespace: company.team


description: This flow will allow a failure of a task (imagine a flaky unit test) and will continue processing downstream tasks, but the execution will finish in a `WARNING` state.


tasks:
  - id: first
    type: io.kestra.plugin.core.debug.Return
    format: "{{ task.id }} > {{ taskrun.startDate }}"


  - id: allow_failure
    type: io.kestra.plugin.core.execution.Fail
    allowFailure: true


  - id: last
    type: io.kestra.plugin.core.debug.Return
    format: "{{ task.id }} > {{ taskrun.startDate }}"

There’s also the allowWarning property which acts similar to the allowFailure property, but the execution will finish in a SUCCESS state even if warnings occurred.

id: allow_warning
namespace: company.team


description: This flow will allow a warning of a task (imagine a notification task) and will continue processing downstream tasks, with the execution finishing in a `SUCCESS` state even if warnings occurred.


tasks:
  - id: first
    type: io.kestra.plugin.core.debug.Return
    format: "{{ task.id }} > {{ taskrun.startDate }}"


  - id: allow_warning
    type: io.kestra.plugin.scripts.python.Script
    allowWarning: true
    beforeCommands:
      - pip install kestra
    script: |
      from kestra import Kestra


      logger = Kestra.logger()
      logger.warning("WARNING signals something unexpected.")

Best practices for error handling

  • Use global handlers for alerts and monitoring across the whole flow.
  • Use local handlers for targeted cleanup or retries.
  • Add allowFailure for non-critical tasks that shouldn’t block execution.
  • Use allowWarning when warnings should not mark the execution as failed.