Trigger is a mechanism that automates the execution of a flow.

Triggers can be scheduled or event-based.

Trigger types

Kestra supports both scheduled and external events.

Kestra core provides four types of triggers:

  • Schedule trigger allows you to execute your flow on a regular cadence e.g. using a CRON expression and custom scheduling conditions
  • Flow trigger allows you to execute your flow when another flow finishes its execution (based on a configurable list of states)
  • Webhook trigger allows you to execute your flow based on an HTTP request emitted by a webhook.
  • Realtime trigger allows you to execute your flow when events happen with millisecond latency.

Many other triggers are available from the plugins, such as triggers based on file detection events, e.g. the S3 trigger, or a new message arrival in a message queue, such as the SQS or Kafka trigger.

Trigger Common Properties

Following trigger properties can be set.

FieldDescription
idThe flow identifier, must be unique inside a flow.
typeThe Java FQDN of the trigger.
descriptionThe description of the trigger.
disabledSet it to true to disable execution of the trigger.
workerGroup.keyTo execute this trigger on a specific Worker Group (EE)

Trigger Variables

Triggers allow you to access trigger metadata through expressions e.g. {{ trigger.date }} to access the current date of the Schedule trigger, {{ trigger.uri }} to access the file or message from any file detection or message arrival event, as well as {{ trigger.rows }} for all Query triggers e.g. the PostgreSQL Query trigger.

This example will log the date when the trigger executes the flow:

yaml
id: variables
namespace: example

tasks:
  - id: hello
    type: io.kestra.plugin.core.log.Log
    message: "Hello World on {{ trigger.date }}! πŸš€"

triggers:
  - id: schedule
    type: io.kestra.plugin.core.trigger.Schedule
    cron: "@hourly"

Triggers restrict parallel execution for a given trigger ID to one active run. For instance, if an Execution from a flow with a Schedule trigger with ID hourly is still in a Running state, another one will not be started. However, you can still trigger the same flow manually (from the UI or API), and the scheduled Executions will not be affected.

yaml
id: hourlyFlow
namespace: example
tasks:
  - id: important-task
    type: io.kestra.plugin.core.log.Log
    message: If this runs for longer than 1h, next Executions will be queued rather than being started immediately
triggers:
  - id: hourly
    type: io.kestra.plugin.core.trigger.Schedule
    cron: "@hourly"

Conditions

Conditions are specific criteria or events that determine when a specific triggers should create a new execution. Usually, they limit the scope of a trigger to a specific set of cases.

For example, you can restrict a Flow trigger to a specific namespace prefix or execution status, and you can restrict a Schedule trigger to a specific time of the week or month.

You can pass a list of conditions; in this case, all the conditions must match to enable the current action.

Available conditions include:

You can also find datetime related conditions on the Schedule trigger page.

Unlocking, enabling and disabling triggers

Disabling a trigger in the source code

If you want to temporarily disable a trigger, you could do so by setting the disabled property to true, as you can see in the example below:

yaml
id: hello_world
namespace: example

tasks:
  - id: sleep
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.core.runner.Process
    commands:
      - sleep 30

triggers:
  - id: schedule
    type: io.kestra.plugin.core.trigger.Schedule
    cron: "*/1 * * * *"
    disabled: true

However, this approach requires changing the source code. A better approach is to use the Enabled toggle from the UI.

Disabling a trigger from the UI

You can disable or re-enable a trigger from the UI. Here is how you can do it:

  1. Go to the Flows page and click on the flow you want to disable the trigger for.
  2. Go to the Triggers tab and click on the Enabled toggle next to the trigger you want to disable. You can re-enable it by clicking the toggle again.

triggers_flow

If your trigger is locked due to an execution in progress, you can unlock it by clicking the Unlock trigger button.

trigger_unlock

The Unlock trigger functionality is useful for troubleshooting, e.g. if a process is stuck due to infrastructure issues. Note that manually unlocking triggers may result in multiple concurrent (potentially duplicated) executions β€” use it with caution.

Toggle or unlock triggers from the Administation page

You can also disable, re-enable, or unlock triggers from the Administration page. Here is how you can do it:

triggers_administration

The stopAfter property

Kestra 0.15 introduced a generic stopAfter property which is a list of states that will disable the trigger after the flow execution has reached one of the states in the list.

This property is meant to be used primarily for a Schedule trigger and triggers that poll for conditions including the HTTP, JDBC, or File Detection triggers. However, you can use it with all triggers.

Pause the schedule trigger after a failed execution

The stopAfter property can be used to pause a schedule trigger after a failed execution. Here is an example of how to use it:

yaml
id: business_critical_flow
namespace: production

tasks:
 - id: important_task
   type: io.kestra.plugin.core.log.Log
   message: if this fails, we want to stop the flow from running until we fix it

triggers:
 - id: stopAfter
   type: io.kestra.plugin.core.trigger.Schedule
   cron: "0 9 * * *"
   stopAfter:
     - FAILED

The above flow will be triggered every day at 9:00 AM, but if it fails, the schedule will be paused so that you can manually reenable the trigger once the issue is fixed. This is useful for business-critical flows that should not continue running the next scheduled executions if a previous execution has failed.

Disable the HTTP trigger after the first successful execution

The example below shows how to use the stopAfter property with the HTTP trigger condition. The use case is to poll an API endpoint and send a Slack alert if the price is below $110. If the condition is met, the trigger will be disabled so that you don't get alerted every 30 seconds about the same condition.

yaml
id: http
namespace: example

tasks:
  - id: slack
    type: io.kestra.plugin.notifications.slack.SlackIncomingWebhook
    url: "{{ secret('SLACK_WEBHOOK') }}"
    payload: |
      {
        "channel": "#price-alerts",
        "text": "The price is now: {{ json(trigger.body).price }}"
      }

triggers:
  - id: http
    type: io.kestra.plugin.fs.http.Trigger
    uri: https://fakestoreapi.com/products/1
    responseCondition: "{{ json(response.body).price <= 110 }}"
    interval: PT30S
    stopAfter:
      - SUCCESS

Let's break down the above example:

  1. The HTTP trigger will poll the API endpoint every 30 seconds to check if the price of a product is below $110.
  2. If the condition is met, the Execution will be created
  3. Within that execution, the slack task will send a Slack message to the #price-alerts channel to notify about the price change
  4. After that execution finishes successfully, the stopAfter property condition is met β€” it will disable the trigger ensuring that you don't get alerted every 30 seconds about the same condition.

Locked triggers

Flow, Schedule and Polling triggers have locks to avoid concurrent trigger evaluation and concurrent execution of a flow for a trigger.

To see a list of triggers and inspect their current status, go to the Administration -> Triggers section in the Kestra UI. From here, you can unlock a trigger if it is locked. Keep in mind that there is a risk or concurrent trigger evaluation or flow execution for this trigger if you unlock it manually.

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