# Cron trigger

## In this document
- [Overview](#overview)
- [Attributes](#attributes)
- [Examples](#examples)

## Overview

Triggers the function according to a schedule or interval, with an optional body.

## Attributes

| **Path**          | **Type**          | **Description**                                                                                                                                                                                    |
|:------------------|:------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| schedule          | string            | A cron-like schedule (for example, `*/5 * * * *`).                                                                                                                                                 |
| interval          | string            | An interval (for example, `1s`, `30m`).                                                                                                                                                            |
| concurrencyPolicy | string            | Concurrency policy - `"Allow"`, `"Forbid"`, or `"Replace"`; (default: `"Forbid"`). Applicable only when using CronJobs on Kubernetes platforms (see the [Kubernetes notes](#kubernetes-features)). |
| jobBackoffLimit   | int32             | The number of retries before failing a job; (default: `2`). Applicable only when using CronJobs on Kubernetes platforms (see the [Kubernetes notes](#kubernetes-features)).                        |
| event.body        | string            | The body passed in the event.                                                                                                                                                                      |
| event.headers     | map of string/int | The headers passed in the event.                                                                                                                                                                   |

### Notes about configuring attributes
> **Note:**
> 1. You must set either the [`schedule`](#attributes) or [`interval`](#attributes) mutually-exclusive attributes.
> 2. The `event.*` attributes are optional.

### Kubernetes features
**[Tech Preview]** On Kubernetes platforms, you can set the `cronTriggerCreationMode` platform-configuration field to `"kube"` to run the triggers as Kubernetes CronJobs instead of the default implementation of running Cron triggers from the Nuclio processor.
        For more information, see [Configuring a Platform](../../tasks/configuring-a-platform.md#cron-trigger-creation-mode-crontriggercreationmode).
        When running Cron triggers as CronJobs —
- The created CronJob uses `wget` to call the default HTTP trigger of the function according to the configured interval or schedule.
        (This means that worker-related attributes are irrelevant.)
    - The `wget` request is sent with the header `"x-nuclio-invoke-trigger: cron"`.
    - You can use the [`concurrencyPolicy`](#attributes) and [`jobBackoffLimit`](#attributes) attributes to configure the CronJobs.

<a id="examples"></a>
### Examples

```yaml
triggers:
  myCronTrigger:
    kind: cron
    attributes:
      interval: 3s
```

The following example is demonstrates a configuration for running Cron triggers as Kubernetes CronJobs, as it sets the `concurrencyPolicy` and `jobBackoffLimit` attributes.
Remember that this implementation requires setting the `cronTriggerCreationMode` platform-configuration field to `"kube"`.
See the [Kubernetes notes](#kubernetes-features).
```yaml
triggers:
  myCronTrigger:
    kind: cron
    attributes:
      interval: 10s
      concurrencyPolicy: "Allow"
      jobBackoffLimit: 2
```