argo-events-cronjob-trigger

argo-events-cronjob-trigger

An Argo Events Trigger to trigger a Kubernetes CronJob.

Background

It is quite easy to manually trigger a Kubernetes CronJob, e.g. via kubectl create job hello-job --from=cronjob/hello-cronjob. But doing this via Argo Events proved cumbersome, as the built-in K8s Resources trigger seems to lack support for --from.

Hence, we built this little trigger which creates a Job based on the spec.jobTemplate of any existing K8s CronJob.

Installation

Base

We recommend installing using Kustomize:

cd kustomize/base
kustomize edit set image cronjob-trigger=ghcr.io/j-be/argo-events-cronjob-trigger:<tag>
kubectl apply -k . -n <namespace>

where

• <tag> is the latest available version here
• <namespace> is the Kubernetes Namespace you want to deploy the trigger to. This may be the same namespace that Argo Events is deployed to, but it doesn't have to be.

The trigger provides a Service running on http://cronjob-trigger:9000. See here for details.

RBAC

The base installation creates a ServiceAccount as well as a ClusterRole which allows to get cronjobs and create jobs. See here for details.

But there is neither a ClusterRoleBinding nor RoleBinding included by default. In the spirit of "least privilege" we recommend creating RoleBindings in the namespaces the CronJobs to be triggerd reside. An example would be:

apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: cronjob-trigger-role-binding
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cronjob-trigger-role
subjects:
  - kind: ServiceAccount
    name: cronjob-trigger-sa
    namespace: <namespace>

where<namespace> is the Kubernetes Namespace the trigger was deployed to. See Base for details.

Usage

We assume you have Argo Events setup and working. If not, please consult the Argo Events Operator Manual.

We also assume you have an EventSource set up in Argo Events If not, please consult the Argo Events User Guide.

To trigger a CronJob named hello-cronjob located in the namespace hello-namespace create the following Sensor:

apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
  name: hello-cronjob-sensor
spec:
  dependencies:
    - name: hello
      eventSourceName: hello-eventsource
      eventName: hello-event
  triggers:
    - template:
        name: hello-trigger
        custom:
          serverURL: cronjob-trigger.<namespace>.svc:9000
          spec:
            namespace: hello-namespace
            cronjob: hello-cronjob

where <namespace> is the Kubernetes Namespace the trigger was deployed to. See Base for details.

For further details on Sensor please consult the Argo Events User Guide.