daemonset-job

README

daemonset-job

Kubernetes Operator for creating Jobs backed by Daemonsets.

Inspired by Run Once DaemonSet on Kubernetes by Everett Toews.

Following is an example of a cleanup job using a container that runs rm -rf. Filepath argument and mount path can be passed as part of the custom resource Job.

apiVersion: daemonset.darkowlzz.space/v1beta1
kind: Job
metadata:
  name: job-sample
spec:
  image: darkowlzz/cleanup:v0.0.2
  args: ["/basetarget/foo"]
  mountPath: "/tmp"

When deployed, this would execute rm -rf /tmp/foo on all the nodes.

Components

1. DaemonSet Job Controller

This controller watches the DaemonSet Job CRD resources. When a Job object is created, the controller creates and deploys a DaemonSet with container image JobSpec.Image. The controller then maintains or updates the DaemonSet, as per the JobSpec attributes.

2. Sidecar Job Terminator Container

This sidecar container monitors pods that are created by the Job DaemonSet and checks their status. When all the pods have completed their task, it terminates the associated Job.

Source: https://github.com/darkowlzz/daemonset-job-terminator

Special Container

DaemonSet Job depends on container logs to determine if a pod has completed its task. Hence, the containers need to be made in a specific way.

An example of a Dockerfile for a container:

FROM alpine:3.6
COPY script.sh .
RUN chmod u+x script.sh
ENTRYPOINT ["./script.sh"]

An example of the script above:

#!/bin/ash

set -euo pipefail

# Gracefully handle the TERM signal sent when deleting the daemonset
trap 'exit' TERM

# This is the main command that's run by this script on
# all the nodes.
rm -rf $1

# Let the monitoring script know we're done.
echo "done"

# this is a workaround to prevent the container from exiting
# and k8s restarting the daemonset pod
while true; do sleep 1; done

Once the task is completed, the container logs "done" and goes into a sleep mode. This is needed because DaemonSet requires pods to be running all the time.

When the sidecar container finds the termination word in the logs of a container, it counts the associated pod as completed. Once all the pods created by the daemonset have completed their task, the sidecar container deletes the parent Job custom resource. This results in cleanup of the daemonset and pods by garbage collection.

Deployment

Register the DaemonSet Job CRD:

$ kubectl apply -f config/crds/daemonset_v1beta1_job.yaml

Deploy the controller and sidecar:

$ kubectl apply -f deploy/

Try it

The Job manifest at the top would run rm -rf /tmp/foo on all the nodes. In a k8s cluster, after deploying the controller, create /tmp/foo file on all the nodes. Applying the Job manifest would delete the file and cleanup all the created resources.

Development

Run all the code checks and tests with make all.

Build a container image with IMG=<imagename> make docker-build.