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Humpback

Overview

A simple pod scheduler which waits for the pod's result.
This tool can help external Job scheduler to trigger pod execution.

Cases wherein you need to execute commands inside an image, this tool can come in handy to make sure you are able to execute a completable command inside your image without the need to stand up an SSH daemon for Job orchestrator to connect to.

This will also allow a more granular resource allocation per job. This results to better kubernetes cluster resource utilization.

Configuration

There is a minimum configuration this tool requires.

  1. humpback.yaml

This configuration should contain all the "applications" that the pod runner can schedule.

Sample configuration:

applications:
- name: app1
  template: /app1-templates/pod1.tmpl
  container:
    resource-requests:
      memory: 10Mi
      cpu: 
    resource-limits:
      memory: 50Mi
      cpu:
    image: balchua/app1:1.0
    uid: 1000
    gid: 1000
- name: app2
  template: /app2-templates/pod1.tmpl
  container:
    resource-requests:
      memory: 10Mi
      cpu: 200m
    resource-limits:
      memory: 50Mi
      cpu: 100m
    image: balchua/demo:1.0
    uid: 2000
    gid: 2000
  1. Pod templating

There is a need to provide a pod template, which will allow the runner to dynamically interpolate pod commands, memory and cpu (requests / limits) and image to use.

Sample template:

apiVersion: v1
kind: Pod
metadata:
  name: {{ .Name }}-{{ .UniqueId }}
  labels:
    app: {{ .Name }}
    appUnique: {{ .Name }}-{{ .UniqueId }}
spec:
  containers:
  - image: {{ .Container.Image }}
    args: [{{ .Container.Arguments }}]
    imagePullPolicy: IfNotPresent
    name: {{ .Name }}
    securityContext:
      runAsUser: {{ .Container.UID }}
      fsGroup: {{ .Container.GID }}

Some few notes to remember the pod runner will automatically set the restartPolicy to Never otherwise the Pod will go into CrashLoop If possible, set the activeDeadlineSeconds to make sure that the Pod does not run indefinitely.

Executing the humpback

humpback --application [your application name] --namespace [the namespace where you want the job to run] --command [the Job's command] --kube-config $KUBECONFIG --appconfig-path /tmp

Where:

  • --application or -a should be the name of the application defined in the humpback.yaml

  • --namespace or -n which namespace the pod will be scheduled.

  • --command or -c The actual command to run.

  • --kubeconfig or -k If you are running this outside the Kubernetes cluster, specify this, otherwise leave it empty.

  • --appconfig-path or -p Additional path to search for humpback application config. example /tmp/

Any Pod Status, that results to other than Successful will be returned as an error i.e. exit(1)

Abrupt shutdown

The pod runner will react to SIGTERM, SIGQUIT, SIGKILL and SIGHUP. Thes os signals will force humpback to delete the pod. Signalling to terminate the "Job". This is to avoid excessive "completed" or "failed" pods in the cluster, relieving potential cluster space pressure.

Cleanup

The controller will automatically delete the pod, as soon as it completes or failed. The pod logs are tailed to the console.

Limitations

The command to run will not be able to interpolate any environment variables defined at the Container args.

For example:

/usr/src/app/main-good.sh $APP_HOME - the $APP_HOME will not be interpolated. In order to mitigate this, the $APP_HOME must be resolved from inside the shell script, in this case /usr/src/app/main-good.sh

If the Pod goes into ImagePullError, the pod runner does not appear to detect this, leaving it in Pending mode. It will not complete. This is now supported. While the PodStatus is in Pending state, and if the containerStatus is not ContainerCreating its assumed to be an ImagePullError.

Build

  • Clone the repo.

  • Enable GO module export GO111MODULE=on

  • Run go build

Examples

Check out the directory examples