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Jobs

Overview

A job, in contrast to a replication controller, runs a pod with any number of replicas to completion. A job tracks the overall progress of a task and updates its status with information about active, succeeded, and failed pods. Deleting a job will clean up any pod replicas it created. Jobs are part of the Kubernetes API, which can be managed with oc commands like other object types.

See the Kubernetes documentation for more information about jobs.

Creating a Job

A job configuration consists of the following key parts:

  • A pod template, which describes the application the pod will create.

  • An optional parallelism parameter, which specifies how many pod replicas running in parallel should execute a job. If not specified, this defaults to the value in the completions parameter.

  • An optional completions parameter, specifying how many concurrently running pods should execute a job. If not specified, this value defaults to one.

The following is an example of a job resource:

apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  parallelism: 1    (1)
  completions: 1    (2)
  template:         (3)
    metadata:
      name: pi
    spec:
      containers:
      - name: pi
        image: perl
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: Never

  1. Optional value for how many pod replicas a job should run in parallel; defaults to completions.

  2. Optional value for how many successful pod completions are needed to mark a job completed; defaults to one.

  3. Template for the pod the controller creates.

Scaling a Job

A job can be scaled up or down by using the oc scale command with the --replicas option, which, in the case of jobs, modifies the spec.parallelism parameter. This will result in modifying the number of pod replicas running in parallel, executing a job.

The following command uses the example job above, and sets the parallelism parameter to three:

$ oc scale job pi --replicas=3
Scaling replication controllers also uses the oc scale command with the --replicas option, but instead changes the replicas parameter of a replication controller configuration.

Setting Maximum Duration

When defining a Job, you can define its maximum duration by setting the activeDeadlineSeconds field. It is specified in seconds and is not set by default. When not set, there is no maximum duration enforced.

The maximum duration is counted from the time when a first pod gets scheduled in the system, and defines how long a job can be active. It tracks overall time of an execution and is irrelevant to the number of completions (number of pod replicas needed to execute a task). After reaching the specified timeout, the job is terminated by OpenShift Container Platform.

The following example shows the part of a Job specifying activeDeadlineSeconds field for 30 minutes:

  spec:
    activeDeadlineSeconds: 1800