Blog: Introducing Indexed Jobs
Signed-off-by: Aldo Culquicondor <acondor@google.com>
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title: "Introducing Indexed Jobs"
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date: 2021-04-19
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slug: introducing-indexed-jobs
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---
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**Author:** Aldo Culquicondor (Google)
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Once you have containerized a non-parallel [Job](/docs/concepts/workloads/controllers/job/),
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it is quite easy to get it up and running on Kubernetes without modifications to
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the binary. In most cases, when running parallel distributed Jobs, you had
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to set a separate system to partition the work among the workers. For
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example, you could set up a task queue to [assign one work item to each
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Pod](/docs/tasks/job/coarse-parallel-processing-work-queue/) or [multiple items
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to each Pod until the queue is emptied](/docs/tasks/job/fine-parallel-processing-work-queue/).
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The Kubernetes 1.21 release introduces a new field to control Job _completion mode_,
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a configuration option that allows you to control how Pod completions affect the
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overall progress of a Job, with two possible options (for now):
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- `NonIndexed` (default): the Job is considered complete when there has been
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a number of successfully completed Pods equal to the specified number in
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`.spec.completions`. In other words, each Pod completion is homologous to
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each other. Any Job you might have created before the introduction of
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completion modes is implicitly NonIndexed.
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- `Indexed`: the Job is considered complete when there is one successfully
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completed Pod associated with each index from 0 to `.spec.completions-1`. The
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index is exposed to each Pod in the `batch.kubernetes.io/job-completion-index`
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annotation and the `JOB_COMPLETION_INDEX` environment variable.
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You can start using Jobs with Indexed completion mode, or Indexed Jobs, for
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short, to easily start parallel Jobs. Then, each worker Pod can have a statically
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assigned partition of the data based on the index. This saves you from having to
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set up a queuing system or even having to modify your binary!
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## Creating an Indexed Job
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To create an Indexed Job, you just have to add `completionMode: Indexed` to the
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Job spec and make use of the `JOB_COMPLETION_INDEX` environment variable.
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```yaml
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apiVersion: batch/v1
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kind: Job
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metadata:
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name: 'sample-job'
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spec:
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completions: 3
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parallelism: 3
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completionMode: Indexed
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template:
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spec:
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restartPolicy: Never
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containers:
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- command:
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- 'bash'
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- '-c'
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- 'echo "My partition: ${JOB_COMPLETION_INDEX}"'
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image: 'docker.io/library/bash'
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name: 'sample-load'
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```
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Note that completion mode is an alpha feature in the 1.21 release. To be able to
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use it in your cluster, make sure to enable the `IndexedJob` [feature
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gate](/docs/reference/command-line-tools-reference/feature-gates/) on the
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[API server](docs/reference/command-line-tools-reference/kube-apiserver/) and
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the [controller manager](/docs/reference/command-line-tools-reference/kube-controller-manager/).
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When you run the example, you will see that each of the three created Pods gets a
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different completion index. For the user's convenience, the control plane sets the
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`JOB_COMPLETION_INDEX` environment variable, but you can choose to [set your
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own](/docs/tasks/inject-data-application/environment-variable-expose-pod-information/)
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or [expose the index as a file](/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/).
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See [Indexed Job for parallel processing with static work
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assignment](/docs/tasks/job/indexed-parallel-processing-static/) for a
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step-by-step guide, and a few more examples.
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## Future plans
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SIG Apps envisions that there might be more completion modes that enable more
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use cases for the Job API. We welcome you to open issues in
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[kubernetes/kubernetes](https://github.com/kubernetes/kubernetes) with your
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suggestions.
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In particular, we are considering an `IndexedAndUnique` mode where the indexes
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are not just available as annotation, but they are part of the Pod names,
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similar to {{< glossary_tooltip text="StatefulSet" term_id="statefulset" >}}.
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This should facilitate inter-Pod communication for tightly coupled Pods.
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You can join the discussion in the [open issue](https://github.com/kubernetes/kubernetes/issues/99497).
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## Wrap-up
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Indexed Jobs allows you to statically partition work among the workers of your
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parallel Jobs. SIG Apps hopes that this feature facilitates the migration of
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more batch workloads to Kubernetes.
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