Volcano Job Plugin -- Env User Guide

Last updated on Feb 4, 2026

Background

Env Plugin is designed for business that a pod should be aware of its index in the task such as MPI and TensorFlow. The indices will be registered as environment variables automatically when the Volcano job is created. For example, a tensorflow job consists of 1 ps and 2 workers. And each worker maps to a slice of raw data. In order to make the workers be aware of its target slice, they get their index in the environment variables.

Key Points

The index keys of the environment variables are VK_TASK_INDEX and VC_TASK_INDEX, they have the same value.
The value of the indices is a number which ranges from 0 to length - 1. The length equals to the number of replicas of the task. It is also the index of the pod in the task.

Examples

apiVersion: batch.volcano.sh/v1alpha1
kind: Job
metadata:
  name: tensorflow-dist-mnist
spec:
  minAvailable: 3
  schedulerName: volcano
  plugins:
    env: []   ## Env plugin register, note that no values are needed in the array.
    svc: []
  policies:
    - event: PodEvicted
      action: RestartJob
  queue: default
  tasks:
    - replicas: 1
      name: ps
      template:
        spec:
          containers:
            - command:
                - sh
                - -c
                - |
                  PS_HOST=`cat /etc/volcano/ps.host | sed 's/$/&:2222/g' | sed 's/^/"/;s/$/"/' | tr "\n" ","`;
                  WORKER_HOST=`cat /etc/volcano/worker.host | sed 's/$/&:2222/g' | sed 's/^/"/;s/$/"/' | tr "\n" ","`;
                  export TF_CONFIG={\"cluster\":{\"ps\":[${PS_HOST}],\"worker\":[${WORKER_HOST}]},\"task\":{\"type\":\"ps\",\"index\":${VK_TASK_INDEX}},\"environment\":\"cloud\"};   ## Get the index from the environment variable and configure it in the TF job.
                  python /var/tf_dist_mnist/dist_mnist.py
              image: volcanosh/dist-mnist-tf-example:0.0.1
              name: tensorflow
              ports:
                - containerPort: 2222
                  name: tfjob-port
              resources: {}
          restartPolicy: Never
    - replicas: 2
      name: worker
      policies:
        - event: TaskCompleted
          action: CompleteJob
      template:
        spec:
          containers:
            - command:
                - sh
                - -c
                - |
                  PS_HOST=`cat /etc/volcano/ps.host | sed 's/$/&:2222/g' | sed 's/^/"/;s/$/"/' | tr "\n" ","`;
                  WORKER_HOST=`cat /etc/volcano/worker.host | sed 's/$/&:2222/g' | sed 's/^/"/;s/$/"/' | tr "\n" ","`;
                  export TF_CONFIG={\"cluster\":{\"ps\":[${PS_HOST}],\"worker\":[${WORKER_HOST}]},\"task\":{\"type\":\"worker\",\"index\":${VK_TASK_INDEX}},\"environment\":\"cloud\"};
                  python /var/tf_dist_mnist/dist_mnist.py
              image: volcanosh/dist-mnist-tf-example:0.0.1
              name: tensorflow
              ports:
                - containerPort: 2222
                  name: tfjob-port
              resources: {}
          restartPolicy: Never

Note:

When config env plugin in the tensorflow job above, all the pods will have 2 environment variables VK_TASK_INDEX and VC_TASK_INDEX. The environment variables registered in the ps pod are as follows.
```
[root@tensorflow-dist-mnist-ps-0 /] env | grep TASK_INDEX
VK_TASK_INDEX=0
VC_TASK_INDEX=0
```
Considering the 2 workers, you will get that their names are tensorflow-dist-mnist-worker-0 and tensorflow-dist-mnist-worker-1. And the corresponding values of the index environment variables are 0 and 1.
```
[root@tensorflow-dist-mnist-worker-0 /] env | grep TASK_INDEX
VK_TASK_INDEX=0
VC_TASK_INDEX=0
```
```
[root@tensorflow-dist-mnist-worker-1 /] env | grep TASK_INDEX
VK_TASK_INDEX=1
VC_TASK_INDEX=1
```

Note:

Because of historical reasons, environment variables VK_TASK_INDEX and VC_TASK_INDEX both exist, VK_TASK_INDEX will be deprecated in the future releases.
No value are needed when register env plugin in the volcano job.