Example 3. Reading and Writing Data on a Persistent Volume

Persistent Volumes can obviate the need for data ingress and egress. A persistent volume may already have the data needed to execute a workflow when it is mounted, and data can be written to the volume that will persist after the workflow has completed. In the following example, we mount a persistent volume to the job named new-file. The volume already has the GitHub repo Hello-World saved on it. The job copies the README file to a new file and appends text.

This example assumes that an administrator has already configured a storage provisioner with a persistent volume available to your group.

version: v4
volumes:
  per_vol_1:
    use: my-provisioner
    name: my-persistent-volume
jobs:
  new-file:
    image:
      uri: docker://alpine
    mounts:
      /data: per_vol_1
    cwd: /data/Hello-World-master
    script: |
      #!/bin/sh
      cp README README.new && echo "(goodbye dear basement)" >>README.new
    resource:
      cpu:
        cores: 2
        affinity: NUMA
      memory:
        size: 2GB

The example above uses the V4 syntax. The previous (V1) synstax is still supported for backwards compatibility. In V1, the equivalent syntax would have looked like the following:

volumes:
  per_vol_1:
    reference: volume://user/<storage-class>

See Storage Volumes and Workflows for the full V4 volume syntax.

After the workflow has completed successfully, there is a new file on our persistent volume located at /Hello-world-master/README.new with the following contents:

Hello World!
(goodbye dear basement)