Mount input-artifacts into initContainers

[djmcgreal-cc]

Summary

Currently initContainers can't access input: artifacts.

Workaround:

    podSpecPatch: | #can't specify it directly because then it fails validation
      initContainers:
        - name: summation
          volumeMounts:
            - mountPath: /data
              name: input-artifacts #have to manually add the data directory to initContainers, unfortunately - hope Argo don't change their internals on this
              subPath: data

Given the structure of the Workflow yaml, I'd naturally assumed that the input-artifacts would be mounted into initContainers also.

Use Cases

Due to a lack of a when clause on output artifacts I have a initContainer doing the real work which needs the artifacts and a container whose code conditionally copies them to a different file path and then making the artifacts optional.

I also commonly use an initContainer pattern as storage is difficult in EKS where we can't assume Workflow Pods will be scheduled in the same availability zone to use EBS backed PVCs.

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