Update PublicPairedSingleSampleWf options.json to include other us-central1 zones

[mbookman]

PublicPairedSingleSampleWf_160927.options.json only includes 2 of the 4 us-central1 zones:

    "zones": "us-central1-b us-central1-c"

I'm not sure if there is a rational for limiting the zones that Cromwell can use to run tasks. The 4 Compute Engine zones in us-central1 are:

• us-central1-a
• us-central1-c
• us-central1-b
• us-central1-f

[vdauwera]

I'm not aware of any rationale, but we should check with the Cromwell team just in case. @knoblett, could you please ask red team?

[ruchim]

Hey all, Cromwell doesn't restrict the usage of any particular zones.

[sooheelee]

When you specify multiple zones, then how is a zone picked for running processes?

[mbookman]

The zone is selected by the Pipelines API at random from the list.

[sooheelee]

Does this reduce the probability of preemption if using preemptible instances? I recall hearing that we pick our central zone to reduce the possibility of preemption.

[mbookman]

That is the expectation.

[sooheelee]

Great. Thanks for clarifying.