Add placement tag override on base template

[datianshi]

This is just change the base spiff template diego.yml

So user can provide stub to override/add isolation segments tag

[cfdreddbot]

Hey datianshi!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/140929693

The labels on this github issue will be updated when the story is started.

[emalm]

Hi, @datianshi, could you elaborate on how you plan to use a Diego deployment with placement tags configured for isolation segments? We haven't made placement tags configurable on the manifest-generation templates because there's only one set of cell jobs in the manifest, so if that set of jobs received a non-empty placement-tag set then there would be no untagged set of cells to accept CF work in the "default" isolation segment.

Thanks,
Eric, CF Diego PM

[datianshi]

@ematpl By default it is still empty... but it opens the possibility to override one AZ cell to have the placement tags without touching the template files. To me it at least give end user both flexibility and education purpose on reading the templates....

[emalm]

Thanks for the context, @datianshi. Although it might be convenient for experimentation, I'm hesitant to recommend conflating AZs with isolation segments, and I'd rather have the set of placement tags apply to all 3 AZ-specific cell jobs. One deployment strategy that could work would be to use the manifest-generation scripts to produce a cell-only manifest, all the cells of which have the set of placement tags for the desired isolation segment. That would likely require a different subnet per AZ for those cells (or would require configuring mutually exclusive IP ranges within the same IaaS subnets), in order to prevent BOSH from assigning conflicting IP addresses.

In any case, I think we would accept a PR that took a new optional value in the property-overrides stub (say, property_overrides.rep.placement_tags) and applied it to all 3 cell jobs in the manifest, defaulting to a null value.

Thanks again,
Eric

[emalm]

Hey @datianshi, any interest in making the proposed change to the PR?

Thanks,
Eric

[datianshi]

@ematpl It makes sense and made the change. Sorry missed that one month ago message

-Shaozhen

[datianshi]

Just squashed the multiple commits

[emalm]

Thanks, @datianshi! Prioritized for the Diego team to review.

Best,
Eric