thanks to ted's documenting sccache support for gcp in bug 1529951, comment 11, it might be simple to enable sccache on windows gcp builders.

let's give it a shot.

the windows gcp builders now have all the pieces required to use sccache

• buckets exist ccgc/storage/browser
• iam level 1, 2 & 3 roles exist and are applied to the workers when provisioned
  next step is to attempt some try pushes where we make use of ted's step 1 instructions in bug 1529951, comment 11.

this change comprises the in-tree changes required to make use of sccache in gcp.
specifically:

• a gcp metadata lookup for availability-zone is added to mozconfig, enabling a build to determine its regional gcp sccache bucket
• the sccache cargo build command is modified to include the gcs feature when the environment contains gcs configuration

note that further changes are required on infra to support sccache use. the required changes already exist and are enabled for gcp windows infra, including:

• a json credential file on the build instance filesystem, containing credentials valid for the appropriate scm level bucket for the gcp region
• an SCCACHE_GCS_KEY_PATH env variable containing the path to the json credential file
• an SCCACHE_GCS_RW_MODE env variable containg the text READ_WRITE
• sccache buckets must exist for each region and scm levels 1 & 3
• credentials for scm level 1 buckets must not be valid for scm level 3 buckets

on gcp systems which do not contain credential files and the above mentioned env variables (eg gecko-[1-3]-b-linux), sccache should fail gracefully without breaking builds.

Comment on attachment 9062135 [details]
enable sccache on gcp

r+ in phabricator

Pushed by cbrindusan@mozilla.com:
https://hg.mozilla.org/integration/autoland/rev/5b08dd3eeec9
enable sccache on gcp r=wcosta

https://hg.mozilla.org/mozilla-central/rev/5b08dd3eeec9