Use digest instead of tag so VM uses right image.

[jdangerx]

Overview

Follow-up to #3195 ; Related to #3140 .

We were getting inconsistent behavior pulling the latest image for a certain tag off of Dockerhub - often we would get an out-of-date image running on the VM.

While investigating Google Batch, I found that this was due to Dockerhub not updating its tag references quickly enough. However, we can just refer to the actual image digest we just built, which is unambiguously the correct image.

Given how small this change is, I decided to pull this logic over to the non-Batch world as well, so we don't have to wait for me to get all the Batch stuff working.

Testing

I short-circuited gcp_pudl_etl.sh and had it echo a short message to the logs.

Then:

1. change the line
2. push
3. run build-deploy-pudl.yml
4. observe that the output includes the changed line!

Then, I went back to how it works on main/dev now - using the branch name as the image tag, instead of the image digest. Repeating the flow above updated the changed line on the first iteration, but subsequent changes were not picked up.

So I'm convinced that this should alleviate our "VM doesn't pick up the latest image version" woes.

To-do list

Beta Give feedback

1. Manual testing detailed above
2. Review the PR yourself and call out any questions or issues you have

[jdangerx]

When this gets merged we should probably merge it all the way down to main.

[bendnorman]

Great! Using the digest seems like a better way to ensure we're pulling the correct image.

Seems weird that there is a delay between the image getting uploaded and the digest updating. I'm assuming there are plenty of systems that pull images as soon as they are uploaded.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2f67c05) 92.6% compared to head (46594a7) 92.6%.
Report is 2 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##             dev   #3206     +/-   ##
=======================================
- Coverage   92.6%   92.6%   -0.0%     
=======================================
  Files        140     140             
  Lines      12841   12841             
=======================================
- Hits       11894   11892      -2     
- Misses       947     949      +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[zaneselvans]

I think @jdangerx has gone AFK for the night and it would be great to get this integrated with the other nightly build stuff that was merged today so I'm going to push the button.