Adding small changes to use docker layers for cache

[vsoch]

This pull request will pull sourcecred/sourcecred:latest first and then use the layers for cache as extra build args. @Beanow figured out all the logistics for sourcecred/widgets, and as promised, I'm following up on the merge of #1320.

Signed-off-by: Vanessa Sochat vsochat@stanford.edu

[Beanow]

🤔 still didn't cache. Is :latest that much out of date?

[vsoch]

node:12 was updated a day ago - I can't tell how different it is though, at least from the Docker Hub interface. We'd have to have had a manifest with layers (from before) and now after.

[Beanow]

node:12 was updated a day ago

That would explain. The layer hash is used to see if it needs to be invalidated for caching. How big of a difference doesn't matter.

Still think it's interesting, should we use :dev instead of :latest?
Because :latest here should be actual releases. We'll likely lose out a lot of caching chances especially when package.json or yarn.lock are updated on master.

[vsoch]

I think it we target a more specific version of node:12, we would be more likely to get a cache. That said, if we target a more specific version, we probably won't get the same security updates. So - it's a tradeoff.

[Beanow]

Agreed, I rather build a little longer than miss out on security updates.

So thinking about :dev to cache from a little more, we have these 3 build filters:

• master
• tag releases
• other branches

master and tag releases should benefit from :dev
Other branches however runs most often and may sometimes not benefit, but most of the time will.

Main situations other branches wouldn't benefit I think.
When master has updated after the branch started. A rebase would fix that.
Or when the branch is not based off of master at all, for example a stable branch to maintain the previous major version. (Which we don't do)

But it would be a lot better whenever.
Master has updated since the last tag release (a lot of the time).

So I think it would give overall better results.
(Worth keeping in mind for widgets as well, though currently :latest and :dev are identical there)

[vsoch]

okay so just to verify - you want to pull dev, to be added (used for cache) to build tag and master releases?

[Beanow]

I think it should be all 3 on dev. So it can replace the :latest pull.

[vsoch]

"latest" changed to "dev"

[Beanow]

Updated my comment for the record to avoid confusion. I think the other branches benefits a lot from :dev.

[teamdandelion]

merged from @Beanow's approval. thanks! :)