Re: [PATCH v2 1/2] CI: limit GitHub Actions to designated branches

Jeff King [off-list ref] writes:

On Thu, May 07, 2020 at 08:17:27AM -0400, Jeff King wrote:

quoted

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But doesn't this (i.e. uses: actions/github-script) still pay the
cost of spinning up a VM?  How expensive is it to check out a small
tree with a single file, whether it is ref-whitelist or allow-ref?

I suspect this script mechanism may be much cheaper. I don't know the
implementation details, but spinning up a nodejs container to run a
javascript snippet should be much cheaper than a full ubuntu VM running
"git clone" (the clone itself should be super cheap because it's a
shallow single-branch clone of a tree with one file in it, but getting
there is relatively heavy-weight).

Sorry, this is all complete nonsense. There is no magical nodejs
container in Actions. You still have to say "runs-on: ubuntu-latest". So
it's still spinning up that VM and then running inside there.

Ah, I did see "runs-on: ubuntu-latest" in the tutorial for the node
thing, and was very much dissapointed, before I sent that "don't you
still spin up a VM anyway?" response.  Glad to know that I wasn't
totally misreading the documentation, and unhappy that there wasn't
a magic bullet after all X-<.

and they took 1, 2, and 3 seconds respectively. They spend 2s getting
the environment set up and the actions loaded. So the API one spent less
than 1s on the network, but the single-file checkout spent slightly
more. Given the timing variations I've seen, I wouldn't be surprised if
it sometimes goes the other way. But even if those numbers are accurate,
I don't think the cost difference is enough to force our hand either
way.

Yup, the above tempts me to say "because we are spinning a VM
anyway, why not just run an end-user supplied script and let it
decide?" would be the best approach.

Unless somebody finds a magic bullet, that is, but unfortunately the
nodejs one does not seem to be one.

Thanks.