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

From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: "Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Taylor Blau" <me@ttaylorr.com>,
	"Đoàn Trần Công Danh" <congdanhqx@gmail.com>,
	git@vger.kernel.org, "Jeff Hostetler" <jeffhost@microsoft.com>
Subject: Re: [PATCH v2 1/2] CI: limit GitHub Actions to designated branches
Date: Thu, 07 May 2020 11:17:50 -0700	[thread overview]
Message-ID: <xmqqimh74njl.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20200507140208.GA3060463@coredump.intra.peff.net> (Jeff King's message of "Thu, 7 May 2020 10:02:08 -0400")

Jeff King <peff@peff.net> writes:

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