Date: Fri, 21 Aug 2020 19:15:07 +0100
From: Natanael Copa <ncopa@alpinelinux.org>
To: =?UTF-8?B?U8O2cmVu?= Tempel <soeren@soeren-tempel.net>
Cc: ~alpine/devel@lists.alpinelinux.org
Subject: Re: Use of supervise-daemon in Alpine
Message-ID: <20200821191507.7857010b@ncopa-macbook.copa.dup.pw>
In-Reply-To: <3LLUI2KOULSYM.359WA6HATX45B@8pit.net>
References: <3LLUI2KOULSYM.359WA6HATX45B@8pit.net>
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On Thu, 20 Aug 2020 19:04:45 +0200
S=C3=B6ren Tempel <soeren@soeren-tempel.net> wrote:

> Hello,
>=20
> OpenRC ships a program called supervise-daemon(8) which is capable of
> starting daemons and restarting them if they crash. Contrary to
> start-stop-daemon, it does not rely on PID files instead the started
> daemon is a child process of supervise-daemon.
>=20
> Some Alpine OpenRC services already use supervise-daemon(8) (e.g.
> unbound, xdm, wpa_supplicant, =E2=80=A6). I was recently wondering if we =
want to
> migrate busybox-initscripts to using supervise-daemon too and was
> pointed to some comments in the GitLab issue tracker which critique use
> of supervise-daemon for busybox-initscripts because of concern over
> memory usage [0]. Upon further discussion in the IRC some people also
> expressed discomfort in regards to the automatic restarting of crashed
> services (=E2=80=9Cyou don't want to mask crashes=E2=80=9D).

I think it would be nice if we could have the autorestart be
configurable, and let it be off by default.

> However, the primary benefit I personally see with widespread use of
> supervise-daemon is that it would allow us to get rid of racy PID files.
> I would therefore propose that we enable supervise-daemon whenever
> possible in existing OpenRC services (including busybox-initscripts).
> In any case it would be nice to clarify when using supervisor-daemon is
> encouraged (see existing examples above) and when it isn't.

Are there any history of problems with racy pids with busybox
initscripts?

The idea with Alpine has been that the requirements for a minimal
install should be *minimal*, but users can opt-in to use more
convenient tools and services that consumes more resources.

So when there is a request for a change that affects the minimal
install, I think we should have really good cost vs benefit reasons for
enabling them.

So for busybox-initscripts i'd still prefer avoid the supervise-daemon,
unless it is a common problem that busybox syslog, cron and friends
often crashes or have problems with racy pids.

For other, bigger, add-on services, I don't mind the extra KBs.


> Thoughts?

I'm thinking if it ain't broken, don't fix it. At leasts for the
busybox-initscripts.

> Greetings,
> S=C3=B6ren
>=20
> [0]: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/1363#n=
ote_56289