Bug#727708: Problems with upstarts event model
Hi,
I just want to raise one issue that I think has not been adequately
addressed by any of the position statements (it has unfortunately been
deleted from the upstart page and been trimmed down a lot on the systemd
page):
I think an important drawback of upstart is the idea of treating
dependencies as events.
The systemd statement already mentions correctly that upstart turns the
dependency chain “upside down”, because it starts a service as soon as
all its dependencies are ready, instead of starting the dependencies of
a service when the service itself should be started.
This has practical implications as well. When trying to debug why a
service isn't starting, it's simpler to investigate which dependency
couldn't be started than to figure out which event was not emitted for
what reason at some point in the past.
Moreover (and, in my opinion, most importantly), by treating
dependencies as events ("start A if B has started" rather than the
conventional "A requires B"), native upstart jobs can create "event
loops" which can block starting of all services in the loop. Example:
https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/964207 and
discussion at https://lists.debian.org/debian-devel/2013/05/msg01500.html
As far as I can tell, something like this can not happen with systemd units.
Best,
-Nikolaus
--
Encrypted emails preferred.
PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6 02CF A9AD B7F8 AE4E 425C
»Time flies like an arrow, fruit flies like a Banana.«
Reply to: