From: Eric Wong <firstname.lastname@example.org>
To: Sam Saffron <email@example.com>
Subject: Re: Auto scaling workers with unicorn
Date: Tue, 5 Dec 2017 01:51:58 +0000 [thread overview]
Message-ID: <20171205015158.GA2540@starla> (raw)
Sam Saffron <firstname.lastname@example.org> wrote:
> I would like to amend Discourse so we "automatically" absorb certain
> traffic spikes. As it stands we can only configure unicorn with
> num_workers and use TTIN and TTOUT to tune the number on the fly.
> I was wondering if you would be open to patching unicorn to allow it
> to perform auto-tuning based on raindrops info.
I'm no fan of this or auto-tuning systems in general.
More explanation below.
> How it could work
> 1. configure unicorn with min_workers, max_workers, wince_delay, scale_up_delay
> 2. If queued requests is over 0 for N samples over scale_up_delay, add
> a worker up until max_workers
> 3. If queued requests is 0 for N samples over wince_delay scale down
> until you reach min workers
This adds more complexity to configuration: increasing the
likelyhood of getting these numbers completely wrong. GC and
malloc tuning is tricky and error-prone enough, already.
Mainly, this tends to hide problems for later; instead of
forcing you to deal with your resource limitations up front.
It becomes more difficult to forsee resource limitations down
the line. Before I worked on unicorn, I've seen auto-scaling
Apache workers mistuned far too often and running out of DB
connections or memory; and that happens at the worst time:
when your site is under heavy load (when you have the most to
lose (or gain)).
> Having this system in place can heavily optimize memory in large
> deployments and simplifies provisioning logic quite a lot.
My philosophy remains to tune for the worst case possible.
If you really need to do something like run an expensive
off-peak cronjob, maybe have it TTIN at the beginning and TTOU
again at the end.
Fwiw, the most useful thing I've found TTIN/TTOU for is cutting
down to one worker so I know which one to strace when tracking
down a problem; not auto-scaling.
> Wondering what you think about this and if you think unicorn should
> provide this option?
Fwiw, my position has been consistent on this throughout the years.
Also, digging through the archives, Ben Somers came up with
alicorn a while back and it might be up your alley:
next prev parent reply other threads:[~2017-12-05 1:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-04 23:42 Auto scaling workers with unicorn Sam Saffron
2017-12-05 1:51 ` Eric Wong [this message]
2017-12-05 2:33 ` Ben Somers
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