[LRUG] Puma, CLOSE_WAIT. Arg.

Riccardo Tacconi rtacconi at gmail.com
Thu Feb 18 04:43:29 PST 2016 

Ruby MRI? If yes what's the point of using Puma? With MRI you have one
worker and one thread, which is very inefficient. Would be possible to
split HTTP requests handling from querying the DB? From Puma you could send
requests to a topic (MOM), and multiple workers could process requests and
each worker will have a DB connection. This could work with MRI, although
you will need more RAM. However I would try rubinius of jruby first.

Sorry if I misunderstood, I did not follow the whole thread.

On 18 February 2016 at 12:28, Simon Morley <simon at polkaspots.com> wrote:

> Ruby 2.2.2
> Rails 4.2.5.1
> mysql2 0.4.2 (tried a few)
> Puma 2.16.0
>
>
>
> Simon Morley
>
> Big Chief | PolkaSpots Supafly Wi-Fi
> Bigger Chief | Cucumber Tony
>
> Got an unlicensed Meraki? Set it free with Cucumber
> cucumberwifi.io/meraki
>
>
> On 18 February 2016 at 12:24, Riccardo Tacconi <rtacconi at gmail.com> wrote:
>
>> Which version of Ruby are you using?
>>
>> On 18 February 2016 at 12:17, Simon Morley <simon at polkaspots.com> wrote:
>>
>>> Actually puma docs suggest doing that when using preload_app and
>>> ActiveRecord...
>>>
>>> https://github.com/puma/puma#clustered-mode
>>>
>>>
>>>
>>> Simon Morley
>>>
>>> Big Chief | PolkaSpots Supafly Wi-Fi
>>> Bigger Chief | Cucumber Tony
>>>
>>> Got an unlicensed Meraki? Set it free with Cucumber
>>> cucumberwifi.io/meraki
>>>
>>>
>>> On 18 February 2016 at 12:05, Frederick Cheung <
>>> frederick.cheung at gmail.com> wrote:
>>>
>>>>
>>>>
>>>>
>>>> On 18 February 2016 at 11:17:34, Simon Morley (simon at polkaspots.com)
>>>> wrote:
>>>>
>>>>
>>>> class RadiusDatabase
>>>>   self.abstract_class = true
>>>>   establish_connection "radius_#{Rails.env}".to_sym
>>>> end
>>>>
>>>> class Radacct < RadiusDatabase
>>>> end
>>>>
>>>> Then I decreased our database pool from 20 to 5 and added a
>>>> wait_timeout of 5 (since there seems to be some discrepancies with this).
>>>> Things got much better (but weren't fixed).
>>>>
>>>> I tried querying differently, including using
>>>> connection_pool.with_connection. I've tried closing the connections
>>>> manually and also used ActiveRecord::Base.clear_active_connections!
>>>> periodically. No joy.
>>>>
>>>> By this point, we were running 2-4 instances - handling around very
>>>> little traffic in total (about 50rpm). Every few hours, they'd block, all
>>>> of them. At the same time, we'd see a load of rack timeouts - same DB. I've
>>>> checked the connections - they were each opening only a few to MySQL and
>>>> MySQL was looking good.
>>>>
>>>> One day, by chance, I reduced the 4 instances to 1. *And the problem
>>>> is solved!!! WHAT*? Obviously the problem isn't solved, we can only
>>>> use a single server.
>>>>
>>>>
>>>> Are you using puma in the mode where it forks workers? if so, then you
>>>> want to reconnect post fork or multiple processes will share the same file
>>>> descriptor and really weird shit will happen.
>>>>
>>>> The puma readme advises to do this:
>>>>
>>>> before_fork do
>>>>   ActiveRecord::Base.connection_pool.disconnect!
>>>> end
>>>>
>>>> I don't know off the top of my head whether that  will do the job for
>>>> classes that have established a connection to a different db - presumably
>>>> they have a separate connection pool
>>>>
>>>> Fred
>>>>
>>>> I don't know what's going on here. Have I been staring at this for too
>>>> long (yes)?
>>>>
>>>> Our other servers are chugging along happily now, using a connection
>>>> pool of 20, no errors, no timeouts (different db though).
>>>>
>>>> Has anyone got any suggestions / seen this? Is there something
>>>> fundamentally wrong with the way we're establishing a connection to the
>>>> external dbs? Surely this is MySQL related
>>>>
>>>> Thanks for listening,
>>>>
>>>> S
>>>>
>>>>
>>>> Simon Morley
>>>>
>>>> Got an unlicensed Meraki? Set it free with Cucumber
>>>> cucumberwifi.io/meraki
>>>>
>>>>
>>>> On 15 January 2016 at 13:58, Gerhard Lazu <gerhard at lazu.co.uk> wrote:
>>>>
>>>>> The understanding of difficult problems/bugs and the learning that
>>>>> comes with it cannot be rushed. Each and every one of us has his / her own
>>>>> pace, and all "speeds" are perfectly fine. The only question that really
>>>>> matters is whether it's worth it (a.k.a. the cost of lost opportunity). If
>>>>> the answer is yes, plough on. If not, look for alternatives.
>>>>>
>>>>> Not everyone likes or wants to run their own infrastructure. The
>>>>> monthly savings on the PaaS, IaaS advertised costs are undisputed, but few
>>>>> like to think - never mind talk - about how many hours / days / weeks have
>>>>> been spent debugging obscure problems which "solve themselves" on a managed
>>>>> environment. Don't get me started on those that are building their own
>>>>> Docker-based PaaS-es without even realising it...
>>>>>
>>>>> As a side-note, I've been dealing with a similar TCP-related problem
>>>>> for a while now, so I could empathise with your struggles the second I've
>>>>> seen your post. One of us is bound to solve it first, and I hope it will be
>>>>> you ; )
>>>>>
>>>>> Have a good one, Gerhard.
>>>>>
>>>>> On Fri, Jan 15, 2016 at 10:01 AM, Simon Morley <simon at polkaspots.com>
>>>>> wrote:
>>>>>
>>>>>> You must be more patient that I am. It's been a long month - having
>>>>>> said that, I'm excited to find the cause.
>>>>>>
>>>>>> I misunderstood you re. file descriptors. We checked the kernel
>>>>>> limits / files open on the systems before and during and there's nothing
>>>>>> untoward.
>>>>>>
>>>>>> Since writing in, it's not happened as before - no doubt it'll take
>>>>>> place during our forthcoming office move today.
>>>>>>
>>>>>> I ran a strace (thanks for that suggestion John) on a couple of
>>>>>> processes yesterday and saw redis blocking. Restarted a few redis servers
>>>>>> to see if that helped. Can't be certain yet.
>>>>>>
>>>>>> As soon as it's on, I'll run a tcpdump. How I'd not thought about
>>>>>> that I don't know...
>>>>>>
>>>>>> Actually, this is one thing I dislike about Rails - it's so nice and
>>>>>> easy to do everything, one forgets we're dealing with the real servers /
>>>>>> components / connections. It's too abstract in ways, but that's a whole
>>>>>> other debate :)
>>>>>>
>>>>>> S
>>>>>>
>>>>>>
>>>>>>
>>>>>> Simon Morley
>>>>>>
>>>>>> Big Chief | PolkaSpots Supafly Wi-Fi
>>>>>> Bigger Chief | Cucumber Tony
>>>>>>
>>>>>> simon at PolkaSpots.com
>>>>>> Linkedin: I'm on it again and it still sucks
>>>>>> 020 7183 1471 <020%207183%201471>
>>>>>>
>>>>>> 🚀💥
>>>>>>
>>>>>> On 15 January 2016 at 06:53, Gerhard Lazu <gerhard at lazu.co.uk> wrote:
>>>>>>
>>>>>>> File descriptors, for traditional reasons, include TCP connections.
>>>>>>>
>>>>>>> Are you logging all requests to a central location? When the problem
>>>>>>> occurs, it might help taking a closer look at the type of requests you're
>>>>>>> receiving.
>>>>>>>
>>>>>>> Depending on how long the mischief lasts, a tcpdump to pcap, then
>>>>>>> wireshark might help. Same for an strace on the Puma processes, similar to
>>>>>>> what John suggested . Those are low level tools though, verbose, complex
>>>>>>> and complete, it's easy to get lost unless you know what you're looking for.
>>>>>>>
>>>>>>> In summary, CLOSE_WAITs piling up from haproxy (client role) to Puma
>>>>>>> (server role) indicates the app not closing connections in time (or maybe
>>>>>>> ever) - why? It's a fun one to troubleshoot ; )
>>>>>>>
>>>>>>> On Thu, Jan 14, 2016 at 11:35 PM, Simon Morley <simon at polkaspots.com
>>>>>>> > wrote:
>>>>>>>
>>>>>>>> Right now, none of the servers have any issues. No close_waits.
>>>>>>>>
>>>>>>>> All is well. Seemingly.
>>>>>>>>
>>>>>>>> When it occurs ALL the servers end up going. Sometimes real fast.
>>>>>>>> That's why I thought we had a db bottleneck. It happens pretty quickly,
>>>>>>>> randomly, no particular times.
>>>>>>>>
>>>>>>>> We don't ever really get spikes of traffic, there's an even load
>>>>>>>> inbound throughout.
>>>>>>>>
>>>>>>>> I thought we had someone running a slow loris style attack on us.
>>>>>>>> So I added some rules to HA Proxy and Cloudflare ain't seen nofin honest
>>>>>>>> guv.
>>>>>>>>
>>>>>>>> Will find a way to chart it and send a link over.
>>>>>>>>
>>>>>>>> Will see if we're not closing any files - not much of that going
>>>>>>>> on. There's some manual gzipping happening - we've had that in place for
>>>>>>>> over a year though - not sure why it'd start playing up now. Memory usage
>>>>>>>> is high but consistent and doesn't increase.
>>>>>>>>
>>>>>>>> S
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Simon Morley
>>>>>>>>
>>>>>>>> Big Chief | PolkaSpots Supafly Wi-Fi
>>>>>>>> Bigger Chief | Cucumber Tony
>>>>>>>>
>>>>>>>> simon at PolkaSpots.com
>>>>>>>> Linkedin: I'm on it again and it still sucks
>>>>>>>> 020 7183 1471 <020%207183%201471>
>>>>>>>>
>>>>>>>> 🚀💥
>>>>>>>>
>>>>>>>> On 14 January 2016 at 22:14, Gerhard Lazu <gerhard at lazu.co.uk>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> That sounds like a file descriptor leak. Are the CLOSE_WAITs
>>>>>>>>> growing over time?
>>>>>>>>>
>>>>>>>>> You're right, New Relic is too high level, this is a layer 4-5
>>>>>>>>> issue.
>>>>>>>>>
>>>>>>>>> The simplest thing that can plot some graphs will work. Throw the
>>>>>>>>> dirtiest script together that curls the data out if it comes easy, it
>>>>>>>>> doesn't matter how you get those metrics as long as you have them.
>>>>>>>>>
>>>>>>>>> This is a great blog post opportunity ; )
>>>>>>>>>
>>>>>>>>> On Thu, Jan 14, 2016 at 8:40 PM, Simon Morley <
>>>>>>>>> simon at polkaspots.com> wrote:
>>>>>>>>>
>>>>>>>>>> I would ordinarily agree with you about the connection however
>>>>>>>>>> they hang around for hours sometimes.
>>>>>>>>>>
>>>>>>>>>> The 500 in the hyproxy config was actually left over from a
>>>>>>>>>> previous experiment. Realistically I know they won't cope with that.
>>>>>>>>>>
>>>>>>>>>> Using another server was to find any issues with puma. I'm still
>>>>>>>>>> going to try unicorn just in case.
>>>>>>>>>>
>>>>>>>>>> Will up the numbers too - thanks for that suggestion.
>>>>>>>>>>
>>>>>>>>>> I'll look at a better monitoring tool too. So far new relic
>>>>>>>>>> hasn't helped much.
>>>>>>>>>>
>>>>>>>>>> Thanks
>>>>>>>>>>
>>>>>>>>>> S
>>>>>>>>>>
>>>>>>>>>> Simon Morley
>>>>>>>>>> Big Chief | PolkaSpots Supafly Wi-Fi
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I'm doing it with Cucumber Tony. Are you?
>>>>>>>>>>
>>>>>>>>>> On 14 Jan 2016, at 20:30, Gerhard Lazu <gerhard at lazu.co.uk>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> Hi Simon,
>>>>>>>>>>
>>>>>>>>>> CLOSE_WAIT suggests that Puma is not closing connections fast
>>>>>>>>>> enough. The client has asked for the connection to be closed, but Puma is
>>>>>>>>>> busy.
>>>>>>>>>>
>>>>>>>>>> Quickest win would be to increase your Puma instances. Unicorn
>>>>>>>>>> won't help - or any other Rack web server for the matter.
>>>>>>>>>>
>>>>>>>>>> Based on your numbers, start with 10 Puma instances. Anything
>>>>>>>>>> more than 100 connections for a Rails instance is not realistic. I would
>>>>>>>>>> personally go with 50, just to be safe. I think I saw 500 conns in your
>>>>>>>>>> haproxy config, which is way too optimistic.
>>>>>>>>>>
>>>>>>>>>> You want metrics for detailed CPU usage by process, connections
>>>>>>>>>> open with state by process, and memory usage, by process. Without these,
>>>>>>>>>> you're flying blind. Any suggestions anyone makes without real metrics -
>>>>>>>>>> including myself - are just guesses. You'll get there, but you're making it
>>>>>>>>>> far too difficult for yourself.
>>>>>>>>>>
>>>>>>>>>> Let me know how it goes, Gerhard.
>>>>>>>>>>
>>>>>>>>>> On Thu, Jan 14, 2016 at 3:16 PM, Simon Morley <
>>>>>>>>>> simon at polkaspots.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> Hello All
>>>>>>>>>>>
>>>>>>>>>>> We've been battling with Puma for a long while now, I'm looking
>>>>>>>>>>> for some help / love / attention / advice / anything to prevent further
>>>>>>>>>>> hair loss.
>>>>>>>>>>>
>>>>>>>>>>> We're using it in a reasonably typical Rails 4 application
>>>>>>>>>>> behind Nginx.
>>>>>>>>>>>
>>>>>>>>>>> Over the last 3 months, our requests have gone from 500 rpm to a
>>>>>>>>>>> little over 1000 depending on the hour. Over this period, we've been seeing
>>>>>>>>>>> weird CLOSE_WAIT conns appearing in netstat, which eventually kill the
>>>>>>>>>>> servers.
>>>>>>>>>>>
>>>>>>>>>>> We have 3 Rails servers behind Haproxy running things. Load is
>>>>>>>>>>> generally even.
>>>>>>>>>>>
>>>>>>>>>>> Running netstat on the servers shows a pile of connections in
>>>>>>>>>>> the CLOSE_WAIT state with varying recv-q values as so:
>>>>>>>>>>>
>>>>>>>>>>> tcp      2784    0 localhost:58786         localhost:5100
>>>>>>>>>>>    CLOSE_WAIT
>>>>>>>>>>> tcp      717      0 localhost:35794         localhost:5100
>>>>>>>>>>>    CLOSE_WAIT
>>>>>>>>>>> tcp      784      0 localhost:55712         localhost:5100
>>>>>>>>>>>    CLOSE_WAIT
>>>>>>>>>>> tcp        0        0 localhost:38639         localhost:5100
>>>>>>>>>>>      CLOSE_WAIT
>>>>>>>>>>>
>>>>>>>>>>> That's just a snippet. A wc reveals over 400 of these on each
>>>>>>>>>>> server.
>>>>>>>>>>>
>>>>>>>>>>> Puma is running on port 5100 btw. We've tried puma with multiple
>>>>>>>>>>> threads and a single one - same result. Latest version as of today.
>>>>>>>>>>>
>>>>>>>>>>> I've checked haproxy and don't see much lingering around.
>>>>>>>>>>>
>>>>>>>>>>> Only a kill -9 can stop Puma - otherwise, it says something like
>>>>>>>>>>> 'waiting for requests to finish'
>>>>>>>>>>>
>>>>>>>>>>> I ran GDB to see if I could debug the process however I can't
>>>>>>>>>>> claim I knew what I was looking at. The processes that seemed apparent were
>>>>>>>>>>> event machine and mongo.
>>>>>>>>>>>
>>>>>>>>>>> We then ditched EM (we were using the AMQP gem) in favour of
>>>>>>>>>>> Bunny. That made zero difference.
>>>>>>>>>>>
>>>>>>>>>>> So we upgraded Mongo and Mongoid to the latest versions, neither
>>>>>>>>>>> of which helped.
>>>>>>>>>>>
>>>>>>>>>>> I thought we might have a bottleneck somewhere - Mongo, ES or
>>>>>>>>>>> MySQL. But, none of those services seem to have any issues / latencies.
>>>>>>>>>>>
>>>>>>>>>>> It's also 100% random. Might happen 10 times in an hour, then
>>>>>>>>>>> not at all for a week.
>>>>>>>>>>>
>>>>>>>>>>> The puma issues on github don't shed much light.
>>>>>>>>>>>
>>>>>>>>>>> I don't really know where to turn at the moment or what to do
>>>>>>>>>>> next? I was going to resort back to Unicorn but I don't think the issue is
>>>>>>>>>>> that side and I wanted to fix the problem, not just patch it up.
>>>>>>>>>>>
>>>>>>>>>>> It's starting to look like a nasty in my code somewhere but I
>>>>>>>>>>> don't want to go down that route just yet...
>>>>>>>>>>>
>>>>>>>>>>> Sorry for the long email, thanks in advance. Stuff.
>>>>>>>>>>>
>>>>>>>>>>> I hope someone can help!
>>>>>>>>>>>
>>>>>>>>>>> S
>>>>>>>>>>>
>>>>>>>>>>> Simon Morley
>>>>>>>>>>>
>>>>>>>>>>> Big Chief | PolkaSpots Supafly Wi-Fi
>>>>>>>>>>> Bigger Chief | Cucumber Tony
>>>>>>>>>>>
>>>>>>>>>>> simon at PolkaSpots.com <simon at polkaspots.com>
>>>>>>>>>>> Linkedin: I'm on it again and it still sucks
>>>>>>>>>>> 020 7183 1471 <020%207183%201471>
>>>>>>>>>>>
>>>>>>>>>>> 🚀💥
>>>>>>>>>>>
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>> --
>> Riccardo Tacconi
>>
>> http://github.com/rtacconi
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-- 
Riccardo Tacconi

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