Learn How Disqus Does 'It' When 'It' Isn't Django

Adam Hitchcock
@NorthIsUp
How DISQUS does ‘it’
when ‘it’ isn’t Django
Tuesday, June 25, 13

we’re hiring
disqus.com/jobs
If this is
interesting to you...

what is DISQUS?

DISQUS sees a lot of traffic
Google Analytics: Feb 2013 - March 2013

what makes up Disqus?

mostly Python

(and javascript)

but mostly Python

and we love it!

why python?
๏ because it is fast…
๏ to develop in
๏ good community
๏ lots of libraries
๏ so active we can’t keep up with it
๏ is anybody using 3.3 yet?
๏ Disqus has a really good dev loop for it

how does our dev loop work?
๏ diff code (with phabricator)
๏ get that reviewed
๏ review with phabricator
๏ ci done by jenkins
๏ land it on master (git push)
๏ wait for the daily deploy (ops team)
๏ and we are moving to autodeploy (we’ll revisit
this one)

break it down.
๏ mostly Django
๏ two years ago 95% Django*
๏ today ~70% Django*
๏ what is in that growing gap?
๏ *totally made up numbers

how does this actually work at Disqus?

disqus-web (kinda monolithic)
๏ Django + celery on postgres + rabbit
๏ we roll up commits for a deploy
๏ risk of revert that isn’t your fault
๏ you bring down the whole thing if you
forgot to remove that pdb.settrace()
๏ high scrutiny in code review (see above)
๏ high volume of code review (code review
RTT can be a full day)
๏ lots of legacy code to work around (and
not break)

problems that don’t ﬁt
๏ high concurrency
๏ isolation
๏ feature
๏ failure
๏ speed (cpu cycles)
๏ speed (dev iteration cycle)
๏ fun

what did we play with?

for fun and concurrency!
๏ nginx + nginx-modules
๏ https://speakerdeck.com/northisup/
scaling-realtime-at-disqus?slide=39
๏ nginx + lua
๏ https://github.com/NorthIsUp/nginx-
oauth-on-dotcloud/blob/master/nginx/
access.persona.lua.in
๏ go
๏ http://blog.disqus.com/post/
51155103801/trying-out-this-go-thing

embedly in nginx + lua
local http = require "resty.http"
local cjson = require "cjson"
local url = "https://api.embed.ly/1/oembed?key=" ..
ngx.var.api_key .. "&url=" .. ngx.var.url
local hc = http:new()
local ok, code, headers, status, body = hc:request {
url = url,
method = "GET"
}
if code ~= 200 then
ngx.exit(code)
end
local thumbnail = cjson.decode(body).thumbnail_url
ngx.var.thumbnail = thumbnail

python still works too

isolation and iteration speed
๏ failure should be isolated to a small service
๏ successes should be allowed to occur
quickly
๏ python is still great for these use cases

when we needed it right now!
๏ if __name__ == ‘__main__’:
๏ from wsgiref.simple_server import make_server
๏ from xmlrpclib import ServerProxy

it works great!
๏ for one deploy
๏ then you have to update it…

lessons
๏ consistency is good!
๏ protects you from somebody quitting or
getting hit by a bus
๏ anybody can just pick it up and run
๏ simplicity is good!
๏ modularity is good
๏ the ability to borrow/combine features
from other projects
๏ but copypasta is bad
๏ and not bugging ops for a deploy is the

enter disqus-service

disqus-service
๏ the goal is consistent/free access to…
๏ conﬁg
๏ switches
๏ logging
๏ stats
๏ other systems
๏ and should be easy to run

@service
๏ equivalent to if __name__ == ‘__main__’:
๏ that is basically it, you can now run it

hello.py
from disqus.service.application import
service
@service
def world():
print "hello world"
$ toil run hello.world
hello world

but you want more power
๏ class Service:
๏ @handler
๏ @pre_config
๏ @post_config
๏ @pre_setup
๏ @post_setup
๏ @pre_update_config
๏ @post_update_config

hello-v2.0.py
from disqus.service.application import (Service,
handler, post_config)
def World(Service):
@handler
def world(self):
print self.redis.get("hello world")
@post_config
def setup_redis(self)
self.redis = Redis(
host=self.config.REDIS_HOST,
port=self.config.REDIS_PORT
)
world = World()

mixins!
๏ FlaskService
๏ the service instance is also a wsgi app
๏ GeventService
๏ concurrency helpers
๏ RedisService
๏ KafkaService
๏ DjangoORMService (currently in progress)

real life Disqus code!
from __future__ import absolute_import
from IPython.frontend.terminal.embed import InteractiveShellEmbed
from disqus.service.application import handler
import tempest
from tempest.services.mixins.data import RedisMixin
class Shell(RedisMixin):
@handler
def shell(self, *args, **kwargs):
"""
runs an ipython shell loaded in the tempest module
"""
ipshell = InteractiveShellEmbed()
ipshell(local_ns=locals(), global_ns=globals(), module=tempest)
shell = Shell()

I want to talk more about mixins,
because I really like them.
So the following slides are about
mixins, but not about services.
Please use your imagination that
I did not just copypasta them
from my pycon slides

data pipelines service
class Pipeline(object):
def parse(self, data):
raise NotImplemented('No ParserMixin used')
def compute(self, data, parsed_data):
raise NotImplemented('No ComputeMixin used')
def publish(self, data, parsed_data, computed_data):
raise NotImplemented('No PublisherMixin used')
def handle(self, data):
parsed_data = self.parse(data)
computed_data = self.compute(data, parsed_data)
return self.publish(data, parsed_data, computed_data)

example mixins
class JSONParserMixin(Pipeline):
def parse(self, data):
return json.loads(data)
class AnnomizeDataMixin(Pipeline):
return {}
class SuperSecureEncryptDataMixin(Pipeline):
return parsed_data.encode('rot13')
class HTTPPublisher(Pipeline):
u = urllib2.urlopen(self.dat_url, computed_data)
return u
class FilePublisher(Pipeline):
with open(self.output, 'a') as f:
f.write(computed_data)

final pipeline service
class JSONAnnonHTTPPipeline(
JSONParserMixin,
AnnomizeDataMixin,
HTTPPublisherMixin):
pass
class JSONSecureHTTPPipeline(
JSONParserMixin,
SuperSecureEncyptionMixin,
HTTPPublisherMixin):
pass
class JSONAnnonFilePipeline(
JSONParserMixin,
AnnomizeDataMixin,
FilePublisherMixin):
pass

what about tests?
class JSONAnnonHTTPPipelineTest(
BasePipelineTest,
JSONParserMixinTest,
AnnomizeDataMixinTest,
HTTPPublisherMixinTest):
pass

open source as output
๏ we have lots of open source stuff
๏ sentry for errors
๏ nydus (for redis connections)
๏ django-mailviews
๏ gargoyle (and v2.0 renamed to gutter)
๏ and more! https://github.com/disqus/
๏ not yet for disqus-service
๏ but I want your feedback!
๏ would you use actually it?

psst, we’re hiring
disqus.com/jobs
If this was
interesting to you...

psst, we’re hiring
disqus.com/jobs
meetup.com/ArchCamp
meetup.com/Disqus

What did I just talk about?
๏ Lots of python at Disqus!
๏ But not all of it
๏ because sometimes other tools are better
๏ Services are awesome
๏ Mixins make testing super easy
๏ And we don’t have all the answers...

questions?
๏ How do you run services?
๏ RPC vs HTTP vs Queues (I like queues)
๏ what do you use for highly concurrent
systems?
๏ do you lint for print or pdb.settrace() or
import debug
๏ if yes, can I have it?
๏ dev != prod, or does it?
๏ if you run uwsgi + nginx in prod
๏ why dev with ./manage.py runserver?
@NorthIsUp

Learn How Disqus Does 'It' When 'It' Isn't Django

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Learn How Disqus Does 'It' When 'It' Isn't Django