Workers of the world (wide web), unite!

2010/03/27 § 3 Comments

A few days ago I ran into an interesting post by Ian Bicking about a benchmark that Nicholas PiĆ«l ran on WSGI servers. Go ahead and read the original posts, but the the skinny is that Nicholas’ (and many others’) focus was about performance, wherein Ian (and I…) feel more attention should be given to the ‘robustness’ of the server, so to speak.

What’s robustness, really? Well, worker-code can misbehave in a lot of ways (and for a lot of reasons), and a robust server will deal gracefully with these misbehaviours. The puritans in the crowd may well argue that the proper solution is to fix the worker (or any of its hierarchy of dependencies). However, all too often purity is a luxury that a web programmer can’t afford (and maybe shouldn’t bother to afford, but maybe we can talk about that some other time).

So I sat down and jotted something called Labour which is a library/tool to ‘benchmark’ WSGI servers not on the merit of how many jiffies they take to parse HTTP headers and what kind of scheduler algorithm they got, but rather on how they’re handling bad workers (socialist pun intended but not necessarily achieved). Labour lets a test author write elegant (ahem) code to declare a certain mixture of bad worker behaviour, and then run it against any one of several WSGI servers.

Let’s look at the simplest example (you can find a few more in Labour’s repository):

from labour import servers
from labour import client
from labour import behaviours
from labour import report

driver = client.Client()
driver.add_behaviour(behaviours.PlainResponse(), weight=99)
driver.add_behaviour(behaviours.Sleeping(sleep_duration=1),
                     weight=1)

with servers.WSGIRef() as server:
  driver.execute(iterations=1000)

report.trivial_report(driver)

At its current early stage, Labour supports these (self explanatory) behaviours: PlainResponse, Sleeping, IOBound, LeakMemory, PythonWedge and SIGSEGV, more can be added with ease. It also supports the following servers (at least to some extent): WSGIRef, Twisted, CherryPy, Cogen, FAPWS3, Gevent and Paste. Significant work should be done in the areas of forking test clients in parallel (the library is near meaningless without this), supporting more WSGI servers and better exploitation of those already supported, richer and better reporting and cleaning up the potential mess after a test.

This long list of caveats said – it is actually working code and it’s currently on github (link above). So either grab it while it’s hot or follow this space to see updates in the (near) future, I’d love to hear what you think about it.

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