Django Scaler
=============
**Degrade gracefully by automatically replacing heavy pages with static pages while a server is taking strain.**
.. contents:: Contents
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Installation
------------
#. Install or add ``django-scaler`` to your Python path.
#. Add ``scaler`` to your ``INSTALLED_APPS`` setting.
#. Add ``scaler.middleware.ScalerMiddleware`` to the top of your ``MIDDLEWARE_CLASSES`` setting.
#. Add (r'^scaler/', include('scaler.urls')) to urlpatterns.
Overview
--------
Servers may at times get overloaded due to a variety of reasons. When that
happens you don't want expensive requests to bring down your entire site. The
site must redirect expensive requests to a "server busy" page while the server
is under load, and then automatically remove the redirects once the load has
dropped enough.
`django-scaler` addresses this situation in two ways. Firstly, it knows which
requests to redirect by itself. Secondly, it can be instructed to redirect the
N most expensive requests. It stores response time data in in-memory caches
enabling it to make these decisions.
Usage
-----
Pasted from ``test_settings.py``::
DJANGO_SCALER = {
'server_busy_url_name': 'server-busy',
# How many response times to consider for an URL. A small value means slow
# response times are quickly acted upon, but it may be overly aggressive.
# A large value means an URL must be slow for a number of requests before
# it is acted upon. The default is 100.
'trend_size': 10,
# How much slower than average the trend must be before redirection kicks
# in. The default is 4.0.
'slow_threshold': 2.0,
# How many seconds to keep redirecting an URL before serving normally. The
# default is 60.
'redirect_for': 10,
# A function that returns how many of the slowest URLs must be redirected.
# Depending on the site, data and load on the server this may be a large
# number. This allows external processes to instruct the middleware to
# redirect. The default is 0.
'redirect_n_slowest_function': lambda: 0,
# A function that returns what percentage of the slowest URLs must be
# redirected. Depending on the site, data and load on the server this may
# approach 100. The default is 0.
'redirect_percentage_slowest_function': lambda: 0,
# A function that returns a list of regexes. URLs matching the regexes are
# redirected. Each regex is a simple string. Do not prefix with r''. The
# default is an empty list.
'redirect_regexes_function': lambda: [],
}
Authors
=======
Praekelt Foundation
-------------------
* Hedley Roos
Changelog
=========
0.2
---
#. Regex URL matching for explicit redirection.
#. Percentage slowest explicit redirection.
0.1
---
#. First release.
