This text explains how to configure Nginx and Vaurien to test HTTP client code while avoiding network traffic and introducing simulated delays and errors. This setup is necessary if you want to experiment with the flags2*.py image download examples in this directory -- covered in chapters 17 and 18 of Fluent Python.
The flag download examples are designed to compare the performance of different approaches to finding and downloading files from the Web. However, we don't want to hit a public server with multiple requests per second while testing, and we want to be able to simulate high latency and random network errors.
For this setup I chose Nginx as the HTTP server because it is very fast and easy to configure, and the Vaurien proxy because it was designed by Mozilla to introduce delays and network errors for testing Web services.
The archive flags.zip, contains a directory flags/ with 194 subdirectories, each containing a .gif image and a metadata.json file. These are public-domain images copied from the CIA World Fact Book.
Once these files are unpacked to the flags/ directory and Nginx is configured, you can experiment with the flags2*.py examples without hitting the network.
The instructions in this section are for GNU/Linux or OSX using the command line. Windows users should have no difficulty doing the same operations with the Windows Explorer GUI.
Unpack the initial data in the countries/ directory:
$ unzip flags.zip ... many lines omitted ... creating: flags/zw/ inflating: flags/zw/metadata.json inflating: flags/zw/zw.gif
Verify that 194 directories are created in countries/flags/, each with a .gif and a metadata.json file:
$ ls flags | wc -w 194 $ find flags | grep .gif | wc -l 194 $ find flags | grep .json | wc -l 194 $ ls flags/ad ad.gif metadata.json
Download and install Nginx. I used version 1.6.2 -- the latest stable version as I write this.
- Download page: http://nginx.org/en/download.html
- Beginner's guide: http://nginx.org/en/docs/beginners_guide.html
Edit the the nginx.conf file to set the port and document root. You can determine which nginx.conf is in use by running:
$ nginx -V
The output starts with:
nginx version: nginx/1.6.2 built by clang 6.0 (clang-600.0.51) (based on LLVM 3.5svn) TLS SNI support enabled configure arguments:...
Among the configure arguments you'll see --conf-path=. That's the file you will edit.
Most of the content in nginx.conf is within a block labeled http and enclosed in curly braces. Within that block there can be multiple blocks labeled server. Add another server block like this one:
server {
listen 8001;
location /flags/ {
root /full-path-to.../countries/;
}
}
After editing nginx.conf the server must be started (if it's not running) or told to reload the configuration file:
$ nginx # to start, if necessary $ nginx -s reload # to reload the configuration
To test the configuration, open the URL http://localhost:8001/flags/ad/ad.gif in a browser. You should see the blue, yellow and red flag of Andorra.
If the test fails, please double check the procedure just described and refer to the Nginx documentation.
At this point you may run the flags_*2.py examples against the Nginx install by providing the --server LOCAL command line option. For example:
$ python3 flags2_threadpool.py -s LOCAL LOCAL site: http://localhost:8001/flags Searching for 20 flags: from BD to VN 20 concurrent connections will be used. -------------------- 20 flags downloaded. Elapsed time: 0.09s
Note that Nginx is so fast that you will not see much difference in run time between the sequential and the concurrent versions. For more realistic testing with simulated network lag, we need to set up the Vaurien proxy.
Vaurien depends on gevent which is only available for Python 2.5-2.7. To install Vaurien I opened another shell, created a virtualenv for Python 2.7, and used that environment to install and run the vaurien package:
$ virtualenv-2.7 .env27 --no-site-packages --distribute New python executable in .env27/bin/python Installing setuptools, pip...done. $ . .env27/bin/activate (.env27)$ pip install vaurien Downloading/unpacking vaurien Downloading vaurien-1.9.tar.gz (50kB): 50kB downloaded ...many lines and a few minutes later... Successfully installed vaurien cornice gevent statsd-client vaurienclient greenlet http-parser pyramid simplejson requests zope.interface translationstring PasteDeploy WebOb repoze.lru zope.deprecation venusian Cleaning up...
Using that same shell with the .env27 environment active, run the vaurien_delay.sh script in the countries/ directory:
(.env27)$ $ ./vaurien_delay.sh 2015-02-25 20:20:17 [69124] [INFO] Starting the Chaos TCP Server 2015-02-25 20:20:17 [69124] [INFO] Options: 2015-02-25 20:20:17 [69124] [INFO] * proxies from localhost:8002 to localhost:8001 2015-02-25 20:20:17 [69124] [INFO] * timeout: 30 2015-02-25 20:20:17 [69124] [INFO] * stay_connected: 0 2015-02-25 20:20:17 [69124] [INFO] * pool_max_size: 100 2015-02-25 20:20:17 [69124] [INFO] * pool_timeout: 30 2015-02-25 20:20:17 [69124] [INFO] * async_mode: 1
The vaurien_delay.sh creates an HTTP proxy on port 8002 which adds a 1s delay to every response. You can test it with a browser on port 8002: http://localhost:8002/flags/ad/ad.gif -- the flag of Andorra should appear after 1 second.
There is also the vaurien_error_delay.sh script which runs a proxy on port 8003 producing errors in 25% of the responses and a .5 s delay to 50% of the responses. You can also test it with the browser on port 8003, but rememeber that errors are expected.
Homebrew (copy & paste code at the bottom of http://brew.sh/):
$ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" $ brew doctor $ brew install nginx
Download and unpack:
Docroot is: /usr/local/var/www /usr/local/etc/nginx/nginx.conf
To have launchd start nginx at login:
ln -sfv /usr/local/opt/nginx/*.plist ~/Library/LaunchAgents
Then to load nginx now:
launchctl load ~/Library/LaunchAgents/homebrew.mxcl.nginx.plist
Or, if you don't want/need launchctl, you can just run:
nginx
Docroot is: /usr/share/nginx/html