Windows Web Deployment:

Everything you wanted to know,
but were to horrified to ask!

Christopher Lambacher
KCL Custom Software
@lambacck

Why would you subject yourself to this torture?

You like pain!

You want to be different than the cool Python kids?

Your IT department tells you that this is a MICROSOFT shop?

You have 200,000 lines of Classic ASP that you need to port!

In 2010, a non-profit we develop for received grant funding to move their large Classic ASP application into something more sustainable. Unfortunately, in the 2 years between the original grant application and when it was approved, the application had grown so large that it could no longer be fully converted using the grant funds. Luckily, we discovered ways to help us do the port slowly. Part of the application is now fully ported into Pyramid, but there is still a large body of code in Classic ASP. We have a common Python library used by both the Classic ASP and Pyramid-based parts of the application that handles various kinds of shared functionality including security and overall page layout.

First Rule Of Deployment Club

Make your application work first,
then work on deployment!

Deployment Models

Embed in Web Server
Reverse Proxy
Expose your development server

Web Servers

Front End
WSGI

Front End

IIS
Apache
NGINX

WSGI HTTP Servers

Paste serve (no Python 3)
Waitress
CherryPy
Twisted (no Python 3… yet)
POSIX only:
- uWSGI
- Gunicorn
- Spawning
- etc...

Here are a few examples of WSGI servers. Any one of these may work for you in a reverse proxy deployment model. If your framework (cough Django) uses something different, that could work too.

Paste used to be the default server for the Pylons, Pyramid and Turbogears 2 frameworks, but it does not have Python 3 support. Waitress is the development server that ships with Pyramid ever since Pyramid grew Python 3 support.

CherryPy has a well-regarded server of this type. Twisted also has a good WSGI server that can push requests back to a thread pool so that it looks like any of these other servers.

There are a number of other popular options out there in this space that are not Windows compatible. They use fork and signals to do the nice things they do, which Windows doesn't support. It's a pity I can't use them - they look nifty.

Embed In Server Deployment

Web server manages processes
Web server manages communication
Lower communication overhead (maybe)

Apache

mod_wsgi

IIS

Reverse proxy

Load balancing with multiple processes
Merge multiple applications into one
Greater process and threading model control

Apache

Comes Fully Loaded

IIS

Needs Some Help

IIS 7+ has official MS extensions
Older versions take more work or $
- Ionic's Isapi Rewrite Filter (IIRF)
- HeliconTech

IIS on the other hand, needs some help. If you are on IIS 7 or later, there are extensions from Microsoft that can be bent into a reverse proxy setup.

If you are using an older version of IIS, or just like the solution better, you can use the open source Ionic's Isapi Rewrite Filter which also has reverse proxy. HeliconTech also has for-pay options.

This list of tools is non-exhaustive. I'm sure there are other options if these don't appeal to you.

Windows Services

Pure Python

Console Application Wrappers

If you are working with a reverse proxy or running your development server and you want your application to start along with the server, then you need a service.

You can create your own services in python with PyWin32. WsgiSvc is a convenient wrapper (or at least starting point) for paste-deploy based applications that you want to run in a Windows service.

You can also wrap a command line application with srvany or srvstart. Srvany is from Microsoft. srvstart is much more powerful, and allows separate commands for start and stop events.

Fork

It seems like people who start on a POSIX system think that fork is the solution to every process problem. Please, if you are writing new tools, Python has subprocess to manage new processes in a way that works cross-platform. I'd also like to see tools using Multiprocessing, though I don't think this is going to provide good solutions for windows until people move to Python 3. There seems to be some problems with Python2 and Windows and sharing sockets between processes.

Signals

Packaging

pip
- only installs packages from source, so you also need a compiler
- wheel package format may fix that soon
easy_install
- has fewer niceties, but supports binary packages
- will work for now!
Be careful about combining pip and easy_install, they handle namespace packages differently and can get in each others way

Many people beat the “use pip” drum for installing packages. They are not wrong, except that they are. As soon as you need a C extension, you run into problems because pip only installs packages from source so you need a compiler.

Some python developers don't know anything about C and compilers and linkers. Trying to give them succinct instructions about getting those things installed on Windows in the right version for their particular installed version of Python is hard. Oh, and installing Visual Studio on a production server. It's madness. Better stick to easy_install: it will "just work" with the pre-compiled version that the package author provided, even the windows installer exes.

Also look for the wheel package format. It is in the process of being standardized and there is an experimental version of pip with support. Hopefully we'll start seeing this in use soon.

I have sometimes combined the wonders of pip and easy_install, but it is dangerous. If you install packages that share a namespace with the two different tools, you are going to run into import problems. Best not to mix them no matter how tempting, but if you must, force an import of the easy_installed package first. That often makes things work.

py2exe

py2exe gives you an executable that runs one Python program
Does not always play nice setuptools/distribute and entry points
Avoid problems by putting your package on the file system and not in the provided library.zip

If you are writing something to be installed by someone else, you might want to cut down on the dependencies they need to install by using py2exe. py2exe can be finicky with eggs (that's what easy_install installs) and you might have problems with entry points because they won't actually be eggs any more. I have had success by excluding packages from the zip it creates for its code library, and shipping an egg directory for the main application.

Virtualenv

Virtual Envrionments: use them!
Nicer to use with virtualenvwrapper… which is *nix only ☹
- virtualenvwrapper-win: a port to .bat scripts
- virtualenvwrapper-powershell: a port to PowerShell
Use the activate_this script to activate in a service (or Classic ASP)

virtualenv helps you to keep applications with different dependencies from stepping on each other’s toes through the creation of virtual python environments. You should use them. They are even nicer with virtualenvwrapper, which provides a bunch of helpers that make activating, creating, deleting and otherwise managing environments really easy. The original virtualenvwrapper is in bash scripts - so not very useful from the Windows command prompt. Luckily there are a couple of ports, one to batch scripts, and one to PowerShell.

You can also use activate_this to enable a virtualenv from running code. Run it as early as you can after your process starts, for instance when your pywin32 based service first starts up, and make sure it is run before importing the rest of your application.

Temporary Key Value Stores

This is one of the harder problems to solve…
Memcached is installed as part of a Couchbase install, but it is essential to do connection pooling on a high traffic site
Redis has no production ready Windows support
We Use Redis in a Linux VM, hosted on a Windows server

Caching and sessions are often stored in memory-based key value stores, most commonly Memcached and Redis. You can get Memcached installed when you install the community version of Couchbase, and it comes with a nice monitoring application, but I found that the Memcached libraries that were compatible with Windows masked connection errors with key not found (i.e. None). If you have a reasonably high amount of traffic, you want a connection pool. Redis clients have a connection pool, but there is no production-ready Redis port for Windows.

After Memcached became overwhelmed by our increasing traffic load, our solution was to put Redis in Linux on a VM. After moving to Redis, we started getting errors that we tracked down to being a problem with opening too many connections to Redis too quickly. Windows by default has a low limit on the number of outgoing connections it can initiate and our request rate + the TIME_WAIT Delay meant that these ports were being exhausted when attempting to connect to the Memcached or Redis servers. We ended up staying with Redis since it came with a connection pool that limited the number of open connections to a reasonable level.

A dirty little secret: the Redis Virtual Machine is running on the web box, and the load is insignificant at only 1 or 2 percent CPU under heavy traffic.

Questions?

Christopher Lambacher
whatschrisdoing.com
KCL Custom Software
kclsoftware.com
@lambacck

Extra Resources

Unofficial Windows Binaries for Python Extension Packages
bpython works on Windows with the ncurses download from the site above
My tests with multiprocessing and sharing sockets between processes: Works on py3 not on py2

Picture Credits

Tough Cat Eats Pain For Breakfast:
http://cheezburger.com/570458880
One Of These Things Is Not Like The Others:
http://cheezburger.com/3297005312
Microsoft Store:
http://gizmodo.com
Old Dog New Tricks Philosoraptor:
http://www.quickmeme.com/meme/35o4c5/
I Don't Always Deploy Software:
http://memegenerator.net/instance/29594266

More Picture Credits

Crazy Swiss Army Knife:
http://8bit.io/frustrate/
The One Ring:
http://lotr.wikia.com/wiki/One_Ring
Problems:
http://despair.com/problems.html
Tux Fork:
http://www.yolinux.com/TUTORIALS/ForkExecProcesses.html
It's A Trap:
http://knowyourmeme.com/memes/its-a-trap

Windows Web Deployment:

Everything you wanted to know,but were to horrified to ask!

Why would you subject yourself to this torture?

You like pain!

You want to be different than the cool Python kids?

Your IT department tells you that this is a MICROSOFT shop?

You have 200,000 lines of Classic ASP that you need to port!

First Rule Of Deployment Club

Deployment Models

Web Servers

Front End

WSGI HTTP Servers

Embed In Server Deployment

Apache

IIS

Reverse proxy

Apache

IIS

Windows Services

Pure Python

Console Application Wrappers

Fork

Signals

Packaging

py2exe

Virtualenv

Temporary Key Value Stores

Questions?

Extra Resources

Picture Credits

More Picture Credits

Everything you wanted to know,
but were to horrified to ask!