Perfect Deployment Of Websites

Recently I have been giving a lot of thought to how best to deploy websites, specifically Django powered sites. In future posts I’ll describe how I use some of tools available to deploy websites, but in this post I want to set out the goals of any system that you use to deploy a website.

What do mean when we say deployment? Clearly it involves getting your code onto a production server but the process also needs to look after any dependencies of your code. Updates also sometimes require database changes and these need to be managed and deployed with the appropriate code changes. If your website is more than just a hobby then it will also usually involve some sort of high availably set up.

The first requirement is repeatability. You might be able to follow a list of ten commands without making a mistake normally, when your site is broken and you need to get a fix deployment as soon as possible following that list will suddenly become a whole lot harder. For this reason, and to avoid the temptation to cut corners when deploying a change automation of as much as possible is key.

The second requirement is scalability. As your website grows you deployment process needs to be able grow with it. As you add a new server to your cluster you don’t want to have to spend a long time updating your deployment process, nor do you want the extra server to create extra work for you to do on every deployment.

Another requirement is speed. I’m usually very skeptical of anything that claims ‘written for speed’ as a key benefit. Unless you know something is slow, it’s usually better to make something easier to maintain than quick. An automatic process will inevitably be quicker than a manual one and whether or not your deployment process results in down time for your site the upgrade process is inevitably a risk and ideally that risk window will be kept to a minimum.

Database migrations are a tricky thing to get right. A deployment system must allow developers to track changes that they make to the database, and to make it easy to ensure these changes are applied at the right moment.

In future posts I will talk about how tools such as fabric, virtualenv, pip and south can be used to meet these requirements and ensure you never have a failed deployment again.

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Author: Andrew Wilkinson

I'm a computer programmer and team leader working at the UK grocer and tech company, Ocado Technology. I mostly write multithreaded real time systems in Java, but in the past I've worked with C#, C++ and Python.

5 thoughts on “Perfect Deployment Of Websites”

  1. One of Joel Spolsky’s list of things to look for in a potential good-quality employer is whether they have a single-line deployment process. I’ve never seen one in practice!

  2. I agree with Joel on this point – a single line deployment process definitely indicates that an appropriate amount of time has been spent on tools and processes, rather than just getting the code written.

    For a website written in a scripting language a single line deployment process shouldn’t be too hard. If something requires building or packaging then it’s harder, but still far from impossible.

  3. for personal projects, I have something like
    $ fab push:syncdb=1,pip=1

    which does bzr push to the remote host, bzr update over there, etc (syncdb –migrate and pip being optional)

    for initial deployment I do
    $ fab setup

    … which kinda feels like working through the exhaust to change the oil 😀

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