Development with Python

1. What I’m calling a “staging” server, some people would call a “development” server, and some others would

also like to distinguish “preproduction” servers. Whatever we call it, the point is to have somewhere we can

try our code out in an environment that’s as similar as possible to the real production server.

Why not ping me a note once your site is live on the web, and send

me the URL? It always gives me a warm and fuzzy feeling …

TDD and the Danger Areas of Deployment

Deploying a site to a live web server can be a tricky topic. Oft-heard is the forlorn cry

—”

but it works on my machine!

“.

Some of the danger areas of deployment include:

Static files (CSS, JavaScript, images, etc.)

Web servers usually need special configuration for serving these.

The database

There can be permissions and path issues, and we need to be careful about pre‐

serving data between deploys.

Dependencies

We need to make sure that the packages our software relies on are installed on the

server, and have the correct versions.

But there are solutions to all of these. In order:

• Using a

staging site

, on the same infrastructure as the production site, can help us

test out our deployments and get things right before we go to the “real” site.

• We can also

run our functional tests against the staging site

. That will reassure us that

we have the right code and packages on the server, and since we now have a “smoke

test” for our site layout, we’ll know that the CSS is loaded correctly.

•

Virtualenvs

are a useful tool for managing packages and dependencies on amachine

that might be running more than one Python application.

• And finally,

automation, automation, automation

. By using an automated script to

deploy new versions, and by using the same script to deploy to staging and pro‐

duction, we can reassure ourselves that staging is as much like live as possible.

Over the next few pages I’m going to go through

deployment procedure. It isn’t meant

to be the

perfect

deployment procedure, so please don’t take it as being best practice, or

a recommendation—it’s meant to be an illustration, to show the kinds of issues involved

in deployment and where testing fits in.

132

Chapter 8: Testing Deployment Using a Staging Site