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how vc works at woome

A twitter friend has been looking hard at hg and had some questions today about why you would have separate repos for environments (dev, staging, etc...). I am not entirely sure I understood the question but it's probably time to describe how we do things at WooMe.

dev in pieces

WooMe is highly a distributed company. I don't think I can even think of a time when the development team has all been in one place, let alone the management, the product people and the dev team.

Given this we have a distributed model of development. We have a dev system rather like google app engine... We operate a trunk for development in mercurial on a development server hosted on the net. Developers can make remote clones of that with a simple command:

./reponew [ticketnumber|reponame]

any repository with a ticket number is automatically served by our development system as a clone of trunk. So you can make a new repository running live to fix a problem or start working on a feature in seconds.

Say somebody reports bug 4021 to me, I can make a new repo:

$ ssh woomedevserver reponew 4021
4021_fix_bad_bug

It's available immediately as a running instance of our app:

$ curl -i http://4021_fix_bad_bug.woomedevserver/ | |grep HTTP
HTTP/1.1 200 Ok

and I can clone it locally and work on it there of course:

$ hg clone ssh://woomedevserver/ticketrepos/4021_fix_bad_bug 4021_bug
requesting all changes
adding changesets
adding manifests
adding file changes
added 18000 changesets with 406 changes to 101 files
updating to branch default
97 files updated, 0 files merged, 0 files removed, 0 files unresolved

and when I push back to the woomedevserver other people can see my changes and see the effect of the changes in the running instance.

The dev server instances, by the way, are managed by a CGI version of our app (which is based around django) and a path name translating file system to make the repository names legal dns names.

making release

Normally a few things are ready at once. We have an automated tool that makes a release from ticket numbers (our tickets are marked up with repository urls).

We push the merged ticket repos to what we call "running trunk". At this stage running trunk is divergent from trunk by one release candidate.

We do integration testing on running trunk. When it looks good we tag the repo and push the changes to staging.

staging

Our staging environment has the usual job of modelling live. It's not an exact copy since it's all held on only 2 machines. But it's close.

We have about 4 copies of our repository on staging. This is down to the way we configure our app... each instance is a repository and can have local changes (identified by the local directory name).

For example, the bits of the app that serve https pages are in a separate repository so we can configure the instance there to deliver it's static content via https.

When staging contains a release candidate we do regression testing there and once that's passed we push the app to live via a program that knows every live server that should receive a copy.

live

We have something like 20 application servers and 10 database servers. The copy of our code on each of those is a repository and we use mercurial to push to them.

rationale

It occurs to me as I write this that you may be asking 'yes, but why are there all these repos? what purpose do they serve?'

And I guess here we come to it: the reason we have these is that it's my belief that hacking live is necessary sometimes. I do it about twice weekly for one reason or another; there are about 10 of us in the tech team and about half of them are doing the same thing. Using repositories everywhere on live means we can track those changes we're making. You can see really easily when you changed or added a file. When you have something to push across live and back into trunk you can do that the same way you make all the other changes. Some things have to go out as soon as you've fixed them and others can simply go back into trunk and go out with the next release.

So that's why. We're hackers basically, and using repositories makes our lives easier. Why would you not want that?