Another fascinating topic for you – build versioning! Ok, fun it might not be, but it is important and mostly unavoidable. In an earlier blog I outlined a build versioning strategy I was proposing to use with our Java builds. Since then, the requirements have changed, as they tend to, and so I’ve had to change the versioning convention.
Essentially, what I’m after is a way of using artifact version numbers to tell me some useful at-a-glance information about the artifact I have created. Also, customers want the version number to meet their expectations – that is, when they get a new build, they want to see an easily identifiable difference in the version number between the new build and their old one. What they don’t want is a long complicated list of numbers which are hard to distinguish. For instance, it’s much easy to identify which of the following 2 versions is the latest:
- 5.0.1
- 5.0.4
but it’s not so easy to work out which of these is the latest:
- 5.0.1.13573
- 5.0.1.13753
As we’re practicing continuous delivery, any given check-in can feasibly produce a release build. So, I would like some way of identifying exactly which check in produced my builds, or at least have a way of working out which bits of source code went into my released package. There are a couple of ways we can do this:
Tag the source code – We could make the builds tag the source code in our SCM system (Perforce) with every build. This is relatively easy to do using Ant and Maven. With Ant there are numerous different ways of doing it depending on your SCM system, for instance, with subversion you need to use the SvnAnt tasks from subclipse (http://subclipse.tigris.org/svnant/svn.html) and basically perform a copy of your source url:
<copy srcUrl=”${src.url}” destUrl=”${dest.url}” message=”${version.num}”/>
(this is because tags in svn are just cheap copies with a label).
With Maven you just need to use the release plugin – this automatically handles tagging for you.
Tagging the source code is great – it keeps the version numbers as simple as I’d like, and it’s nicely traceable. However, it’s time consuming, and can result in a lot of tags. The other problem is, I can’t tell which check-in caused the build just by looking at the version number of an artifact.
Use the commit number in the build version - We use a build version of Major.Release.Patch-Build in our artifacts. The build number used to be an auto-incrementing number – this worked fine but it didn’t give us a link back to which commit had caused the build to be made. So, I decided to use the perforce changelist id (i.e. the commit version) as the build number in the version, so that builds would end up looking something like this: 1.0.0-11531.
The problem here is that the version number is not customer friendly – so I remove the build number as a final step, before the builds get released to customers. To track what version the customers have got, I still keep a record of the full build number (including the commit number) in the release notes, and I could also easily inject it into an assembly info or properties/config file if I so wished, so that customers could very easily read out the full version number just by looking in a menu somewhere.
There were several obstacles I had to overcome to get this working. The first obstacle, and really this was the one that stopped me from tagging the source code, was that the maven release plugin is abysmal when it comes to continuous delivery. I needed to use the release plugin to tag the source code, but one of the other things that the maven release plugin does is to remove the word SNAPSHOT, increment the version number, and check the pom back into source control. This would cause another build to trigger in the CI system, which in turn would increment the build number etc and cause another build to trigger – so on and so on. Basically it would create a continually building project.
So I have decided not to use the maven release plugin at all – it doesn’t seem to fit in with Continuous Delivery. In order to create potential release candidates with every successful build, I’ve removed the word SNAPSHOT from all the poms, so we aren’t making any snapshot builds anymore either (except when you build locally – more on that later). The version in the poms now takes the P4 commit number, which is injected via the Continuous Integration system, which in my case is Go. Jenkins also supports this, using the subversion plugin (if you use subversion), which sets an environment variable with the svn revision number (more details here). The Jenkins Perforce plugin does the same thing, setting the P4_CHANGELIST environment variable – so it can easily be consumed (more details here).
Go takes the P4 changelist number and puts it in an environment variable called “GO_PIPELINE_LABEL”. I read this variable in, and assign it to a property called p4.revision. I do this in the command that kicks off the build, so that it overwrites a default value which I can keep in my pom – this is useful because it means my colleagues and I don’t have to make any changes to the pom if we want to run a build locally (bear in mind if we run it locally this environment variable won’t exist on our PCs, so the build would otherwise fail). Here’s a basic run down of a sample pom, with more details to follow:
<modelVersion>4.0.0</modelVersion>
<groupId>etc.so.forth</groupId>
<artifactId>MyArtifact</artifactId>
<packaging>jar</packaging>
<version>${main.version}-${build.number}</version><description>Description about this application</description>
<properties>
<p4.revision>SNAP</p4.revision>
<build.number>${p4.revision}</build.number>
<main.version>5.0.2</main.version>
</properties><scm>
…
</scm><repositories>
<repository>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>release-candidate-repo</id>
<url>http://artifactory.me.com/my-rc</url>
</repository>
</repositories><build>
…
</build>
</project>
The value for p4.revision is “SNAP” by default, meaning that if I make a local build, I’ll get an artifact with the version 5.0.2-SNAP. I know that these builds should never be promoted to production or handed to customers because the word SNAP gives it away. However, when a build is created by the CI system, the following command is passed:
clean deploy sonar:sonar -Dp4.revision=${env.GO_PIPELINE_LABEL}
This overwrites the value for p4.revision, passing in the Perforce commit number, and the build will create something like 5.0.2-1234 (where 1234 is my imaginary p4 commit number).
I’ve added a property called main.version, which is the same as the full version but without the build number. I’ve done this so that I can package up my customer builds (ina zip) and label them with the version 5.0.2. After all, customers don’t care about the build number.
An important policy to follow is once a build is released to a customer, one of the other version numbers MUST be increased, meaning all further builds will be at least 5.0.3. The decision of which version number to increase depends on various business factors – I like to increase the 3rd number if I’m releasing a patch to a previously released build. If I’m releasing new functionality I increase the second number. The first number gets increased for major releases. The whole issue of version numbers becomes a lot less complicated if you’re in the business of releasing software to web servers and you don’t actually have to hand software over to customers. In this instance, I just keep the full version number with the build number at the end, as it’s usually someone like me who has to look after the production system anyway!
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