How might maven's buildNumber metadata become inconsistent across multiple build agents?
- by Brian Laframboise
We recently added a second build machine to our build environment and began experiencing very odd occasional build failures.
I have two separate Maven build machines, A and B, each running Maven 2.2.1 and communicating to a shared Nexus 1.5.0 repository manager. My problem is that builds on B will occasionally fail because it refuses to download a newer version of a common dependency 'acme-1.0.0-SNAPSHOT' previously built by A and uploaded to Nexus.
Looking inside the local repositories on both machines I noticed some oddities in the repository metadata.
Machine A's acme\1.0.0-SNAPSHOT\maven-metadata-nexus.xml:
<metadata>
<groupId>acme</groupId>
<artifactId>acme</artifactId>
<version>1.0.0-SNAPSHOT</version>
<versioning>
<snapshot>
<buildNumber>1</buildNumber>
</snapshot>
<lastUpdated>20100525173546</lastUpdated>
</versioning>
</metadata>
Machine B's acme\1.0.0-SNAPSHOT\maven-metadata-nexus.xml:
<metadata>
<groupId>acme</groupId>
<artifactId>acme</artifactId>
<version>1.0.0-SNAPSHOT</version>
<versioning>
<snapshot>
<buildNumber>2</buildNumber>
</snapshot>
<lastUpdated>20100519232317</lastUpdated>
</versioning>
</metadata>
In Nexus's acme/1.0.0-SNAPSHOT/maven-metadata.xml:
<metadata>
<groupId>acme</groupId>
<artifactId>acme</artifactId>
<version>1.0.0-SNAPSHOT</version>
<versioning />
</metadata>
If I'm interpreting the metadata files correctly (documentation online is scant), it appears machine B believes it has a newer version of the acme dependency (based on buildNumber) despite the fact that machine A last built it 6 days after machine B did (based on timestamp). Nexus also appears to be unaware of a universally correct buildNumber.
How could this situation possibly arise? What could I do to prevent my builds from failing due to inconsistent metadata? Have you experienced anything similar?
Important notes:
Both build machines have settings.xml files where the updatePolicy is "always".
Nexus does indeed have the newer version of acme that was built by A. B simply refuses to download it.
A and B are the only machines uploading to Nexus.
Both servers share the same system time.
All processes involved have write privileges to the metadata files so that they can be updated as necessary.
I was unable to find any open Maven or Nexus issues describing this behaviour.
Our CI server (Atlassian Bamboo) prevents builds of the same artifact from happening concurrently, so some race condition while uploading to Nexus is rather unlikely.
