Friday, 20 June 2008

MSBuild RE: Enforcing the Build Agent in a Team Build

This is a post that responds to a post by Michael Ruminer at Enforcing the Build Agent in a Team Build. I hope I correctly understand his situation. Here is my summary of it.

You have a specified value for the property BuildAgentName
You create various MSBuild scripts that will hook into a TeamBuild
You want to specify in each MSBuild script the names of the build agents that are allowed to run the build
If the current value for BuildAgentName is not in the list above, fail the build otherwise allow it to continue

My solution to this problem is to create a property, AllowedBuildAgents, which will contain a semi-colon separated list of the allowed build agent names. Then this is converted into an item, AllowedBuildAgentsItem, so batching can be preformed over it. If you are not familiar with MSBuild batching you can see my previous postings at:

The main objective here is to create an item that contains all the allowed names, AllowedBuildAgentsItem, and batch over them. If the value for BuildAgentName is equal to any value in that item then we want to allow the build. I create a property BuildAgentAllowed which defaults to false, and if that condition is true then I set BuildAgentAllowed to true. So I created a target DetermineIfAuthorizedBuildAgent that depends will throw an error if BuildAgentAllowed is false. Also this target depends on the target that will actually populate that value, which is the GetBuildAgentAllowed target. The build script is placed below. I added a few elements that were for demo only. Those are; value for BuildAgentName and BeforeEndToEndIteration target. See comments in the file (which can be downloaded at the end of this post).

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="2.0"
         xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
         DefaultTargets="BeforeEndToEndIteration">


<PropertyGroup>
    <BuildAgentName>Sayed_001</BuildAgentName>
</PropertyGroup>

<PropertyGroup>
    <BeforeEndToEndIterationDependsOn>
      $(BeforeEndToEndIterationDependsOn);
      DetermineIfAuthorizedBuildAgent;
    </BeforeEndToEndIterationDependsOn>
</PropertyGroup>


<PropertyGroup>
    <AllowedBuildAgents>Sayed_001;Sayed_003;Sayed_005</AllowedBuildAgents>
</PropertyGroup>


<ItemGroup>
    <AllowedBuildAgentsItem Include="$(AllowedBuildAgents)"/>
</ItemGroup>

<PropertyGroup>
    <BuildAgentAllowed>false</BuildAgentAllowed>
</PropertyGroup>

<Target Name="PrintInfo">
    <Message Text="AllowedBuildAgentsItem: @(AllowedBuildAgentsItem,'%0a%0d')"/>
</Target>


<Target Name="DetermineIfAuthorizedBuildAgent"
          DependsOnTargets="GetBuildAgentAllowed">
    <Message Text="BuildAgentAllowed: $(BuildAgentAllowed)"/>
    <Error Text="This build can only be run on one of the following build agents: @(AllowedBuildAgentsItem)"
           Condition="'$(BuildAgentAllowed)'=='false'" />
</Target>


<Target Name="GetBuildAgentAllowed" Outputs="%(AllowedBuildAgentsItem.Identity)">
    <Message Text="GetBuildAgentAllowed %25(AllowedBuildAgentsItem.Identity): %(AllowedBuildAgentsItem.Identity)"/>

    <CreateProperty Value="true" Condition="'$(BuildAgentName)'=='%(AllowedBuildAgentsItem.Identity)'">
      <Output PropertyName="BuildAgentAllowed" TaskParameter="Value"/>
    </CreateProperty>

</Target>


<Target Name="BeforeEndToEndIteration" DependsOnTargets="$(BeforeEndToEndIterationDependsOn)">
    <Message Text="EndToEndIteration starting"/>
</Target>

</Project>

The only reason that I have defined the allowed build agents in a property (AllowedBuildAgents) is because I want to allow external sources to specify it. You can specify properties through the command line or when using the MSBuild Task. Then the script converts this to an item. If I execute this project I would expect it to succeed because the defined value for BuildAgentName is contained in the list of AllowedBuildAgents. The results of executing this project are shown below.

Now we can change the value for BuildAgentName, by using the command msbuild.exe BuildAgent01.proj /p:BuildAgentName=Sayed_010. We would expect the build to fail. The results of this are below.