TFS rest API - queue build on same machine - tfs

Question

I am trying to see if it is possible to queue a build on the same VM as another build. Note, I am in the vNext system. I know it is possible to configuration information about the agent queues. but I want to get a little more specific than that. I'm not sure if what I want falls outside of build best practices, but I'd like to ask anyway.
Consider the following setup for builds A & B:
There are 4 agents: 2 on server 1, 2 on server 2 Any agent can pick up build A or build B .... I know how to set up the demands so only agents on those VMs can pick up this builds.
Build A uses the rest API to queue build B, and wait for it to complete. Right now, under current configurations, the spawned build B can be picked up by any of the 3 remaining agents on (so the free agent on the same machine as build A, or any of the agents on the other server).
I want to try to run build B on the same server as build A when build A launches build B. In other words, if an agent on server 1 picks up build A, I want the build B it launches to use the same server (using the other agent on the machine). Conversely, if the server 2 picks up build A, I want the build B it launches to be picked up by server 2 as well. Assuming I know things like the Agent ID, Agemt Machine Name, etc, I wanted to use the rest API in c# to simulating launching build B to try to control which machine picks it up.
I could configure agents so that both builds only run on 1 machine, but I am trying to avoid running too many agents on one machine. I could configure the above 4 agents to run on 1 machine, but I want to distribute the agents as much as possible. I know it is possible to specify information about agents queues / pools etc, bot not the machine. I am trying to avoid having to restrict the number of machines that run a set of agents.
I know this may seem a bit unusual ... but I am dealing with a scenario where I want to share information between the builds that will be simplified if they run on the same machine. If build B is launched by itself, it doesn't matter what machine picks it up. If this isn't possible, I will try other ways to share information between the builds.
Is it possible to do this?

Answer 1

Yes, you can achieve that by set up the demands with REST API when queue the build.
For example, you can use below PowerShell script to queue a build with the specific agent:
Param(
[string]$collectionurl = "http://server:8080/tfs/DefaultCollection/",
[string]$projectName = "ProjectName",
[string]$keepForever = "true",
[string]$BuildDefinitionId = "1",
[string]$user = "username",
[string]$token = "password"
)
# Base64-encodes the Personal Access Token (PAT) appropriately
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $user,$token)))
function CreateJsonBody
{
$value = #"
{
"definition": {
"id": $BuildDefinitionId
},
"sourceBranch": "$/xxxx",
"demands":["Agent.Name -equals Agent1"]
}
}
"#
return $value
}
$json = CreateJsonBody
$uri = "$($collectionurl)/$($projectName)/_apis/build/builds?api-version=2.0"
$result = Invoke-RestMethod -Uri $uri -Method Post -Body $json -ContentType "application/json" -Headers #{Authorization=("Basic {0}" -f $base64AuthInfo)}
In your scenario: (Assume that Agent1 is the name of the agent, you can get it from Agent Capabilities)
Server1 : Agent1, Agent2
Server2 : Agent3, Agent4
If Build A queued with Agent1, then you an set "demands":["Agent.Name -equals Agent2"] to queue Build B.
Same thing, if Build A queued with Agent3, then you an set "demands":["Agent.Name -equals Agent4"] to queue Build B.
You can also create a simple PowerShell script and add a PowerShell step as the end of the build step in definition A, then run the PS script to queue build B once Build A completed.
If you want to queue build with the REST API in C#, then you can reference below thread:
Queue vNext build from c# using REST API (Tfs on premise)