How to add a new dynamically discoverable capability to an agent? - azure-devops

Question

Updates
I am going to propose a Capabilities Provider here as an update to my post.
If you need more details please let me know.
We currently have a bunch of shipped Capabilities Providers in the agent source code:
https://github.com/microsoft/azure-pipelines-agent/tree/master/src/Microsoft.VisualStudio.Services.Agent/Capabilities
Agent
Environment
Nix
PowerShell
What is being proposed is one additional Provider named ExecutableCapabilitiesProvider.
This new ExecutableCapabilitiesProvider will probably have a config file which can be edited on the agent machine.
The format of this file could probably be:
#name,executable
pip,pip3 freeze
xyz,/usr/bin/xyz-runner
abc,sh -C "ls -l /blah/blah"
As the maintainer of the self-hosted pool, I would configure this file with entries suiting me and have the agent run it as it starts. This way I am not hard-coding any values for my capabilities but rather those be determined at the start up.
And I would go one step further and add a new API call to add capabilities which is more flexible than the current one asking for name/values. An example, would be to change the parameters to Name, Provider, Params:
efg, NixProvider, /path/to/file/efg
klm, ExecutableCapabilitiesProvider, /usr/bin/klm -a -b -c
Original Post
I'd like to make my agents report on new capabilities which are not static but rather result of a command or something similar? How can I do that?
Our agents run on linux boxes.
To be specific, I'd like to have a new capability called pip-packages and the value for that is the result of the command pip freeze executed on the shell.

Answer 1

If you mean to add User-defined capabilities, then you can write a script to call the REST API to update the agent capabilities.
PUT https://dev.azure.com/{organization}/_apis/distributedtask/pools/{poolid}/agents/{agentid}/usercapabilities?api-version=5.0
Request body:
{"pip-packages": "xxxx"}
For example, you can set a variable and run command pip freeze and export the response as the value of that variable, then update the agent capability by calling the REST API:
Below PowerShell sample for your reference :
Param(
[string]$collectionurl = "https://dev.azure.com/{organization}",
[string]$poolid = "14",
[string]$agentid = "16",
[string]$user = "user",
[string]$token = "PAT/Password"
)
# Base64-encodes the Personal Access Token (PAT) appropriately
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $user,$token)))
# Run pip freeze command and get response as the value of the variable $pipfreeze (Just for your reference here, you need to extract the value with running the commands)
$pipfreeze = "response of pip freeze"
# Create json body with that value
$baseUri = "$collectionurl/_apis/distributedtask/pools/$poolid/agents/$agentid/usercapabilities?api-version=5.0"
function CreateJsonBody
{
$value = #"
{"pip-packages":"$pipfreeze"}
"#
return $value
}
$json = CreateJsonBody
# Update the Agent user capability
$agentcapability = Invoke-RestMethod -Uri $baseUri -Method Put -Body $json -ContentType "application/json" -Headers #{Authorization=("Basic {0}" -f $base64AuthInfo)}
write-host "=========================================================="
Write-host "userCapabilities :" $agentcapability.userCapabilities.'pip-packages'
write-host "=========================================================="