Different agent pool or demands for the same Azure Pipeline based on trigger - azure-devops

Question

I have an Azure Pipeline written in YAML which runs from a CI trigger whenever changes are made to the master branch. It can also be manually triggered from Pull Requests or by users against any branch.
Due to the use of a number of licensed components, the build from master needs to run on a specific agent. The other builds do not, and in fact I would rather they run on other agent(s).
So my question is, is there any way to specify a different agent/pool within the YAML pipeline based on what triggered the build, or what branch the build is building? I'd like this to be behaviour which is configured in the pipeline permanently, rather than requiring users to update the YAML on each branch they wish to build elsewhere.
I can't see anything obvious in the sections of the documentation on the pool/demands/condition keywords.

Answer 1

I solved this by putting the steps for the job into a template, and then creating a set of jobs in the pipeline with different condition entries, so that we can set demands based on those conditions.
A skeleton version looks like this:
- stage: Build
jobs:
- job: TopicBranchAndPullRequestBuild
condition: or(startsWith(variables['Build.SourceBranch'], 'refs/heads/topic'), startsWith(variables['Build.SourceBranch'], 'refs/pull'))
displayName: 'Build topic Branch or Pull Request'
pool:
name: the-one-and-only-pool
demands:
- HasLicensedComponents -equals false
steps:
- template: build-template.yml
- job: MasterAndReleaseBranchBuild
condition: or(eq(variables['Build.SourceBranch'], 'refs/heads/master'), startsWith(variables['Build.SourceBranch'], 'refs/heads/release'))
displayName: 'Build master or release Branch'
pool:
name: the-one-and-only-pool
demands:
- HasLicensedComponents -equals true
steps:
- template: build-template.yml
Obviously the values given here are for example only, but otherwise this is what I have working.

Answer 2

Could you try expressions? I've used this with success on variable groups so it might work on agent pools.
- ${{ if eq(variables['build.SourceBranchName'], 'prod') }}:
- pool: Host1
- ${{ if eq(variables['build.SourceBranchName'], 'staging') }}:
- pool: Host2
- ${{ if not(and(eq(variables['build.SourceBranchName'], 'staging'), eq(variables['build.SourceBranchName'], 'prod'))) }}:
- pool: Host3
Credit for original workaround for dynamically pulling variable groups here: https://github.com/MicrosoftDocs/vsts-docs/issues/3702#issuecomment-574278829

Answer 3

The pool keyword specifies which pool to use for a job of the pipeline. A pool specification also holds information about the job's strategy for running. You can specify a pool at the pipeline, stage, or job level. The pool specified at the lowest level of the hierarchy is used to run the job.
is there any way to specify a different agent/pool within the YAML
pipeline based on what triggered the build, or what branch the build
is building?
For this issue , you can create different yaml files for different branches, specify different agent pools in the corresponding yaml file.
You can switch to the yaml file of different branches in pipeline with the option shown below:

Answer 4

parameters:
- name: self_hosted_agent
displayName: Choose your pool agent
type: string
default: windows-latest
values:
- windows-latest
- self-hosted
- name: agent_name
displayName: Choose your agent
type: string
default: 'Laptop Clint'
values:
- 'Laptop Clint'
- 'Laptop Eastwood'
variables:
- name: pool_agent_key
${{ if eq(parameters.self_hosted_agent, 'windows-latest') }}:
value: vmImage
${{ if eq(parameters.self_hosted_agent, 'self-hosted') }}:
value: name
- name: pool_agent_value
${{ if eq(parameters.self_hosted_agent, 'windows-latest') }}:
value: windows-latest
${{ if eq(parameters.self_hosted_agent, 'self-hosted') }}:
value: Iot-Windows
- name: agent_name
value: ${{ parameters.agent_name }}
stages:
- stage: build
displayName: Build
pool:
${{ variables.pool_agent_key }}: ${{ variables.pool_agent_value }}
${{ if eq(parameters.self_hosted_agent, 'self-hosted') }}:
demands:
- agent.name -equals ${{ variables.agent_name }}