Variable from expression in YAML Pipeline with dynamic variable group - azure-devops

Question

I am trying to assign value of the variable by coalescing (via expression) from parameter and variable that is in variable group.
Problem is, that the variable group is dynamic, depending on another parameter (like DEV, QA,...)
Pipeline can't see the value of the variable ResourceGroupName which comes from variable group MyAPIVarGroup-*. It comes empty.
Is this even achievable and I'm just doing something wrong? Or is this not possible with the current implementation of expressions and variable groups in YAML pipelines?
# Parameter of the target environment to deploy to
- name: targetEnvironmentParam
displayName: Target environment of the deployment
type: string
default: 'DEV'
values:
- DEV
- QA
# Parameter of the custom resource group suffix (suffix not used later if not filled)
- name: resGroupOverrideParam
displayName: "[OPTIONAL] Custom resource group name"
type: string
default: ' '
variables:
# Variable group to be used (based on environment)
- ${{ if eq(parameters.targetEnvironmentParam, 'DEV') }}:
- group: MyAPIVarGroup-DEV
- ${{ if eq(parameters.targetEnvironmentParam, 'QA') }}:
- group: MyAPIVarGroup-QA
- name: resGroupName
value: ${{ coalesce(parameters.resGroupOverrideParam, variables.ResourceGroupName, 'default is wrong') }}

Answer 1

So, what you are experiencing is the fact that ${{ }} expressions are evaluated before the pipeline is run so the variable from the variable group is empty at compile time (not known). See this article for more details on expressions and evaluation:
https://learn.microsoft.com/en-us/azure/devops/pipelines/process/expressions?view=azure-devops
There are also runtime expressions that you could use instead but they do not allow access to pipeline parameters so you would need to assign the override value to a variable for use in evaluating the coalesce() statement like this (note the replace function to trim the default value of the override parameter to an empty string):
parameters:
- name: targetEnvironmentParam
displayName: Target environment of the deployment
type: string
default: 'DEV'
values:
- DEV
- QA
- name: resGroupOverrideParam
displayName: "[OPTIONAL] Custom resource group name"
type: string
default: ' '
variables:
- ${{ if eq(parameters.targetEnvironmentParam, 'DEV') }}:
- group: MyAPIVarGroup-DEV
- ${{ if eq(parameters.targetEnvironmentParam, 'QA') }}:
- group: MyAPIVarGroup-QA
- name: resGroupOverride
value: ${{ replace(parameters.resGroupOverrideParam, ' ', '') }}
- name: resGroupName
value: $[ coalesce(variables['resGroupOverride'], variables.ResourceGroupName, 'default is wrong') ]
steps:
- pwsh: |
Write-Host $(resGroupName)
You could also stick with just compile time expressions with the following example instead which relies on overriding the same variable name from a group if the optional parameter is set with something other than a space:
parameters:
- name: targetEnvironmentParam
displayName: Target environment of the deployment
type: string
default: 'DEV'
values:
- DEV
- QA
- name: resGroupOverrideParam
displayName: "[OPTIONAL] Custom resource group name"
type: string
default: ' '
variables:
- group: MyAPIVarGroup-${{ parameters.targetEnvironmentParam }}
- ${{ if ne(parameters['resGroupOverrideParam'], ' ') }}:
- name: resGroupName
value: ${{ parameters.resGroupOverrideParam }}
steps:
- pwsh: |
Write-Host $(resGroupName)
This example pipeline always loads a variable group and both groups have a variable named the same thing. Also, if the override parameter is set then the pipeline itself will create a variable and set the value to the parameter which because it is declared after the variable group will override that value.