Azure WebApp Deployment task not recognizing variable - azure-devops

Question

When running the following task in a pipeline
- task: AzureRmWebAppDeployment#3
displayName: 'Azure App Service Deploy: Web App'
inputs:
azureSubscription: ${{ parameters.azureSubscription }}
WebAppName: $[dependencies.preDeploy.outputs['webAppName']]
Package: '$(Pipeline.Workspace)/**/PackageTmp'
WebAppUri: WebAppUrl
UseWebDeploy: true
AdditionalArguments: '-useChecksum'
RenameFilesFlag: true
enableXmlVariableSubstitution: true
it complains about the variable I am assigning to the WebAppName
##[error]Error: Failed to get resource ID for resource type 'Microsoft.Web/Sites' and resource name '$[dependencies.preDeploy.outputs['webAppName']]'. Error: {"error":{"code":"InvalidFilterInQueryString","message":"Invalid $filter 'resourceType EQ 'Microsoft.Web/Sites' AND name EQ '$[dependencies.preDeploy.outputs['webAppName']]'' specified in the query string."}} (CODE: 400)
Why is the variable not being replaced with its actual value?

Answer 1

Your variable needs to be addressed by its reference name, which is usually the step name the variable came from.
If you want to make a variable available to future jobs, you must mark it as an output variable using isOutput=true. Then you can map it into future jobs using $[] syntax and including the step name which set the variable.
More reading about Multi-job Variables
See myVarFromJobA: $[ dependencies.A.outputs['setvarStep.myOutputVar'] ]
in the below example.
jobs:
# Set an output variable from job A
- job: A
pool:
vmImage: 'vs2017-win2016'
steps:
- powershell: echo "##vso[task.setvariable variable=myOutputVar;isOutput=true]this is the value"
name: setvarStep
- script: echo $(setvarStep.myOutputVar)
name: echovar
# Map the variable into job B
- job: B
dependsOn: A
pool:
vmImage: 'ubuntu-16.04'
variables:
myVarFromJobA: $[ dependencies.A.outputs['setvarStep.myOutputVar'] ] # map in the variable
# remember, expressions require single quotes
steps:
- script: echo $(myVarFromJobA)
name: echovar