Skip infrastructure deployments if there are no changes to deploy (Azure Pipelines)

_Readme.md

Skip infrastructure deployments if there are no changes to deploy (Azure Pipelines)

One devops strategy is to keep infrastructure state and code in a single repository, and deploy them together. It ensures your infrastructure is always in the correct state to match the version of your code.

The downside is that infrastructure deployments are slow, and generally don't change as frequently as code.

This gist shows how to skip an infrastructure deployment task if there are no changes in a particular sub-path of the repository.

It takes advantage of the pipelines API, which can provide a list of all commits since the last successful pipeline execution. This ensures that it works even when multiple commits are pushed at once, or when the build with the infrastructure change failed. The pipelines API does the hard work of working out which commits need checking.

azure-pipelines.yaml

resources:
  repositories:
    - repository: self
      type: git
      ref: main

stages:
  - stage: Build
    pool:
      vmImage: ubuntu-latest
    jobs:
      - job: BuildJob
        displayName: Build Job
        steps:
          - checkout: self
            clean: true
          - task: PowerShell@2
            inputs:
              filePath: "azure-pipelines/Test-ChangesMadeInPath.ps1"
              arguments: >-
                -authorisation "Bearer $(system.accesstoken)" 
                -pathFilter "azure-pipelines/deployment" 
                -buildId $(Build.BuildId)'
                -collectionUri $(System.CollectionUri)
                -project $(System.TeamProject)
            name: DetermineChangesMadeInDeploymentFolder
            env:
              SYSTEM_ACCESSTOKEN: $(system.accesstoken)
          - task: DotNetCoreCLI@2
            displayName: Build project
            inputs:
              projects: "**/*.csproj"
              arguments: --output publish_output --configuration Release
          - task: PublishBuildArtifacts@1
            displayName: "Publish Artifact: drop"

  - stage: Deploy
    pool:
      vmImage: ubuntu-latest
    condition: and(succeeded(), eq(variables['build.sourceBranch'], 'refs/heads/main'))
    jobs:
      - deployment: DeployInfrastructure
        condition: eq(stageDependencies.Build.BuildJob.outputs['DetermineChangesMadeInDeploymentFolder.filesUpdated'], 'True')
        displayName: Deploy infrastructure
        environment: "prod"
        strategy:
          runOnce:
            deploy:
              steps:
                - template: deployment/YAML/deploy-infrastructure.yml
                  parameters:
                    environment: $(Environment.Name)
      - deployment: DeployCode
        displayName: Deploy code
        dependsOn: DeployInfrastructure
        condition: in(dependencies.DeployInfrastructure.result, 'Succeeded', 'Skipped')
        environment: "prod"
        strategy:
          runOnce:
            deploy:
              steps:
                - template: deployment/YAML/deploy-code.yml
                  parameters:
                    environment: $(Environment.Name)

Test-ChangesMadeInPath.ps1

[CmdletBinding()]
param (
  $authorisation,
  $pathFilter,
  $collectionUri,
  $project,
  $buildId
)

$changesUrl = "$collectionUri/$project/_apis/build/builds/$buildId/changes?api-version=6.0"
$changesResponse = Invoke-RestMethod -Uri $changesUrl -Headers @{Authorization = $authorisation } -Method Get
$commits = @($changesResponse.value | ForEach-Object { $_.id })

Write-Host "##vso[task.setvariable variable=filesUpdated;isOutput=true]False"
Write-Host "Checking $($commits.Length) commits for changes matching path $pathFilter"
for ($j = 0; $j -lt $commits.Length; $j++) {
  Write-Host "Checking commit: $($commits[$j]) with its parent"
  $files = $(git diff "$($commits[$j])~" $commits[$j] --name-only)
  Write-Host $files
  if ($files -like "*$pathFilter/*") {
    Write-Host "Found file matching path filter in commit $($commits[$j])"
    Write-Host "##vso[task.setvariable variable=filesUpdated;isOutput=true]True"
    break
  }
}