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Azure DevOps pipelines use YAML to define build and release workflows in a human- and machine-readable format. In this guide, we’ll explore YAML essentials, step through an ASP.NET pipeline example, and demonstrate how to leverage templates for reusable CI/CD components.
YAML is both concise and clear, making it ideal for version-controlled CI/CD definitions. Learn more at the YAML Official Site.

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Example: ASP.NET CI/CD Pipeline

Use the following ASP.NET pipeline to build, test, and package your web application. For full task details, see the Azure DevOps ASP.NET docs. 
trigger:
  - master

pool:
  vmImage: 'windows-latest'
  name: 'Default'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'

steps:
  - task: NuGetToolInstaller@1

  - task: NuGetCommand@2
    inputs:
      restoreSolution: '$(solution)'

  - task: VSBuild@1
    inputs:
      solution: '$(solution)'
      msbuildArgs: >-
        /p:DeployOnBuild=true
        /p:WebPublishMethod=Package
        /p:PackageAsSingleFile=true
        /p:SkipInvalidConfigurations=true
        /p:PackageLocation="$(build.artifactStagingDirectory)\$(Build.BuildId).zip"
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'

  - task: VSTest@2
    inputs:
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'

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Starter Pipeline

Begin with a minimal YAML pipeline and customize it for your project: 
trigger:
  - master

pool:
  vmImage: 'ubuntu-latest'
  name: 'Default'

steps:
  - script: echo Hello, world!
    displayName: 'Run a one-line script'

  - script: |
      echo Add other tasks to build, test, and deploy your project.
      echo See https://aka.ms/yaml
    displayName: 'Run a multi-line script'
Key elements:
  • trigger: Events that kick off the pipeline.
  • pool: Agent selection (e.g., ubuntu-latest).
  • steps: Tasks or scripts to execute in sequence.

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Viewing a Pipeline Run

A typical Azure DevOps pipeline run reveals build warnings, repository info, branch, and elapsed time:
The image shows an Azure DevOps pipeline run summary with warnings related to possible null reference dereferences in the code. It includes details like the repository, branch, and time elapsed.

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Creating a New Pipeline

When you create a pipeline, select your source—Azure Repos Git, Bitbucket Cloud, GitHub, or GitHub Enterprise—and choose the Starter Pipeline for IntelliSense support:
The image shows an Azure DevOps interface for creating a new pipeline, with options to select the code source from Azure Repos, Bitbucket Cloud, GitHub, or GitHub Enterprise Server.
The default YAML appears: 
trigger:
  - master

pool:
  vmImage: 'ubuntu-latest'
  name: 'Default'

steps:
  - script: echo Hello, world!
    displayName: 'Run a one-line script'
  - script: |
      echo Add other tasks to build, test, and deploy your project.
      echo See https://aka.ms/yaml
    displayName: 'Run a multi-line script'
Validate and run to see output: 
Starting: Run a one-line script
> echo Hello, world!
  Hello, world!

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YAML Structure Basics

YAML relies on three core constructs: key–value pairs, lists, and nested mappings. Use indentation for hierarchy and avoid tabs.
Syntax TypeDescriptionExample
Key–value pairMaps a key to a single valuetrigger: [master]
ListDefines an ordered sequencefruits: [Apple, Banana, Cherry]
Nested mappingEmbeds mappings under a parent keypool:\n vmImage: ubuntu-latest\n name: Default
Examples: Key–value pair: 
trigger:
  - master
List: 
fruits:
  - Apple
  - Banana
  - Cherry
Nested mapping: 
pool:
  vmImage: ubuntu-latest
  name: Default

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Variables and Overrides

Define pipeline variables at the top and allow runtime overrides: 
variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'
  pipelineRunnerName: 'DefaultUser'
  pipelineRunnerAge: 30

steps:
  - script: echo Hello, $(pipelineRunnerName)!
    displayName: 'Greet runner'
  - script: echo Runner age is $(pipelineRunnerAge)
    displayName: 'Show runner age'
Users can override pipelineRunnerName and pipelineRunnerAge on the Run Pipeline screen. Ensure correct defaults to avoid unexpected behavior.

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Best Practices

  • Leverage comments to clarify intent.
  • Keep pipelines DRY by defining reusable variables and templates.
  • Organize common logic into separate files.

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Applying Templates

Break out common steps into parameterized or extendable templates. Example templates: nuget.yml 
steps:
  - task: NuGetToolInstaller@1
  - task: NuGetCommand@2
    inputs:
      command: 'restore'
      restoreSolution: '$(solution)'
build.yml 
steps:
  - task: VSBuild@1
    inputs:
      solution: '$(solution)'
      msbuildArgs: >-
        /p:DeployOnBuild=true
        /p:WebPublishMethod=Package
        /p:PackageAsSingleFile=true
        /p:SkipInvalidConfigurations=true
        /p:PackageLocation="$(build.artifactStagingDirectory)"
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'
test.yml 
steps:
  - task: VSTest@2
    inputs:
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'
Reference templates in your main pipeline (azure-pipelines.yml): 
trigger:
  - master

pool:
  vmImage: 'ubuntu-latest'
  name: 'Default'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'
  pipelineRunnerName: 'DefaultUser'
  pipelineRunnerAge: 30

steps:
  - script: echo Hello, $(pipelineRunnerName)!
    displayName: 'Greet runner'

  - template: 'nuget.yml'
  - template: 'build.yml'
  - template: 'test.yml'

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Build and Test Summaries

After applying templates, review your build results in the pipeline summary:
The image shows an Azure DevOps pipeline run summary with details about a specific build, including warnings related to null reference dereferencing. The build is triggered by a user and shows test results and code coverage.
Monitor recent runs and their status:
The image shows an Azure DevOps pipeline interface with a list of recent pipeline runs for "KodeKloudData," each marked with a green check indicating successful completion.
Check detailed logs to confirm test success:
The image shows an Azure DevOps pipeline run with a list of completed jobs, all marked as successful, and a log indicating that 100% of tests passed.

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Conclusion

Azure DevOps YAML templates enable modular, maintainable CI/CD pipelines. You’ve learned:
  • Core YAML syntax and structure
  • Defining variables and overrides
  • Extracting and reusing templates
  • Reviewing build and test outcomes
Experiment with these patterns to streamline your Azure DevOps workflows.

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