In Azure DevOps, the term “VM Image” usually refers to the pre-configured virtual machine images used in Azure Pipelines for running your builds and deployments. These VM images are part of Microsoft-hosted agents, which provide the environment where your pipeline runs. Here’s some key information about using VM images in Azure DevOps:

Understanding Microsoft-hosted Agents and VM Images

1. Microsoft-hosted Agents:

   • These agents are provided by Azure DevOps and are automatically updated and maintained by Microsoft.
   • Each time a pipeline runs, a fresh instance of the VM image is provisioned.

2. VM Images:

   • VM Images are predefined with specific operating systems and are equipped with a set of tools and software required for the CI/CD process.
   • Common images include Ubuntu, Windows, and macOS.

Common VM Images in Azure DevOps

• Ubuntu: Used for Linux-based builds and deployments.
• Windows: Includes various versions like Windows Server 2019, and others, for Windows-based pipelines.
• macOS: For building and deploying on Apple’s operating system, especially useful for iOS or macOS applications.

Specifying VM Images in Your Pipeline

In your Azure DevOps pipeline (YAML), you specify the VM image using the vmImage keyword under pool. Here is an example of how to specify different VM images:

Customizing Environments

While Microsoft-hosted agents with pre-defined VM images provide convenience, sometimes you may need a more customized environment:

• Self-hosted Agents: If the predefined VM images don’t meet your requirements, you can set up self-hosted agents. These are VMs or physical machines that you set up and configure for your specific needs.

• Container Jobs: You can run your jobs inside a container, which allows you to define your own runtime environment with the specific tools and versions you need.

Considerations

• Preinstalled Software: Microsoft-hosted agents come with a lot of preinstalled software, but the versions may not always align with your requirements. Check Microsoft’s documentation for the current list of preinstalled software.

• Limitations: Microsoft-hosted agents have some limitations in terms of run duration and compute resources. For long-running jobs or jobs that require more resources, consider self-hosted agents.

• Updates: Microsoft regularly updates these images, so it’s essential to be aware of changes that might affect your pipelines.

By choosing the right VM image for your Azure DevOps pipelines, you ensure that your CI/CD processes run smoothly and efficiently on the appropriate platform.