Azure DevOps provides hosted agents as part of its build and release infrastructure. Hosted agents are virtual machines (VMs) that are managed by Microsoft and hosted in the Azure cloud. These agents can be used to run your CI/CD pipelines without the need to manage your own infrastructure. Here are key points to understand about Azure hosted agents:

1. Types of Hosted Agents:

   • Azure DevOps offers a variety of hosted agent pools, each optimized for specific scenarios and configurations. Some common types include:
     • Microsoft-hosted agents: These are general-purpose agents provided and maintained by Microsoft. They come with various pre-installed software stacks and tools.
     • Self-hosted agents: These agents run on your own infrastructure, which can be physical machines, virtual machines, or containers. You have full control over self-hosted agents and can customize their configurations.

2. Microsoft-Hosted Agents:

   • Microsoft provides a range of hosted agents with different configurations, including Windows, Linux, and macOS.
   • You can select the agent pool and agent specification that best matches your application’s requirements.

3. Agent Pools:

   • Hosted agents are organized into agent pools. Each agent pool can contain multiple agents with similar configurations.
   • You can choose which agent pool to use in your pipeline.

4. Agent Specifications:

   • Each agent within a pool has specific characteristics, such as the version of the operating system, tools, and software pre-installed.
   • You can select an agent specification that meets your build and deployment needs.

5. Availability and Scalability:

   • Microsoft-hosted agents are highly available and scalable. They automatically scale up and down based on the demand.
   • This ensures that your pipelines can run efficiently and without delays, even during high usage periods.

6. Pre-Installed Software:

   • Microsoft-hosted agents come with a wide range of pre-installed software, including popular programming languages, build tools, and deployment utilities.
   • You can further customize the environment by adding your own scripts and tools.

7. Agent Capabilities:

   • Each agent specification has a list of capabilities that specify which tools and software are available.
   • You can use these capabilities to select the appropriate agent for your pipeline jobs.

8. Licensing:

   • Licensing for software and tools on Microsoft-hosted agents is included in the cost of Azure DevOps services.

9. Self-Hosted Agents:

   • While Microsoft-hosted agents are convenient, you can also use self-hosted agents if you have specific requirements or need more control over the agent environment.
   • Self-hosted agents can be installed on your own infrastructure and connected to Azure DevOps.

10. Cost:

    • Microsoft-hosted agents have associated usage costs, and the cost varies depending on the agent pool and specification.
    • Usage is typically billed based on the amount of time your pipeline jobs run on these agents.

11. Integration with Pipelines:

    • You can easily specify which type of agent (Microsoft-hosted or self-hosted) to use in your pipeline YAML or through the Azure DevOps visual designer.

12. Agent Pools and Queues:

    • Azure DevOps uses agent pools and queues to manage agent assignments to jobs in pipelines.

13. Retention Policies:

    • Azure DevOps allows you to configure retention policies to control how long your pipeline runs and artifacts are kept on hosted agents.

Using Azure hosted agents in your CI/CD pipelines can significantly simplify your infrastructure management, reduce operational overhead, and provide a scalable and efficient build and deployment environment. You can select the appropriate agent specifications and pools to meet the needs of your applications and workloads.