Configuring Agent Demands in Azure DevOps

Configuring Agent Demands in Azure DevOps

In Azure DevOps, configuring Agent Demands allows you to specify certain requirements or constraints for the build or release agents that are used to run your pipelines. This helps ensure that the right agent is selected to run your tasks based on its capabilities.

Here are the steps to Configure Agent Demands.

1. Understanding Agent Demands

Agent Demands are conditions that you can apply to pipelines to control which agent is chosen for running jobs.

These demands can be based on:

• Agent capabilities: such as installed software, tools, or versions.

• Custom demands: that you define based on certain labels or environment variables.

2. Types of Demands

1. Predefined Demands: These are predefined by Azure DevOps based on agent capabilities. For example:

   • Agent.OS (the operating system of the agent, e.g., Windows, Linux)

   • Agent.Version (the version of the agent)

   • Agent.Name (the name of the agent pool)

   • Agent.MachineName (the machine name)

2. Custom Demands: These are custom requirements you can create for your specific needs, such as having a particular version of a tool or SDK installed.

3. Configure Agent Demands for a Pipeline:

To configure demands for an Azure DevOps pipeline, follow these steps:

A. Set Demands on a Pipeline Job (YAML-based pipelines):

In a YAML-based pipeline, you can configure demands using the demands keyword under the pool section.

Example YAML snippet:

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pool:
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  name: MyAgentPool
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  demands:
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   - agent.name -equals MySpecificAgent
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   - software.version -greaterThan 2.0
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   - Agent.OS -equals Windows_NT

This YAML configuration will ensure that the pipeline runs only on an agent that:

• Belongs to the pool MyAgentPool

• Has the name MySpecificAgent

• Has a software.version greater than 2.0

• Is running on a Windows_NT agent.

B. Set Demands on a Classic Build Pipeline (UI-based pipelines):

1. Go to Pipelines > Builds in the Azure DevOps portal.

2. Select the pipeline you want to configure.

3. Click on the Edit button to modify the pipeline.

4. In the pipeline, click on the Agent Pool section (this may be in the "Job" section of the pipeline configuration).

5. Select the Agent Pool you want to use.

6. Under the Demands section, click + Add Demand.

7. You can now configure the demand by selecting the Capability (e.g., Agent.OS, Agent.Name, etc.) and the corresponding operator and value.

Example:

• Capability: Agent.OS

• Operator: Equals

• Value: Windows_NT

You can add multiple demands for more complex requirements.

C. Using Agent Capabilities (UI-based configuration):

Agent pools in Azure DevOps have capabilities that are automatically discovered when agents are installed. These capabilities include things like:

• Installed software versions

• Specific tools (e.g., Java, Node.js)

• Environment variables

When you configure demands, you can reference these capabilities to ensure that the pipeline runs only on agents that meet specific criteria.

4. Creating and Using Custom Capabilities

If you need custom software or configurations that aren't part of the default capabilities, you can configure custom capabilities on agents.

• Navigate to Project settings > Agent pools.

• Select the agent pool where your agent resides.

• Click on the specific agent and then Manage capabilities.

• You can add custom capabilities (for example, a specific SDK version or custom environment variables) here.

Then, in your pipeline, you can use these custom capabilities as demands.

5. Examples of Common Demands

Demanding a specific version of a tool:

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demands:
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   - java.version -equals 11

Demanding a particular OS:

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demands:
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   - Agent.OS -equals Windows_NT

Demanding a specific version of an agent:

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demands:
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   - Agent.Version -equals 2.179.0

Demanding a custom capability:

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demands:
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   - my.custom.capability -equals true

Best Practices

1. Minimize demands: Only set demands that are truly required. Overly restrictive demands can make it harder for your pipeline to find an available agent.

2. Use agent pools effectively: Group agents by their capabilities and target specific pools based on your build or release requirements.

3. Monitor agent availability: Ensure that agents in your pool are frequently available and capable of handling the workload your demands impose.

Summary

By configuring agent demands in Azure DevOps, you can ensure that your builds and releases run only on suitable agents with the required tools, operating systems, and configurations.