Designing an Agent Infrastructure

In this article, we’ll explore how to design and configure build agent infrastructure in Azure DevOps. You’ll learn the differences between hosted and self-hosted agents, see how to launch agents on Windows, Linux, Docker, and macOS, and review best practices for scaling and customization.

Hosted vs. Self-Hosted Agents

Build agents in Azure Pipelines fall into two categories:

Host agents are turnkey and zero-maintenance, while self-hosted agents give you full control over the software stack and cost structure.

Viewing Agent Pools

Navigate in Azure DevOps to Organization settings → Agent pools to see all your pools and agents:

Here you’ll find pools like Azure Pipelines (hosted), Default, Linux, and Mac.

Hosted Agents

The Azure Pipelines pool contains Microsoft-hosted agents:

• Always online and listening
• Supports Windows, Linux, and macOS jobs
• No infrastructure maintenance required

Setting Up Self-Hosted Agents

Self-hosted agents run on machines you control—physical servers, cloud VMs, or containers. Below are step-by-step examples for Windows, Docker, Linux (WSL & standalone), and macOS.

1. Windows Self-Hosted Agent

In the Default pool, you might see two offline Windows agents:

To bring one online:

# Change into your agent folder
cd C:\agent

# Run the agent service
.\run.cmd

Sample output:

Scanning for tool capabilities.
Connecting to the server.
2024-09-26 17:57:45Z: Listening for Jobs

The agent is now online and ready to accept jobs.

2. Docker-Based Agent

Containerize your agent for easier scaling and reproducibility:

REM File: start.bat in your project’s azpbuild folder
docker run `
  -e AZP_URL="%AZP_URL%" `
  -e AZP_TOKEN="%AZP_TOKEN%" `
  -e AZP_POOL="Default" `
  -e AZP_AGENT_NAME="Docker Agent - Windows" `
  --name azp-agent-windows `
  azp:agent

Run it:

cd C:\Projects\agents\azpbuild
start.bat

Now both your native Windows agent and the containerized agent will appear online.

3. Linux Agents

In the Linux pool you may have agents for WSL or standalone servers:

WSL Agent

On Windows with WSL installed:

cd ~/myagent
./run.sh

You’ll see:

Scanning for tool capabilities.
Connecting to the server.
2024-09-26 17:57:45Z: Listening for Jobs

Standalone Linux Server

On a dedicated Linux VM (e.g., Arch, Ubuntu):

cd ~/myagent
./run.sh

Output is identical—just toggle the agent on or off as needed.

4. macOS Agent

SSH into your Mac build host and start the agent:

ssh jeremy@Jeremys-Mac-Studio
cd ~/myagent
./run.sh

Scanning for tool capabilities.
Connecting to the server.
2024-09-26 17:57:45Z: Listening for Jobs

The macOS agent will show up under the Mac pool.

Choosing the Right Infrastructure

When architecting your agent setup, evaluate:

• Target OS: Windows, Linux, macOS
• Management overhead: Hosted zero-touch vs. self-hosted control
• Customization needs: Specific SDKs, Docker images, hardware
• Scaling strategy: Manual scaling, Kubernetes, or VM auto-scaling

Containerized, self-hosted agents strike a strong balance for most teams—offering full customization with industry-standard orchestration tools like Kubernetes.

Links and References

• Azure DevOps Services
• Azure Pipelines
• Docker Official Site
• Kubernetes Documentation