Azure DevOps agents ...

August 15, 2023

In the previous articles, we learned that the Azure DevOps pipelines can be used to build and deploy

A job is a building block of a pipeline and is a collection of steps

To run a job, we require some infrastructure and the infrastructure is called the agent

In this article, we will learn about the agent

Azure DevOps Agent:

To build or release an application we will need at least one agent. Based on the scale of the project, we might need more agents

when a pipeline is executed, a job will begin to run in the agent

Azure DevOps Agent types:

Based on the ownership of the agent infrastructure, there are two major categories of Azure DevOps agents

  • Microsoft-hosted agents
  • Self-hosted agents

Microsoft hosted agent:

Microsoft provides agents with a predefined set of tools, upgrades and maintenance of these agents are taken care of by Microsoft

whenever we try to run a pipeline, behind the scenes - a fresh virtual machine will be created and allocated to run a job and discarded after a job completion

This also means that the changes done on the VM filesystem by the job will not be persistent

Microsoft-hosted agents are the simplest way to run the pipeline as the maintenance is taken care of.

Self-hosted agent:

In case the application requires a variety of dependent software to build and release or we need machine-level cache or persistence across pipeline runs - A self-hosted agent is an option.

self-hosted agents provided us complete control over the infra and the dependent software.

Following variants of the Agents exist based on the infrastructure in which they are installed

  • MacOS agent
  • Linux agent
  • Windows agent
  • Docker agent

Azure DevOps Agent Pool:

An agent pool represents a collection of agents. An agent is scoped at an Organization level so a pool can be shared across multiple projects.

Each pipeline will be targeted to an agent pool and Azure DevOps determines which agent has to be allocated from a pool to run a specific job.

A predefined agent pool called "Azure Pipelines" is provided with Microsoft-hosted agents.

another predefined pool called "Default" is provided where self-hosted agents can be included.

Azure DevOps Agent Specifications:

Azure DevOps agents have the following two major specifications

  • Capabilities
  • Parallel jobs


Azure DevOps agents can possess certain capabilities which define what they can do, for example -

demand from a job can be that the agent should have the capability to run Maven

demand from a job and capabilities of an agent should have an exact match

Parallel jobs:

Parallel jobs define the number of pipeline jobs that can run simultaneously in an Azure DevOps organization

If there is only one parallel job - the second and further run of the jobs will have to wait in a queue until the first job is completed

depending on the concurrency required, we might need to purchase additional parallel jobs

Parallel jobs can be used with Microsoft-hosted or self-hosted agents

for Microsoft-hosted parallel jobs - we can get up to 10 free parallel jobs that can run upto 6 hours each time in the case of public projects

for private projects, we can get a free job that can run upto 60 mins each time (with 30 hours monthly cap)


azure devops agent summary

We saw an overview of Azure DevOps agents and their types , in the next week - we will see a bit more in detail.

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Written by Thillai Madhavan who lives and works in India. Stay updated by following him on LinkedIn.

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