Azure DevOps REST APIs: 6 Comprehensive Aspects

on CRUD, HTTP, Microsoft Azure, REST API, SaaS, Tutorials • October 29th, 2021 • Write for Hevo

Azure DevOps REST API FI

In today’s competitive business environments and growing customer demand, companies strive to deliver reliable software for offering a better customer experience. Product creation requires enterprises to practice efficient cooperation and communication between the Development and IT (Information Technology) Operations team. DevOps fosters collaboration, focuses on improvements, and streamlines development pipeline processes for a superior software development cycle. As Azure DevOps provides REST (Representational State Transfer) API (Application Programming Interface) services for organizations, it helps create robust applications with integrated features to scale globally by hosting services.

This article describes the working of Azure DevOps REST APIs. It introduces you to the fundamentals of REST API and Azure DevOps. The article also explains various limits and best practices to follow while using Azure DevOps REST APIs. Let’s get started.

Table of Contents

Prerequisites

You will have a much easier time understanding the Azure DevOps REST APIs if you have gone through the following prerequisites:

  • Working knowledge of REST API.
  • Working knowledge of HTTP methods.

Introduction to Azure DevOps

Azure DevOps Logo
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Azure is a cloud-computing platform from Microsoft that provides solutions including Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS), and Software-as-a-Service (SaaS). Since Azure DevOps is a subset of Microsoft Azure, it is a SaaS platform that manages entire software development projects.

At its core, Azure DevOps offers five services including Azure Boards, Azure Pipeline, Azure Repos, Azure Test Plans, and Azure Artifacts for application lifecycle management. Azure DevOps not only serves Azure DevOps Server (previously Team Foundation Server) for on-premise deployment but also provides cloud-based DevOps service to power any DevOps pipeline.

Key Features of Azure DevOps

Azure DevOps extends a suite of tools to provide end-to-end solutions for software process management. It delivers greater value to businesses. Some of the key features of Azure DevOps include:

  1. Collaboration: Collaboration allows Azure DevOps to host and manage code centrally. With Azure Board service, teams become more efficient using the Kanban or Scrum system for Project Planning, Dashboard Analysis, and Reporting Abilities. As collaboration ensures the development team remains agile, businesses deliver better end products that eventually satisfy client needs and customer concerns.
  2. Integration: Integration helps organizations to get better control of processes and workflows. With the Azure Pipeline service, the necessary environments required for coding can be provisioned within minutes. Creating a pipeline allows Continuous Integration and Continuous Deployment (CICD) to ship software quickly and efficiently.
  3. Reliability: Reliability is achieved by giving cohesive solutions to complex problems. As Azure DevOps provides enterprise-grade security, it can handle deployment across multiple instances as well as keep applications within compliance.

To know more about Azure DevOps, visit this link.

Introduction to REST API

REST API Logo
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A REST API is an Application Programming Interface (API) that adheres to REpresentational State Transfer architecture. With REST APIs, Developers integrate applications with higher flexibility and lightweight techniques. Today, it has emerged as the most widely used method for connecting components in microservices architectures.

REST API allows an application or service to access resources within another application or service, given it follows below REST design principles:

  1. Decoupled Service: Decoupled Service describes the nature of the separation between client and server. A service possesses multiple capabilities while listening to requests, and any request made by consumers is either accepted or rejected by the server.
  2. Statelessness: Statelessness constraint mandates each ‘request’ to include all necessary information requested by clients without storing any context on the server.
  3. Cache: Cache helps to mitigate constraints of statelessness. If a response is cacheable, the client cache is given the right to reuse that response data for later, equivalent requests.
  4. Uniform Interface: REST API provides a uniform interface to users. Irrespective of where a request was initiated, all API requesting the same resource should look alike (Idempotent).
  5. Layered System: Layered System constraint limits the interaction of components beyond the immediate layer.

To know more about REST API, visit this link.

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Key Components of Azure DevOps REST APIs

Azure DevOps REST APIs are service endpoints that support HTTP (Hypertext Transfer Protocol) methods to provide CRUD (Create, Read, Update, and Delete) access for desired resources. The client ‘requests’ for application or service, whereas the server gives a ‘response’. Below are the key components of Azure DevOps REST APIs request and response:

  1. Request URI (Uniform Resource Identifiers)
  2. Request Message Header
  3. Request Message Body
  4. Response Message Header
  5. Response Message Body

1) Request URI (Uniform Resource Identifiers)

A Request URI consists of the following syntax in general:

Syntax:VERB https://{instance}[/{team-project}]/_apis[/{area}]/{resource}?api-version={version}

A Request URI consists of three parameters as mentioned below:

  1. Instance: It is a request that is either sent to Azure DevOps Services or the TFS (Team Foundation Server) server. They are structured as shown below:
Azure DevOps Services:dev.azure.com/{organization}
TFS:{server:port}/tfs/{collection}
  1. Resource path: It is the complete address of a resource.
Syntax:_apis/{area}/{resource}
  1. Api-version: It refers to the practice of managing changes transparently to avoid your application or service break as APIs evolve.
Syntax:{major}.{minor}[-{stage}[.{resource-version}]]

2) Request Message Header

A Request Message Header comprises an HTTP method that tells a service what operation you desire to perform. Azure DevOps REST APIs support GET, HEAD, PUT, POST, and PATCH methods. Optionally, an additional header field is provided to authorize requests. For instance, if a client logs into a bank account, a user is prompted with a token for a specified URI and HTTP method using an authorization header.

3) Request Message Body

Request Message Body is an optional field used to support the URI and HTTP operation.

4) Response Message Header

Response Message Header allows additional information to pass from the server after receiving and interpreting a request message.

5) Response Message Body

Response Message Body is an optional HTTP field used to carry the entity-body associated with the response. In general, MIME (Multipurpose Internet Mail Extensions) encoded objects are returned in a structured format (JSON or XML), as indicated by the ‘Content-type’ response header. 

Examples of Azure DevOps REST APIs

Azure DevOps integrates with custom applications or services to make direct HTTP calls using REST API. It not only interacts with your application but also allows integration with other popular third-party services such as Slack or Jenkins.

Suppose you want to get a list of projects for your organization via Azure DevOps REST API, it involves the authentication of users via an interactive prompt to return a list of projects inside a selected Azure DevOps account. A Personal Access Token (PAT) is often used for authentication of an application that can be provided through an HTTP header. You can use C# to convert PAT into a Base64 string and get the required list of all projects in an organization using the below code:

Code for Converting PAT into Base64 String
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Limits for Azure DevOps REST APIs

Azure DevOps Services is one such tool that can effectively run an organization while integrating tools between services to improve efficiency. However, automation of various tools demands a high rate of requests for the execution of tasks. The surge in requests will quickly reach a threshold value, forcing Azure DevOps Services to limit services for your organization. Below are a few limits monitored by Azure DevOps REST APIs:

  1. Rate Limits: It delays requests for individual users. Currently, Azure DevOps has a global consumption limit for personal usage exceeding 200 times the consumption of a typical user within a (sliding) five-minute window. Depending on the user’s sustained level of consumption, a delay ranging from a few milliseconds per request up to 30 seconds will be enforced.
  2. Throughput Units (TSTU): It is the average load a single normal user of Azure DevOps generates per five minutes. The global consumption limit is 200 TSTUs within a sliding five-minute window.
  3. Pipeline: It is treated as an individual entity that tracks its own resource consumption. Currently, a 200 TSTU limit for an individual pipeline in a sliding 5-minute window is the threshold, which is the same as the global consumption limit for users.
  4. Projects: It represents an actual container where necessary data is stored. Azure DevOps Services limits each organization to 300 projects per organization. Above 300 projects, enterprises experience connection degradation when connecting to Visual Studio.
  5. Work items: They are the objects used to track projects. 

Below are the operational limits for Azure DevOps REST API:

ObjectLimit
Long text field1 M characters
Work item tags assigned to a work item100
Work item links assigned to a work item1000
Attachments added to a work team100
Attachment size60 MB
Query execution time30 seconds
Query results20,000 items
Query length32,000 characters
Shared queries under a folder999 queries

Best Practices for Azure DevOps REST APIs

Like many SaaS solutions, Azure DevOps Services leverages multi-tenancy architecture to enhance Scalability, Performance, and a Cost-Effective solution. However, multi-tenancy is inherently vulnerable to performance issues. Azure DevOps Services enforces ‘rate limits’ to limit resources an individual can consume and the number of requests for certain commands. If the limits are exceeded, requests may either be delayed or blocked. Following are some of the best practices followed while using Azure DevOps REST APIs:

1) Push only Actionable Work Items

It is recommended to prioritize actionable items before pushing them into Azure DevOps Services. If your team plans to engage/address actions for the future, do not keep such work items inside Azure DevOps Service unless necessary.

2) Maintain your own Data Store

As Azure DevOps Services is not designed as a data storage service, it is suggested to maintain your own Data Store and not have all items in one place.

3) Batch your Changes

As performing single operations is slow and expensive, batching helps to improve performance and rate-limiting issues by combining several calls into a single call.

4) Limit your Revisions

Often businesses release various versions of a single work item to solve bugs. However, performing many revisions may result in performance problems. It is recommended to reduce updates by batching field changes and keeping a minimum number of revisions to avoid revision limits.

5) Handle Failures Gracefully

While consuming Azure DevOps REST APIs, Developers must ensure code to handle failures. As soon as a resource limit or frequency of utilization crosses a threshold, updates and queries fail. For instance, a query that runs longer than 30 seconds will return an error as shown below:

Error Message
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Conclusion

Azure DevOps REST API is independent of language or library, ensuring applications and services continue to work as APIs evolve. The amalgamation of development (Dev) and operations (Ops) enables rapid development of applications with easier maintenance of deployments in organizations. 

This article gave you a brief introduction to Azure DevOps REST APIs along with their key features. It also provided in-depth knowledge about Azure DevOps REST APIs’ key components, examples, limits, and best practices. You may now easily implement the Azure DevOps REST APIs.

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