This content originally appeared on Level Up Coding - Medium and was authored by TechFarm by Shahz
APIs are the backbone of modern web and mobile applications, connecting the front-end with the back-end and enabling seamless communication between the two.
But with the increased popularity of APIs, security and scalability concerns have become more pressing. How can you ensure that your API will perform as expected and be secure from potential threats?
The answer lies in the design phase. A well-written and comprehensive Technical Design Document (TDD) lays the foundation for a successful API project and helps to mitigate potential risks.
In this blog, we’ll take a closer look at the process of writing a TDD for an API hosted in Azure Functions, a popular platform for hosting and scaling cloud-based applications.
What is a Technical Design Document (TDD)
A Technical Design Document (TDD) typically includes a high-level overview of the solution, as well as more detailed technical specifications and architecture diagrams. It provides a complete picture of the technical implementation of the solution, including all components and how they interact with each other.
It defers from Low-Level Design Document (LLD) as such that an LLD focuses on a specific part of the solution and provides a more detailed view of its design and implementation. It often includes class diagrams, sequence diagrams, and other technical specifications that provide a clear understanding of the implementation of that part of the solution.
Capturing all aspects of an API in a TDD
While writing a TTD we must keep in mind that the purpose of that design document is to help ensure that everyone involved in the project is on the same page and has a clear understanding of the requirements, architecture, and implementation details of the API.
A typical technical design document for an API might include the following information:
- Introduction: A brief overview of the API, including its purpose, scope, and target audience.
- Requirements: A list of functional and non-functional requirements for the API, including any performance, security, or availability constraints.
- Architecture: A high-level overview of the API’s architecture, including a description of the components and their relationships, as well as a diagram or flowchart that provides a visual representation of the architecture.
- Data Model: A description of the data structures and data models used by the API, including any data fields, data types, and data relationships.
- API Endpoints: A list of all API endpoints, including their URLs, supported HTTP methods, and a description of the input and output data for each endpoint.
- Authentication and Authorization: A description of the authentication and authorization mechanisms used by the API, including any security protocols, access controls, or user roles and permissions.
- Error Handling: A description of how the API handles errors, including any error codes, error messages, and error response formats.
- Deployment: A description of the deployment process for the API, including any infrastructure requirements, deployment tools, and deployment steps.
- Monitoring and Troubleshooting: A description of the monitoring and troubleshooting tools and processes used to manage the API, including any performance metrics, log files, and alert mechanisms.
- Conclusion: A summary of the key takeaways from the design document, including any remaining open questions or areas for further investigation.
Documenting using Design Diagrams
Here are a few diagrams that can be useful in documenting the design of an API:
- Data Flow Diagram: A data flow diagram (DFD) can help to visualize the flow of data through the API, including the sources and destinations of data, as well as the transformations and computations performed on the data.
- Entity-Relationship Diagram: An entity-relationship diagram (ERD) can help to model the relationships between the data entities used by the API, such as tables in a database or objects in a object-oriented programming language.
- Sequence Diagram: A sequence diagram can help to visualize the interactions between the API and its clients, including the order and flow of messages exchanged between the components.
- Class Diagram: A class diagram can help to model the classes and objects used by the API, including the relationships between objects and the inheritance hierarchy of classes.
- Component Diagram: A component diagram can help to visualize the components and dependencies of the API, including the relationships between components and the inputs and outputs of each component.
Use Case: Diagrams for a API for User Login
Here’s an example of a class diagram and sequence diagram for the simple login service API to implemented using NodeJS in Azure function:
Class Diagram:
In this class diagram, we have three classes: User, Credential, and Role. The User class has two attributes, username and password, and the Credential class also has two attributes, username and password. The Role class has two attributes, name and permissions. The diagram also shows a many-to-one relationship between Credential and User, and a many-to-many relationship between Role and User.
Sequence Diagram:
In this sequence diagram, we have two participants: the client and the login service. The client sends a login request to the login service, which then validates the user’s credentials by checking them against the backend database. If the credentials are valid, the login service returns the user’s role, otherwise it returns false. Finally, the client receives the response from the login service.
Designing Error and Exception Handling
Error and exception handling are important aspects of any software system, and it is important to document these in the design document as well. Here are a few suggestions on how to show error and exception handling in a design document:
- Flowcharts: Flowcharts can be used to visualize the flow of the application, including the normal flow of execution and the error handling flow. You can use different symbols or colors to distinguish between the normal flow and the error flow.
- State Diagrams: State diagrams can be used to model the different states of the application and the transitions between states, including the transitions triggered by errors or exceptions.
- Pseudocode: Pseudocode can be used to describe the steps involved in error handling, including the conditions under which errors are raised and the actions taken to handle them.
- Exception Class Diagram: An exception class diagram can be used to model the exception classes used by the application, including the inheritance hierarchy and relationships between exception classes.
- Error Codes: A list of error codes can be used to describe the different types of errors that can occur in the system, along with a description of each error and its cause.
By documenting the error handling mechanism in the design document, it becomes easier to understand how the system will behave in case of errors, and to identify any potential issues or areas for improvement. It also makes it easier for the developers to implement the error handling mechanism, since they will have a clear understanding of what is expected of them.
Capturing API security aspects like OWASP, DDoS, etc. in the design
By addressing API security in the design document, it becomes easier to ensure that the API is secure and meets the required security standards. It also makes it easier for developers to implement the security mechanisms, since they will have a clear understanding of what is expected of them.
Here are some suggestions on how to add API security aspects like DDoS and OWASP in the design document:
- DDoS Protection: To protect against Distributed Denial of Service (DDoS) attacks, the design document should mention any rate limiting or traffic filtering mechanisms that will be implemented. This could include using a Content Delivery Network (CDN), implementing IP blocking, or using a cloud-based service to protect against DDoS attacks.
- OWASP: The Open Web Application Security Project (OWASP) provides a comprehensive list of security threats to web applications, and the design document should take these into account. You can mention which OWASP security risks the API is vulnerable to, and how you plan to mitigate those risks. For example, you can mention how input validation and sanitization will be performed to prevent injection attacks, or how access controls will be implemented to prevent unauthorized access to the API.
- Encryption: The design document should mention the encryption mechanisms used to secure data transmitted by the API, such as SSL/TLS encryption for HTTP traffic.
- Access Control: The design document should specify the access control mechanism used by the API, such as authentication and authorization. This could include the use of OAuth, JSON Web Tokens (JWT), or other methods to ensure that only authorized users can access the API.
- Logging and Monitoring: The design document should mention any logging and monitoring mechanisms that will be implemented to monitor API usage and detect any security incidents. This could include using a log aggregator, implementing auditing and monitoring of API activity, or using a security information and event management (SIEM) system.
Including Azure Function related details in the Design Document
Here are some suggestions on how to include Azure Function related details in the design document:
- Overview: Provide an overview of the Azure Function being used, including its purpose, design, and architecture. Explain how it fits into the overall API design and what it will be responsible for.
- Deployment: Mention the steps required to deploy the Azure Function and how it will be integrated into the API. This could include details about the Azure Function App, the resources required (such as storage accounts, databases, etc.), and any configuration settings that will be needed.
- Scaling: Discuss the scaling options available for the Azure Function and how they will be used to ensure the API can handle increasing traffic. Explain how the Azure Function can be scaled up or down as needed, and what factors will influence this decision.
- Monitoring: Explain how monitoring and logging will be performed for the Azure Function, including how usage and performance data will be collected and analyzed. Mention any tools or services that will be used for this purpose, such as Azure Monitor or Application Insights.
- Security: Discuss the security considerations for the Azure Function, such as authentication and authorization, data encryption, and DDoS protection. Explain how the Azure Function will be secured, and how it will be integrated with other security components of the API.
By including these details in the design document, it becomes easier to understand the role of the Azure Function in the overall API design and to ensure that it meets the required performance, scalability, and security standards.
The Bottom Line
In conclusion, writing a Technical Design Document (TDD) for an API hosted in Azure Functions is a critical step in the API development process. A well-written TDD serves as a roadmap for development and helps ensure the success of your project by providing a clear and detailed understanding of the architecture, design, and security considerations.
By following the best practices and techniques discussed in this blog, you’ll be well on your way to creating a TDD that will help guide your API development journey. Whether you’re just starting out or are a seasoned API developer, taking the time to write a TDD will pay off in the long run, providing you with a solid foundation for a successful API project.
You found this blog helpful and would like to stay up-to-date on the latest developments in API design and development, be sure to follow me on medium (https://shahtapa.medium.com). I’ll be sharing more insights, tips, and tutorials on a variety of topics related to APIs and software development. Thanks for reading!
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Designing an API with Azure Functions: A Guide to Writing a Technical Design Document (TDD) was originally published in Level Up Coding on Medium, where people are continuing the conversation by highlighting and responding to this story.
This content originally appeared on Level Up Coding - Medium and was authored by TechFarm by Shahz
TechFarm by Shahz | Sciencx (2023-02-12T17:10:05+00:00) Designing an API with Azure Functions: A Guide to Writing a Technical Design Document (TDD). Retrieved from https://www.scien.cx/2023/02/12/designing-an-api-with-azure-functions-a-guide-to-writing-a-technical-design-document-tdd/
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