The Top 10 REST Architecture Interview Questions to Prepare For

Representational State Transfer (REST) has become the standard for building API-driven applications. As a result, knowledge of REST principles is a must-have skill for any developer or IT professional working with modern web services and APIs.

This article will talk about the best REST architecture interview questions that will show how well you understand basic REST ideas. Mastering the fundamentals will help you design scalable, flexible, and maintainable REST APIs.

What is REST and Why is it Used for API Design?

When you use hypermedia to build distributed systems, you can use REST or RESTful architecture. It uses existing HTTP protocols and infrastructure to let loosely coupled, independent parts talk to each other without any problems.

REST is commonly used for API design because of its simplicity, flexibility, and scalability. It uses standard HTTP methods like GET, POST, PUT, DELETE to perform operations on resources. Resources are identified by URIs (Uniform Resource Identifiers).

With REST we build our API around resources. These resources represent the nouns of the system – things like users, products, orders. We expose these resources through endpoints which accept HTTP requests and return appropriate responses.

This approach aligns perfectly with the needs of an API-first architecture. Because the client and server are separate, they can grow and change on their own. The uniform interface makes REST APIs easy to understand and integrate with. Statelessness and caching optimize performance.

However, REST may not be suitable for systems requiring real-time updates, transactions, or advanced server-side business logic. The simplicity of REST can also result in an explosion of endpoints to cover every use case.

What is a REST Resource?

A resource is the central concept in any RESTful API. It represents an object or information that clients interact with. Resources have unique identifiers in the form of URIs.

For example, in an e-commerce API, specific products would be resources with a URI like /products/12345. The collection of all products would be /products.

Resources can have multiple representations like JSON, XML, HTML. Clients can specify desired representation through content negotiation.

Resources should be modeled around business entities and follow a consistent naming convention. Nested or related resources can be expressed through hierarchical URIs like /customers/1234/orders.

Properly modeling resources is key to creating intuitive, scalable APIs. Resources form the nouns of the API while HTTP methods provide the verbs.

What is a URI in REST?

URI or Uniform Resource Identifier is a unique address that identifies a resource on the internet. It provides a simple and extensible naming mechanism for abstract resources.

In a RESTful API, URIs represent the address of the resources that clients interact with. For example, to get information about customer 123 in an API, we would send a GET request to a URI like:

/api/customers/123

URIs should be based on nouns and not actions. They should use hierarchical structure to denote relationships.

URIs identify resources – they do not specify details about resource representations or the actions performed on them. This decoupling of identifier from interaction details is a key REST principle that enables independent evolution.

What are the Key Features of REST APIs?

Some of the defining features of REST APIs include:

• Statelessness – No client session state is stored on the server between requests. Each request contains full details for the server to process.

• Cacheability – REST responses must define if and how they can be cached to enhance performance.

• Uniform Interface – Resources are manipulated through fixed set of four operations using HTTP methods – GET, POST, PUT, DELETE.

• Layered System – REST allows you to use a layered system architecture where components can be independently modified or replaced.

• Code on Demand (Optional) – Servers can optionally send executable code like Javascript to clients.

The uniform interface, statelessness, and focus on resources make REST APIs flexible, performant and easy to maintain. The layered architecture promotes loose coupling between components.

What is Statelessness in REST and How Does it Affect Scale?

Statelessness is a core REST constraint that requires the server not to store any client state between requests. Complete request details must be supplied by the client each time.

This improves scalability since the server does not have to manage client sessions, reducing server memory usage. Servers can quickly free up resources once the request is processed. Statelessness also enables any server instance to handle any client request since no contextual information needs to be stored on the server between requests.

However, statelessness adds a small bandwidth overhead as complete request details need to be sent in each request rather than just session IDs. It may also impact user experience in applications that expect real-time server communication. Workarounds like server-side caching can alleviate these limitations.

What is JAX-RS and How Does it Relate to REST?

JAX-RS or JSR-311 is a Java API specification that provides support for RESTful web services. It simplifies the process of creating REST APIs in Java through a set of annotations and best practices.

Some ways JAX-RS relates to REST:

• It uses annotations like @Path, @GET, @POST to map Java methods to REST resources and HTTP actions.

• It automatically converts objects like collections to desired response formats like JSON.

• It handles HTTP requests and responses, freeing developers to just focus on business logic.

• Provides exception mapping from application exceptions to appropriate HTTP responses.

Overall, JAX-RS reduces boilerplate code and enforces REST principles to create consistent, well-architected REST APIs in Java.

What are HTTP Status Codes and How are They Used?

HTTP status codes are 3-digit codes returned in HTTP responses that indicate the status of the requested operation. They define whether a request was successfully processed or not.

Some common HTTP status codes are:

• 2xx – Success codes like 200 (OK) and 201 (Created)
• 3xx – Redirection codes like 301 (Moved Permanently)
• 4xx – Client error codes like 400 (Bad Request) and 404 (Not Found)
• 5xx – Server error codes like 500 (Internal Server Error)

In REST APIs, status codes indicate the result of the client’s request. 200 indicates success, 404 signifies resource not found, 400 implies a malformed request, and 500 denotes a server-side error.

REST APIs use status codes instead of exceptions to decouple response status from actual response body. This enables cleaner separation of concerns on the server side.

What are the Common HTTP Methods Used in REST APIs?

The common HTTP methods used in REST APIs are:

• GET – Used to retrieve a resource
• POST – Used to create a new resource
• PUT – Used to update an existing resource
• PATCH – Used to partially update a resource
• DELETE – Used to delete a resource

This standardized, constrained set of operations makes REST APIs easy to understand and use. The meaning of each verb is unambiguous for both developer and client.

GET, HEAD, OPTIONS and TRACE methods are safe – they don’t modify resources. POST, PUT, PATCH and DELETE are idempotent meaning calling them once is equivalent to calling them multiple times.

What is HATEOAS and How Does it Relate to REST APIs?

HATEOAS or Hypermedia as the Engine of Application State is a constraint of REST that allows clients to interact with a service entirely through dynamically provided hypermedia.

This means REST clients only need to understand the initial URI of the app. All further actions the client can take are discovered within resource representations returned from the server. This is enabled through hyperlinks included in responses.

For instance, a GET request to /customers/123 may return a customer resource representation containing links for update and delete operations. The client does not need any prior knowledge of these links to use them.

HATEOAS facilitates loose coupling and encapsulation in REST APIs. Client code only needs to understand the fixed interface and no application internals. It enables self-descriptive messages returned from the API.

How Do You Version REST APIs?

Some common approaches to version REST APIs include:

• URI Versioning – Include the version number in the URL like v1/customers
• Request Parameter – Pass a version parameter like /customers?version=1.0
• Custom Header – Use a custom header like X-API-Version with the request
• Media Type Versioning – Use versioning content types like application/vnd.myapi.v1+json

Each approach has trade-offs. URI versioning is clean but creates more endpoints. Custom headers and request parameters add complexity. Media type versioning allows content negotiation but clients may not always support it.

Ideally, versioning schemes should be backward compatible and not break existing clients. New versions should be additive and expanded, not modifying existing behavior.

What are the Challenges in REST API Error Handling?

There are a few key challenges with error handling in REST APIs:

• REST uses status codes instead of exceptions so developers have to shift mindset from try/catch blocks.
• Additional code is needed to manually map application exceptions to appropriate HTTP status codes.
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