Which API Architecture Fits Your Project? A Deep Dive into RPC, SOAP, REST, and GraphQL

This article discusses the four main API architectural styles, compares their pros and cons, and highlights the most suitable style for each scenario.

1. RPC: Call functions on another system

Remote Procedure Call (RPC) allows functions to be executed remotely across different contexts, extending the concept of local calls into the HTTP API world.

Early XML‑RPC had data‑type issues, leading to the more specific JSON‑RPC and later gRPC, which adds load‑balancing, tracing, health checks, and authentication, making it ideal for connecting microservices.

RPC Working Mechanism

The client serializes parameters and metadata into a message, sends it to the server, which deserializes, executes the operation, and returns the result; both sides handle serialization.

RPC Advantages

Simple direct interaction. Uses GET for retrieval and POST for other operations, reducing calls to endpoint invocations.

Easy to add new functions. New requirements can be met by adding a new endpoint and function.

High performance. Lightweight payloads reduce network pressure, enabling efficient massive message exchange between services.

RPC Disadvantages

Tight coupling with underlying systems. Strong coupling reduces reusability and can expose internal implementation details, raising security concerns.

Low discoverability. APIs lack self‑describing documentation, making it hard to know which function to call.

Function explosion. Easy addition of functions can lead to overlapping, hard‑to‑understand APIs.

RPC Use Cases

Large companies like Google, Facebook (Apache Thrift), and Twitch (Twirp) use high‑performance RPC for internal microservice communication where low‑overhead messaging is critical.

Command‑oriented APIs such as Slack benefit from RPC‑style design for concise, action‑focused endpoints.

2. SOAP: Make data available as a service

SOAP is an XML‑based, highly standardized network communication protocol that emerged after XML‑RPC and was later eclipsed by REST.

SOAP Working Mechanism

SOAP messages consist of an envelope, a body (request or response), a header for protocol or additional requirements, and a fault element for error reporting.

Envelope tag to start and end each message

Body containing the request or response

Header indicating protocol compliance or extra requirements

Fault element describing any errors

SOAP APIs are described using WSDL, which defines endpoints and available operations, enabling language‑agnostic client generation.

SOAP Advantages

Language and platform independence. Built‑in web service creation lets SOAP handle messages across diverse environments.

Binding to various protocols. Flexible transport options suit many scenarios.

Built‑in error handling. XML fault messages include error codes and descriptions.

Security extensions. Integration with WS‑Security provides confidentiality, integrity, and authentication for enterprise transactions.

SOAP Disadvantages

XML‑only payloads. Verbose messages increase bandwidth usage.

Heavy weight. Large XML files demand substantial network resources.

Steep learning curve. Implementing SOAP requires deep knowledge of protocols and strict specifications.

Rigid message structure. Adding or removing fields is cumbersome, slowing adoption.

3. REST: Make data available as resources

REST is a widely adopted API style defined by a set of architectural constraints, originating from Roy Fielding’s doctoral dissertation.

REST Working Mechanism

RESTful systems should obey six constraints: uniform interface, statelessness, cacheability, client‑server separation, layered system, and code‑on‑demand.

Uniform interface: same interaction method regardless of client or device.

Stateless: each request carries all necessary state.

Cacheability.

Client‑server architecture: independent evolution.

Layered system.

Code‑on‑demand capability.

While some services are only partially RESTful, true REST emphasizes hypermedia (HATEOAS) to provide discoverable links in responses, decoupling client and server.

REST Advantages

Client‑server decoupling. Enables independent evolution and stable interfaces.

Discoverability. Communication description is self‑contained, eliminating external docs.

Cache friendliness. Leverages HTTP caching mechanisms.

Multiple format support. Works with JSON, XML, and others.

REST Disadvantages

No standard structure. Resource modeling varies, making practical implementation challenging.

Large payloads. Rich metadata can be verbose, problematic for bandwidth‑constrained environments.

Over‑ or under‑fetching. Responses may contain too much or too little data, requiring additional requests.

REST Use Cases

Management APIs benefit from strong discoverability and documentation. Simple resource‑driven applications also fit well with REST.

4. GraphQL: Request only the data you need

GraphQL was created to reduce the multiple calls required by REST, allowing precise data requests.

GraphQL Working Mechanism

It starts with a schema that defines all possible queries and their return types, using a strongly typed schema definition language (SDL). Clients validate queries against the schema, and the server resolves them, returning only the requested data.

GraphQL also supports subscriptions for real‑time notifications.

GraphQL Advantages

Typed schema. Improves discoverability by exposing available queries.

No versioning. A single evolving schema eliminates the need for versioned APIs.

Detailed error messages. Errors pinpoint the exact failing resolver.

Flexible permissions. Selectively expose data, unlike REST’s all‑or‑nothing approach.

GraphQL Disadvantages

Performance concerns. Deeply nested queries can overload the system; for complex queries, REST may be more efficient.

Cache complexity. Lacks native HTTP caching semantics, requiring custom solutions.

Steep learning curve. Understanding SDL and schema design demands significant effort.

GraphQL Use Cases

Mobile APIs. Optimizes payload size for limited bandwidth.

Complex systems and microservices. Aggregates data from multiple sources into a unified schema, easing legacy integration.

5. Which API pattern best fits your use case?

Each API project has unique constraints and requirements. Choosing an architecture depends on the programming language, development environment, and resource budget.

The tightly coupled RPC style suits internal microservices but is unsuitable for public APIs.

SOAP’s heavyweight nature and strong security extensions make it ideal for billing, reservation, and payment systems.

REST offers the highest level of abstraction and is great for management APIs, though it can be verbose for mobile scenarios.

GraphQL advances data fetching efficiency but requires time and expertise to master.

Ultimately, experiment with a small use case to see if a particular API style solves your problem before scaling it up.

Original source: https://levelup.gitconnected.com/comparing-api-architectural-styles-soap-vs-rest-vs-graphql-vs-rpc-84a3720adefa