1. Introduction
The way in which distributed systems communicate with each other is crucial to their efficiency, reliability, and overall functionality. REST (Representational State Transfer) and RPC (Remote Procedure Call) are prominent communication paradigms.
REST and RPC allow different systems or components to talk to each other. However, they have fundamental differences in philosophy, design, and application.
This tutorial highlights the differences between REST and RPC, uncovering their histories, principles, advantages, and disadvantages.
2. Historical Context
The differences in the origins of REST and RPC highlight the evolution of web communication and emphasize the challenges and environments each was designed to address.
2.1. Short History of RPC (Remote Procedure Call)
The concept of RPC dates back to the early days of distributed computing. Systems needed a way to execute procedures or functions on remote machines, essentially making a call as if it were a local procedure.
The RPC systems began taking shape in the 1980s with the introduction of SunRPC, developed by Sun Microsystems. As the internet evolved, RPC’s capabilities grew. This led to the development of variations like XML-RPC, which allowed for remote calls using XML over HTTP and later JSON-RPC.
RPC has gained popularity nowadays with protocols like gRPC, which combines HTTP/2 and Protocol Buffers to deliver highly efficient remote calls.
2.2. Emergence of REST (Representational State Transfer)
Dr. Roy Fielding introduced REST in his 2000 doctoral dissertation. Instead of focusing on actions or methods, as in RPC, REST centers on resources. Fielding emphasized using the web’s inherent capabilities, particularly HTTP’s stateless requests and standardized methods.
Given its simplicity and alignment with the web’s principles, REST quickly gained traction. It became the standard for public APIs on the web. While RESTful principles are still highly prevalent, there’s a growing movement towards more flexible and efficient protocols, especially in specific use cases where REST might not be optimal.
3. Basic Definitions
Let’s overview the basic definitions and characteristics of both REST and RPC.
3.1. REST
REST is an architectural style. It provides a set of constraints that enable systems to achieve properties like performance, scalability, and modifiability.
At its core, REST is about representing and manipulating resources on the web. A resource can be anything – an object, a service, a piece of data – and it’s uniquely identified by its URI.
RESTful Constraint
Description
Client-Server Architecture
This dictates a separation between the client (UI) and server (data storage), promoting independent evolution.
Statelessness
Each request from a client contains all the information needed to process it. There’s no session context on the server.
Cacheability
Responses must define themselves as cacheable or non-cacheable to improve client-side performance.
Layered System
A client cannot ordinarily tell whether it is connected directly to the end server or to an intermediary.
Code on Demand (Optional)
Servers can extend client functionality by transferring executable code.
Uniform Interface
Simplifies the architecture by having a consistent interface, which is fundamental to the RESTful design.
3.2. RPC
RPC is a protocol that a program can use to request a service from a program located on another computer. It allows a program to cause a procedure or subroutine to execute on another address space, usually another computer on a shared network. It’s similar to calling a method on an object that exists on a different machine.
RPC Type
Description
XML-RPC
Uses XML to encode its calls and HTTP as a transport mechanism.
JSON-RPC
Similar to XML-RPC but uses the JSON format, making it lighter.
gRPC
An open-source RPC framework from Google, using Protocol Buffers for serialization and running over HTTP/2.
4. Communication Model
The way in which data is transferred, and the conventions used for such communication differentiate REST and RPC significantly. Let’s dissect the respective communication models of each.
4.1. REST
REST harnesses the power and simplicity of the HTTP protocol for communication, relying on its standardized set of methods. These standard HTTP verbs ensure uniformity and predictability in interactions.
Due to stateless communication, each request from a client to a server must contain all the information needed to understand and process the request. This makes interactions clear-cut, without any need to maintain a session state on the server.
CRUD operations
HTTP verbs
GET
Retrieve a resource.
POST
Create a new resource.
PUT/PATCH
Update an existing resource.
DELETE
Remove a resource.
4.2. RPC
RPC’s model is more about invoking actions. Its method calls are more verbose, indicating specific procedures.
RPC is like calling a function. The client specifies the procedure to execute along with the parameters, and the server returns the results. This might appear more direct and granular compared to the resource-based approach.
RPC Element
Description
Method Name
The specific procedure or function to invoke.
Parameters
The arguments required for the function.
Return Value
After execution, the procedure returns a value to the client.
An essential aspect to note is that RPC might seem tightly coupled because of its procedural nature. Modern implementations like gRPC are built with flexibility and efficiency in mind, allowing for more scalable and loosely coupled systems.
5. Addressing Resources
How systems identify and address the data or services they interact with is central to their design and functionality. The paradigms of REST and RPC have distinct ways of approaching this.
5.1. REST
In the RESTful world, everything revolves around the concept of resources. Every resource in a RESTful system is uniquely identified by its URI. This design choice provides a straightforward way to locate, manipulate, and interact with entities on the web.
In REST, it’s not just about identifying the resource but also about how we represent it. Common representations include JSON and XML, among others. The idea is to interact with the resource using these representations via standard HTTP methods.
5.2. RPC
RPC revolves around invoking procedures or methods. In RPC, we call a specific method provided by the server. The method name and parameters are central to the request. There’s no standard like URIs in REST. Instead, the method name and its signature become the defining aspect.
Parameters can be passed by name or by position, and the method naming usually mirrors the function it’s trying to achieve on the server side. While this can be seen as flexible, it can also lead to challenges with versioning and changing method signatures over time.
6. Data Formats
The representation and structure of data being transmitted play a pivotal role in the clarity, efficiency, and performance of communication. Both REST and RPC employ different strategies for this.
6.1. REST
REST is agnostic to the data format, but there are popular conventions that have been widely adopted in the industry. The majority of RESTful services use JSON due to its lightweight nature and ease of use. XML was more prevalent in earlier implementations, especially with SOAP-based services, but has seen a decline in favor of JSON.
The beauty of REST is that we can choose the representation that best fits our needs. For instance, while JSON and XML are common, some systems might use YAML, HTML, or even custom formats.
6.2. RPC
The data format in RPC largely depends on the type and specifications of the RPC protocol being used.
RPC type
Data Format
XML-RPC
As the name suggests, XML is the primary data format.
JSON-RPC
TUses JSON for its calls.
gRPC
Utilizes Protocol Buffers (often shortened to Protobuf), a highly efficient and compact serialization format developed by Google.
In newer RPC protocols like gRPC, performance is strongly emphasized. Protobuf, for example, is smaller and faster than JSON and XML. This can lead to significant performance gains, especially in systems with high-throughput requirements.
7. Comparing REST and RPC
Every architectural style or protocol has its own set of advantages and trade-offs. Understanding these can aid developers in selecting the right approach for their specific use cases.
7.1. REST
Let’s review the pros and cons of REST architecture:
Strengths
Weaknesses
Each request is self-contained.
Statelessness may require redundant data to be sent in every request.
Interactions are simple due to the utilization of HTTP methods.
Operations are limited to HTTP Methods.
Responses can be cached, enhancing performance.
Textual formats can introduce overhead, especially for large payloads.
Platform independent and promotes interoperability.
7.2. RPC
Also, we can list same advantages and disadvantages of RPC as well:
Strengths
Weaknesses
Can be tailored to specific needs with its function-based approach.
Changes in the server-side procedure could break clients.
Protocols like gRPC with Protocol Buffers can be very efficient.
Might add complexities due to tooling, debugging, and setup.
Support bidirectional streaming, opening doors for real-time applications.
Not all RPC protocols are based on HTTP, which complicates web-based interactions.
8. Conclusion
To conclude, neither REST nor RPC is a silver bullet. They cater to different needs and scenarios, and understanding their strengths and limitations is crucial. The right choice often emerges from a thorough analysis of our project’s requirements, objectives, and potential evolutions.