7 API Integration Patterns: REST, gRPC, SSE, WS & Queues

There are multiples API integration patterns. I have already mentioned and describe some of the in different articles: gRPC vs REST, WebSockets vs SSE

This text is a kind of One Ring article — one to rule them all. I want you to have a single place where you can find a comparison of all the approaches done in clear and consistent manner. Thus, I have put here all the previous comparisons, and add some more into this text.

I will compare a total of 7 API integration patterns 10 axes.

Tools:

1. REST
2. gRPC
3. WebSockets
4. SSE
5. GraphQL
6. Webhooks
7. Message-Queue Base

Axes:

1. Communication Direction
2. Underlying protocols
3. Message Structure
4. Complexity
5. Security
6. Data size
7. Throughput
8. Latency
9. Ease of adoption
10. Tooling

Let’s start today’s journey from REST. As it is probably the most common way of building APIs I would use it as a baseline for all the comparison.

API Integration Patterns

1. REST

REST, or Representational State Transfer, is an architecture styles. It uses HTTP as the underlying communication medium thus it is stateless by nature and can benefit from all the advantages of HTTP, like caching. It can utilize both HTTP/1.1, HTTP/2.

• Shines when : you need a simple, cache-friendly, web-native API consumed by every language or tool.
• Struggles when : you need full-duplex streams or extremely low latency.

2. gRPC

gRPC is probably the most modern implementation of the relatively old concept of — Remote Procedure Call. gRPC usesGoogle’s Protocol Buffers as a serialization tool. By default, it utilizes HTTP/2 as transport medium data and exchange data in a binary format.

• Shines when : services need compact binary messages, strong typing, and bidirectional streaming.
• Struggles when : you must expose an API directly to browsers without extra tooling.

3. WebSockets

WebSockets provides a real-time bidirectional communication between a server and client with the usage of a single long-lasting TCP connection.

Thanks to this feature, the data is exchanged between interested parties in “real-time”. Each message is send as binary frame data or Unicode text. While WebSockets utilize custom protocol for most of the time it is still using HTTP for initial handshake.

• Shine when : both client and server need real-time, low-latency push in either direction.
• Struggle when : intermediaries (CDNs, firewalls) or strict request-response patterns dominate.

4. SSE

SSE is a technology that allows a web server to send updates to a web page. It is a part of HTML 5 specification and utilizes a single long live HTTP connection to send data in “real-time”. It can use both HTTP/1.1 and HTTP/2. SSE also have its unique MIME type:

text/event-stream. The important thing here is that it is can be only used for server-browser communication.

• Shines when : the server pushes one-way event streams to browsers with a minimal setup.
• Struggles when : you need client-to-server push or non-browser consumers.

5. GraphQL

GraphQL is a query language for your API. It allows clients to request only the subset of data they need. The client knows the server’s endpoint, the endpoint provides a schema. The schema defines the communication protocol, inputs and outputs. The request, is validated with the schema, thus malformed request woulds be rejected by the server with a proper error message.

• Shines when : clients must trim over-fetching and compose rich queries from one endpoint.
• Struggles when : the workload is write-heavy or teams cannot maintain a strict schema discipline.

6. Webhooks

Webhooks address the question — Has anything changed yet?. It is a push-style HTTP callback that lets another service tell your app when something relevant happens. It works in, in “real” time, no polling, no sockets, just an outbound POST.

• Shines when : you want lightweight server-to-server notifications without polling.
• Struggles when : delivery guarantees must be exactly-once, or the receiver is offline for long periods.

7. Message-Queue

The message queue base approach uses a middleware as a way to communicate between services. Usually in form of some platform like Kafka or RabbitMQ. The main idea behind message queues is to provide asynchronous communication. Messages are sent to a queue, which acts as a buffer between the sender and receiver. This decouples the sender and receiver and allows them to operate independently of each other.

• Shine when : you need high-throughput, decoupled, async processing with a replay.
• Struggle when : you require simple, stateless request-response or openly exposed public APIs.

API Integration Patterns – Comparison

Below is the most important takeaway from this article. For traits scaled from Very Low to Very High I am using REST a baseline. Thus, for example if one the complexity of the tools is described as Very High you can think of it as far more complex then REST.

Technology	Communication Direction	Underlying Protocols	Message Structure	Complexity	Security²	Data Size	Throughput	Latency	Ease of Adoption	Tooling
REST	Unidirectional	HTTP/1.1 or HTTP/2	Mostly JSON or XML (text)	Very Low	HTTPS	Large	Moderate	High	Very High	Extensive (Postman, Swagger/OpenAPI, cURL)
gRPC	Unidirectional or Bi-directional	HTTP/2	Protocol Buffers (binary)	Moderate	mTLS	Very Small – binary	Very High	Very Low	Moderate but growing	Decent (gRPCurl, Postman)
WebSockets	Bi-directional	WebSocket (upgrade from HTTP/1.1 or HTTP/2)	Text or binary frames	Low	WSS	Small – binary frames	High	Very Low	Moderate	Good
SSE (Server-Sent Events)	Unidirectional	HTTP/1.1	text/event-stream (UTF-8)	Very Low	HTTPS	Moderate – plain text	Moderate	Low	Moderate	Good
GraphQL	Unidirectional, Bi-directional with subscriptions	HTTP/1.1, HTTP/2; WebSocket for subscriptions	JSON (text)	Moderate	HTTPS	Large	Variable; fewer round-trips	Medium–high	Moderate but rapidly growing	Very Good (Apollo, GraphiQL)
Webhooks	Unidirectional	HTTP/1.1 or HTTP/2	JSON, form-encoded, or custom	Low	HTTPS	Large	Depends on event volume (bursty)	Moderate	Very High	Good (ngrok, request-bin)
Message-Queue	Unidirectional	Kafka TCP, AMQP, MQTT, NATS, …	Binary records, Avro, JSON …	Very High	ACLs, TLS	Small to medium – highly tunable	Very High	Very Low	Low	Extensive

Summary

There are no good or bad here, nor any silver bullets, it just a couple of tools you can use.

Nonetheless, if you want to know my recommendations here they are:

Scenario / Tech	REST	gRPC	WebSockets	SSE	GraphQL	Webhooks	Message Queue
Mobile → backend	✓	✓			✓		✓
IoT / edge device		✓	✓				✓
Service-To-Service	✓	✓	✓		✓	✓	✓
Browser push / live UI			✓	✓
3rd integration	✓				✓	✓
Streaming pipelines							✓

Remember, if you will be building anything more complex then a very focus microservice the odds are that you will be using more than one approach. Mixing different tools the get the best design is part of our daily struggle just please do not overengineer your solution.

Thank you for your time.

May also interest you:

• ArchUnit
• Distributed Systems

Blog 7 API Integration Patterns: REST, gRPC, SSE, WS & Queues from Pask Software.