How microservices communicate with each other?

In the journey of software architecture fundamentals, I often wonder, how microservices communicate with each other. I dug deep and found some answers. Here in this article, I am going to share the details I found and will see various communication patterns microserver setups generally use to communicate.

In Short

  • 🤝 HTTP-based synchronous communication enables straightforward interactions between microservices
  • Asynchronous HTTP communication avoids blocking and speeds up microservices
  • gRPC enables efficient, real-time communication between microservices
  • 📮 Message queues like RabbitMQ enable asynchronous message passing
  • 🗣 Pub/Sub model allows broadcasting messages to subscribed services
  • 💡 Event-driven communication enables dynamic reactions to state changes

HTTP-based Synchronous Communication

Synchronous communication is very effective if handled properly. Generally, we call to 3rd party or some internal APIs using HTTP calls. Generally, we use some HTTP methods, like, GET, POST, PUT, PATCH, DELETE, OPTIONS, etc. Each method applies to different scenarios. But the main fundamental of synchronous communication is system does wait for the response to come from the APIs, then only it continues to its next task.

Advantages:

  1. Ease of Understanding: HTTP-based synchronous communication is the most simple implementation, which makes it easy to understand for the developers and the stakeholders as well.
  2. Statelessness: As per the good code guidelines, APIs should be stateless, meaning, two API calls may share data but can be called without any dependency on each other. Yeah if one API is giving some data which you are sending to the second API that is another thing! But if you have the data, you are free to call them.
  3. Caching Benefits: HTTP responses can be cached for a certain period or until any data changes happen. Systems like Redis is widely been used for caching. It makes your system a lot faster as the output data can be fetched without executing the business logic most of the time.
  4. Well-Established Protocol: HTTP is a widely adopted and standardized communication protocol. You won’t get many issues working with other teams and infrastructures.

Disadvantages:

  1. Resource Consumption: Synchronous HTTP calls wait for the call to end and response to come. However, this process holds the system’s resources and demands more RAM and CPU. 
  2. Dependency Hell:  If we need to call 4 APIs, and each API takes 1 second to give a response! Now with synchronous setup, you can not proceed to the next API which one API call is going on! This makes the calls dependent on each other it is commonly referred to as “dependency hell”.
  3. Decreased Performance: As the system is waiting for API calls to complete, we are not utilizing the system optimally. This eventually makes the system slow and decreases the overall performance.
Async vs Sync | How microservices communicate with each other
image credit: stackademic.com

HTTP-based Asynchronous Communication

Just from the name “Asynchronous” you might have guessed it right? This type of HTTP calls are made but we don’t wait for the response. Response can come at a later time which allows us to create non-blocking interactions.

Advantages:

  1. Resilience and Scalability: As asynchronous connections, don’t wait for the response and just move on to the next part, it provides a resilient system by making the systems more decoupled and independent! Having a higher degree of independence, scaling up in such systems becomes very easy! 
  2. Loose Coupling: By making the systems functionally independent, you end up getting a very loosely coupled and isolated system which is good!
  3. Event-Driven Architecture: Asynchronous communication facilitates one of the modern software architecture patterns event-driven architecture. In this pattern, one publishes events and other services subscribes or listens to events published, and acts accordingly.

Disadvantages

  1. Complexity: Adding asynchronous communication to the system, makes tracking of message passing complex and, may get hard later. From my past experiences, my suggestion would be, that you should go for reliable messaging brokers like Kafka or RabbutMQ, etc.
  2. Debugging and Monitoring: As I said tracking the issues may get super hard if not managed properly! To ensure reliable message delivery you needed to have proper documentation and a preplanning mechanism for how to reply to any past event. Because my friend trust me, you will be in situations where you need to retrigger a past event.
  3. Error Handling: Handling errors in your code is a must-have thing! The problem with asynchronous communication is the responses we get or the action does not take place instantly. This makes it harder to investigate the issue.

gRPC: Revolutionizing Synchronous Protocols

gRPC is a high-performance RPC (Remote Procedure Call) framework by Google. It allows microservices to communicate synchronously and in a bi-directional manner. gRPC has gained significant attention due to its significant benefits to the microservices.

gPRC | How microservices communicate with each other
image credit: token.io

Advantages

  1. Efficiency: gRPC is essentially designed for low latency and high throughput communications. This makes it ideal for lightweight systems where efficiency is the priority.
  2. Polyglot Nature: It allows the microservices to run on different technologies. In this way, services are not forced to use some specific technology to have gRPC. 
  3. Real-time Communication: gPRC provides bi-directional streaming and real-time communication between the microservices.
  4. Language-agnostic Service Contract: In gRPC, a Language-agnostic Service Contract is like a universal translator for microservices. It defines how they communicate, no matter their programming language, thanks to Protocol Buffers that generate code for everyone, leading to efficient and clear collaboration across software kingdoms.

Message Queues: Asynchronous Harmony

Similar to asynchronous HTTP calls, in message queues, we generate the data, and put it in a message queue for processing! Now it is the responsibility of the queue to keep the data and pass it on to the intended service!

Services like RabbitMQ, Azure Service Bus, Kafka, etc, are widely adopted systems you can use as message queues for your system. With message queues, you need to keep in mind that such setups are meant for long-running systems not suitable for real-time communications.

Publish/Subscribe (Pub/Sub) Model

Pub/Sub model working on the events published and reacting to published events by subscribing to them. Think of it like a town crier shouting “New order!”. Publishers “publish” messages to topics, and subscribers interested in that topic get notified. Any specific action is up to the subscriber.

In short, it broadcasts real-time messages on topics. Focus on message delivery.

Pub/Sub Model | How microservices communicate with each other
image credit: twitter.com (by @NikkiSiapno)

Event-driven Communication: Dynamic Interactions

It is similar to the Pub/Sub Model, but it reacts to specific events that have already happened. Think of it like a news headline: “Order shipped!”. Microservices subscribe to specific events and take action accordingly. The focus is on the event itself, not who sent it or what to do next.

In short, it reacts to past events. Focus on event details

  1. Semantic APIs: Just beyond normal data formats, if the APIs become semantically rich like adding context and intent in the messages. It would allow much more meaningful and will reduce ambiguity between services. Imagine an API not just sending “order completed,” but “order #123 shipped, ETA 5pm.”
  2. AI-powered Coordination: Artificial intelligence can play a big role in optimizing the responses based on communication patterns. Think of AI agents negotiating load balancing and dynamically reconfiguring service chains based on real-time needs.
  3. Edge-focused Communication: These days, edge computing is at its boom. If microservices can communicate to such edge devices and get the data bypassing the central hub would be amazing. We can reduce latency in cases of geographically distributed applications. Imagine smart sensors talking directly to local microservices instead of going through a central cloud server.
  4. Security at the Forefront: As communication complexity increases, securing microservices interactions becomes paramount. Expect stronger encryption, zero-trust architectures, and intrusion detection systems built specifically for distributed systems.

The main motto of such future communication is to make these interactions smarter, faster, and more reliable right?

And remember these are my thoughts. The future is always surprising. But I believe these thoughts will give you some food for your brain which thinks out of the box. Who knows, maybe you are the one who will bring a new communication technique to the world.

Conclusion

So, in this article, we saw some of the solutions and some futuristic possibilities that answer how microservices communicate with each other.  From HTTP requests to event-driven communication, we saw the harmony of data between the services. 

Let me know in the comment section below if you know any other ways, that I missed here, or anything that you want to add to it. Share your experiences with us! We learn together!

References:

FAQs

  1. How do microservices synchronize their communication?

    Microservices achieve synchronization through HTTP-based synchronous communication, utilizing standard HTTP methods for direct interactions.

  2. Can microservices communicate without real-time constraints?

    Absolutely! HTTP-based asynchronous communication enables microservices to interact without being bound by real-time constraints. Requests are sent, and responses are received at a later time.

  3. What sets gRPC apart in microservices communication?

    gRPC, developed by Google, introduces a high-performance, open-source RPC framework. It revolutionizes microservices communication with a synchronous protocol.

  4. How do message queues enhance microservices communication?

    Message queues like RabbitMQ and Azure Service Bus are crucial in asynchronous communication. Services send messages to queues; others consume them when ready.

  5. What makes Pub/Sub an enticing communication style for microservices?

    Pub/Sub allows microservices to publish events, and subscribing services receive updates. It’s a dynamic broadcasting model that enhances communication efficiency.

  6. How do microservices engage in event-driven communication?

    Microservices communicate by exchanging events triggered by state changes. This dynamic interaction adds agility and responsiveness to the microservices architecture.

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