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✅ Communication Patterns

🔄 Communication Patterns – Synchronous (REST/gRPC/GraphQL)

🚦 What is Synchronous Communication?

In synchronous communication, the caller waits for the response before continuing. It’s like making a phone call — you ask a question and wait for the answer.

🔧 Common Synchronous Communication Methods:

1. 🌐 REST (Representational State Transfer)

  • Uses HTTP and JSON
  • Simple and widely used
  • Based on resources (like /orders, /users)
  • Good for: Public APIs, CRUD operations

✅ Pros:

  • Easy to use
  • Readable URLs
  • Standard HTTP methods (GET, POST, PUT, DELETE)

❌ Cons:

  • Over-fetching or under-fetching of data
  • No built-in schema validation

2. ⚡ gRPC (Google Remote Procedure Call)

  • Uses HTTP/2 and Protobuf (binary format)
  • Fast and efficient
  • Based on methods, not resources
  • Good for: Internal microservice-to-microservice communication

✅ Pros:

  • Very fast (binary + HTTP/2)
  • Strongly typed contracts (Protobuf)
  • Bi-directional streaming supported

❌ Cons:

  • Harder to debug than REST
  • Browser support limited

3. 🔍 GraphQL

  • Query language for APIs
  • You ask for exactly the data you need
  • One endpoint for everything (/graphql)
  • Good for: Complex UIs and mobile apps

✅ Pros:

  • No over-fetching or under-fetching
  • Flexible queries
  • Strong typing (via schema)

❌ Cons:

  • More complex to implement
  • Performance tuning can be tricky

🧠 When to Use Synchronous Communication?

Use when:

  • Immediate response is required (e.g., UI interactions)
  • Request → Response pattern fits well
  • Services are closely connected

Avoid when:

  • High load may cause latency
  • You need loose coupling or retries → prefer asynchronous/event-driven

🔁 Communication Patterns – Asynchronous (Message Queues & Events)

⏳ What is Asynchronous Communication?

In asynchronous communication, the sender does not wait for a response. It’s like sending a message or email — the receiver can process it later, at their own pace.

🧰 Common Asynchronous Communication Methods:

1. 📬 Message Queues

  • Services send messages to a queue
  • Other services pick up messages and process them
  • Examples: Azure Service Bus, RabbitMQ, Amazon SQS

✅ Good for:

  • Decoupling services
  • Load buffering
  • Background processing

2. 📢 Events (Pub/Sub)

  • Services publish events to a topic or event bus
  • Other services subscribe and react to those events
  • Examples: Kafka, Azure Event Grid, AWS SNS/SQS

✅ Good for:

  • Event-driven systems
  • Broadcasting changes to many services (e.g., "OrderPlaced" triggers shipping, email)

🎯 Benefits of Asynchronous Communication

Feature Benefit
🧩 Loose Coupling Services don’t depend on each other’s availability
🕒 Improved Resilience Temporary failures don’t break the flow
⚖️ Scalability Queues handle high load by buffering requests
⏱️ Non-blocking Fast response for sender (fire-and-forget)

❗ Challenges

  • Eventual consistency: Responses aren’t immediate
  • Harder to debug: No direct trace like REST calls
  • Message duplication or loss: Requires retry and idempotency logic
  • Delivery guarantees: At-least-once, at-most-once, exactly-once

🧠 When to Use Asynchronous Communication?

Use when:

  • Tasks can run in the background
  • You need decoupled services
  • Services should react to events (e.g., OrderPlaced → SendInvoice)

Avoid when:

  • Immediate feedback is needed (e.g., form submission UI)
  • Too many events make flow hard to track