What is the difference between synchronous and asynchronous communication?

Question

Accepted Answer

**Synchronous** — caller waits. **Asynchronous** — caller doesn't wait.

**Synchronous:**
- Request-response pattern.
- Caller blocks until response.
- Simple, immediate feedback.
- Tightly coupled.

```
Synchronous (REST):
Client → Request → Server
Client ← Response ← Server
(Client waits for response)
```

**Asynchronous:**
- Message-based pattern.
- Caller continues immediately.
- Eventually consistent.
- Loosely coupled.

```
Asynchronous (Message Queue):
Producer → Message → Queue → Consumer
(Producer continues immediately)
```

**Use Cases:**
- **Sync** — user login, real-time queries.
- **Async** — email sending, order processing.

**Key differences:**
- **Sync** — wait for response.
- **Async** — fire and forget.

Systems Analyst: What is the difference between synchronous and asynchronous communication?