Clear feedback
The caller knows whether the operation succeeded or failed before continuing.
MODULE 07 · SYSTEM ARCHITECTURE
Synchronous
Synchronous communication makes the caller wait for a response before it continues.
01
What is it?
A synchronous flow completes one interaction before the caller moves on. A client sends a request, the receiving service does the work, and the response comes back through the same interaction.
Simple definition:
Ask, wait, receive the answer, then continue.
02
Think of it like...
Think of calling a help desk. You stay on the call while the agent looks up the answer. The conversation is direct and easy to follow, but you are waiting while the agent works.
Caller sends request
Service works
Caller receives response
03
What does it do?
Synchronous communication gives the caller an immediate answer when the operation is quick and the result is needed now.
Simple control flow
Request and response are easy to trace in a small workflow.
Waiting cost
A slow dependency can increase latency or make the user wait.
Failure coupling
If the dependency is unavailable, the caller may also be blocked.
PM perspective: synchronous is often right for decisions the user needs immediately, such as validating a password or showing an available price.
04
Where is it used?
Use it for short operations where the caller needs a confirmed result before the next step.
Login
The product needs to know whether credentials are accepted before opening the account.
Price quote
The checkout needs the current price before showing the total.
Form validation
The interface needs a validation response before allowing the next step.
Payment decision
The product may need an authorization result before confirming an order.
05
Example
In a login flow, the client sends credentials to an authentication service and waits for a success or failure response. The response determines whether the user sees the account or an error.
Submit login
Check credentials
Success or failure
06
How it connects
Synchronous calls commonly use a request-response API. The caller owns the waiting time and usually receives a direct result from the service it called.
Caller
Starts the request and waits for the response.
Service
Performs the operation and returns a result.
07
Do Not Confuse
Synchronous vs event-driven
Synchronous follows a direct request-response interaction. Event-driven lets consumers react to a published fact.
Synchronous vs parallel
A caller can wait for one task even while other work runs in parallel elsewhere.
Synchronous vs immediate
A synchronous response can still be slow. It only means the caller waits for it.
Synchronous vs reliable
Waiting for a response does not guarantee success; timeouts and failures still need handling.
08
Topic Glossary
| ENGLISH TERM | 中文 | SIMPLE ENGLISH | 中文小白理解 |
|---|---|---|---|
| Synchronous | 同步 | The caller waits for a response before continuing. | 调用方要等回应后才能继续。 |
| Request | 请求 | A message asking a service to do something. | 请系统执行某件事的一条消息。 |
| Response | 响应 | The result returned after a request. | 系统处理请求后返回的结果。 |
| Latency | 延迟 | The time it takes to receive a result. | 从发出请求到收到结果所花的时间。 |
09
What to Remember
Synchronous communication is direct and easy to understand, but the waiting time and dependency failures are part of the product experience.
PM perspective: use synchronous calls when the user needs a result now, and define the timeout, retry, and fallback when the answer does not arrive.