Request and response mapping in AWS - Step-by-Step Execution

Process Flow - Request and response mapping

Client sends request

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API Gateway receives request

↓

Request Mapping Template applies

↓

Mapped request sent to backend

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Backend processes request

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Backend sends response

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Response Mapping Template applies

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Mapped response sent to client

The client sends a request that API Gateway receives. It applies a request mapping template to transform the request before sending it to the backend. After the backend processes it and sends a response, API Gateway applies a response mapping template to transform the response before sending it back to the client.

Execution Sample

AWS

POST /items HTTP/1.1
Host: api.example.com
Content-Type: application/json

{"name":"apple","qty":10}

Client sends a POST request with JSON data to API Gateway, which will map the request and response.

Process Table

Step	Action	Input	Output	Notes
1	Receive client request	{"name":"apple","qty":10}	Raw request data	API Gateway gets the original request
2	Apply request mapping	Raw request data	{"itemName":"apple","quantity":10}	Transforms JSON keys to backend format
3	Send mapped request to backend	{"itemName":"apple","quantity":10}	Mapped request sent	Backend receives transformed data
4	Backend processes request	{"itemName":"apple","quantity":10}	{"status":"success","id":123}	Backend creates item and returns response
5	Apply response mapping	{"status":"success","id":123}	{"result":"Item created","itemId":123}	Transforms backend response to client format
6	Send mapped response to client	{"result":"Item created","itemId":123}	Final response to client	Client receives transformed response
7	End	N/A	N/A	Request-response cycle complete

💡 Request and response mapping complete; client receives final transformed response.

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
RequestPayload	{"name":"apple","qty":10}	{"itemName":"apple","quantity":10}	{"itemName":"apple","quantity":10}	{"itemName":"apple","quantity":10}	Sent to backend
ResponsePayload	N/A	N/A	{"status":"success","id":123}	{"result":"Item created","itemId":123}	Sent to client

Key Moments - 3 Insights

Why do we need to transform the request before sending it to the backend?

Because the backend expects data in a specific format different from the client’s. The request mapping template changes the client’s data to match backend requirements, as shown in step 2 of the execution_table.

What happens if the response mapping template is missing or incorrect?

The client might receive data in an unexpected format, causing confusion or errors. Step 5 shows how the response is transformed to the client’s expected format.

Does the original client request get changed?

No, the original request stays the same. API Gateway creates a transformed copy for the backend, as seen in variable_tracker where RequestPayload changes after step 2 but original client data is preserved.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after applying the request mapping template (Step 2)?

A {"name":"apple","qty":10}

B {"itemName":"apple","quantity":10}

C {"status":"success","id":123}

D {"result":"Item created","itemId":123}

💡 Hint

Check the Output column at Step 2 in the execution_table.

At which step does the backend send its response?

A Step 3

B Step 5

C Step 4

D Step 6

💡 Hint

Look for the step where backend processes and returns data in the execution_table.

If the response mapping template was removed, what would the client receive?

A The backend response without transformation

B The original client request

C An error message from API Gateway

D An empty response

💡 Hint

Refer to the role of response mapping in Step 5 and 6 in the execution_table.

Concept Snapshot

Request and response mapping in API Gateway:
- Client sends request
- Request mapping template transforms request
- Backend receives transformed request
- Backend sends response
- Response mapping template transforms response
- Client receives transformed response
Mapping ensures backend and client understand each other.

Full Transcript

In request and response mapping, the client sends a request to API Gateway. API Gateway applies a request mapping template to change the request format to what the backend expects. The backend processes this transformed request and sends back a response. API Gateway then applies a response mapping template to change the backend response into a format the client expects. Finally, the client receives this transformed response. This process ensures smooth communication between client and backend even if they use different data formats.