Lambda integration in AWS - Step-by-Step Execution

Process Flow - Lambda integration

Client Request

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API Gateway receives request

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API Gateway triggers Lambda function

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Lambda function executes code

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Lambda returns response

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API Gateway sends response to client

This flow shows how a client request goes through API Gateway to trigger a Lambda function, which processes and returns a response back to the client.

Execution Sample

AWS

1. Client sends HTTP request to API Gateway
2. API Gateway triggers Lambda function
3. Lambda runs code and returns result
4. API Gateway sends response to client

This sequence shows the steps of Lambda integration with API Gateway handling a client request.

Process Table

Step	Component	Action	Input	Output
1	Client	Sends HTTP request	GET /hello	Request sent to API Gateway
2	API Gateway	Receives request	GET /hello	Triggers Lambda function
3	Lambda	Executes function code	Event with request data	Returns response payload
4	API Gateway	Receives Lambda response	Response payload	Sends HTTP response to client
5	Client	Receives response	HTTP 200 OK with message	Displays response

💡 Execution stops after client receives the response from API Gateway.

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Request	None	HTTP GET /hello	Event passed to Lambda	Response payload from Lambda	HTTP 200 OK response
Response	None	None	Lambda response generated	API Gateway response ready	Displayed to client

Key Moments - 3 Insights

Why does API Gateway trigger the Lambda function instead of the client calling Lambda directly?

API Gateway acts as a secure front door that accepts client requests and triggers Lambda. This allows managing access, routing, and protocols. See execution_table step 2.

What does the Lambda function receive as input?

Lambda receives an event object containing request details from API Gateway, not the raw HTTP request. See execution_table step 3.

How does the client get the Lambda function's response?

Lambda returns a response to API Gateway, which formats and sends it back to the client as an HTTP response. See execution_table steps 4 and 5.

Visual Quiz - 3 Questions

Look at the execution table, at which step does the Lambda function execute its code?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'Component' and 'Action' columns in execution_table row for step 3.

At which step does the client receive the HTTP response?

A Step 5

B Step 3

C Step 1

D Step 4

💡 Hint

Look for when the client 'Receives response' in the execution_table.

If the Lambda function fails to return a response, which step would be affected?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Consider when API Gateway 'Receives Lambda response' in execution_table step 4.

Concept Snapshot

Lambda integration with API Gateway:
- Client sends HTTP request to API Gateway
- API Gateway triggers Lambda function with event data
- Lambda executes code and returns response
- API Gateway sends HTTP response back to client
- Enables serverless backend for web APIs

Full Transcript

This visual execution shows how a client request flows through API Gateway to trigger a Lambda function. The client sends an HTTP request which API Gateway receives. API Gateway then triggers the Lambda function by passing an event object. The Lambda function runs its code and returns a response payload. API Gateway receives this response and sends it back to the client as an HTTP response. The client finally receives and displays the response. Key points include API Gateway acting as a secure front door, Lambda receiving event data, and the response flow back to the client.