[SOLVED] How do you pass a query string or route parameter to AWS Lambda from Amazon API Gateway? - amazon-web-services

[SOLVED] How to Pass Query Strings and Route Parameters to AWS Lambda via Amazon API Gateway

In this guide, we will learn how to pass query strings and route parameters from Amazon API Gateway to AWS Lambda. It is important for us to understand how API Gateway and Lambda work together. This will help us create strong serverless applications. We will cover the basic structure of API Gateway requests and practical setups. This way, we can make data flow into our Lambda functions easier.

In this chapter, we will talk about these solutions:

Understanding API Gateway Request Structure: We will learn the basics of how requests are made in API Gateway.
Configuring Query String Parameters in API Gateway: We will see how to set up query string parameters for our API.
Setting Up Route Parameters in API Gateway: We will find out how to set up route parameters correctly.
Mapping Query Strings to Lambda Function Input: We will learn how to connect query string parameters to our Lambda function’s input.
Testing Your API with Query String and Route Parameters: We will understand how to test our API to check if parameters are passed right.
Handling Parameters in AWS Lambda Function: We will see how to work with these parameters inside our Lambda functions.
Frequently Asked Questions: We will answer common questions about using API Gateway and Lambda together.

By following this guide, we will learn how to pass query strings and route parameters to AWS Lambda from Amazon API Gateway. We will also learn how to make this process better for performance and reliability. If we want to learn more about AWS, we can check our other tutorials. For example, you can look at how to configure access control or how to increase your Lambda function’s efficiency.

Part 1 - Understanding API Gateway Request Structure

To send a query string or route parameter to AWS Lambda from Amazon API Gateway, we need to know the request structure that API Gateway uses when it calls a Lambda function. The request from API Gateway to Lambda is a JSON object. This object has many properties.

Key Components of the API Gateway Request:

httpMethod: This is the HTTP method used like GET or POST.
path: This is the resource path we define in the API Gateway.
queryStringParameters: This is a map of key-value pairs for query string parameters.
pathParameters: This is a map of key-value pairs for any route parameters in the API.
headers: This is a map of request headers.
body: This is the data sent with the request. It is mainly for POST requests.

Example Request Structure:

{
  "httpMethod": "GET",
  "path": "/example/path",
  "queryStringParameters": {
    "param1": "value1",
    "param2": "value2"
  },
  "pathParameters": {
    "id": "12345"
  },
  "headers": {
    "Content-Type": "application/json"
  },
  "body": null
}

How This Relates to Lambda:

When API Gateway calls a Lambda function, it sends a request payload like the one above. Inside our Lambda function, we can get these parameters using the event object that the function receives.

Accessing Parameters in Lambda:

We can get the query string and route parameters like this:

def lambda_handler(event, context):
    query_params = event.get('queryStringParameters')
    path_params = event.get('pathParameters')

    param1_value = query_params.get('param1') if query_params else None
    id_value = path_params.get('id') if path_params else None

    return {
        'statusCode': 200,
        'body': f'Param1: {param1_value}, ID: {id_value}'
    }

Understanding the API Gateway request structure is very important for sending query strings and route parameters to AWS Lambda. For more information on how we can configure our API Gateway, check this guide on query string parameters.

Part 2 - Configuring Query String Parameters in API Gateway

To send query string parameters from Amazon API Gateway to an AWS Lambda function, we need to set up our API Gateway. It should recognize and pass these parameters. Here is how we can do this:

Open the API Gateway Console:
- Go to the API Gateway console in the AWS Management Console.
Select Your API:
- Pick the API we want to set up.
Choose a Resource:
- Select the resource, like /items, where we want to add query string parameters.
Create or Select a Method:
- We can create a new method (GET, POST, etc.) or choose one that is already there.
Enable Query String Parameters:
- In the method settings, find the Method Request part.
- Open the URL Query String Parameters section.
- Click on Add query string and write the name of the parameter (like itemId).
- We can also make it required if we want.
Map Query Strings to Lambda Input:
- In the Integration Request part, we will link the query string parameter to our Lambda function input.
- Under Mapping Templates, choose When there are no templates defined (recommended).
- Add a mapping template for the content type (like application/json):
```
{
  "itemId": "$input.params('itemId')"
}
```
Deploy the API:
- After we finish the setup, we need to deploy the API to apply the changes.

Example of a query string in a request URL:

https://api-id.execute-api.region.amazonaws.com/prod/items?itemId=123

The Lambda function will get the query string parameter in the event object. For example, we can access it in the Lambda function like this:

def lambda_handler(event, context):
    item_id = event['queryStringParameters']['itemId']
    # Process the itemId as needed

Now, our AWS Lambda function can get the query string parameters from Amazon API Gateway. For more details on how to handle parameters, see how can AWS Lambda function input.

Part 3 - Setting Up Route Parameters in API Gateway

To send route parameters to AWS Lambda using Amazon API Gateway, we must set up the API Gateway to understand these parameters in the URL path. Here are the steps to set up route parameters easily:

Create or choose an API in the AWS API Gateway console.
Define a Resource:
- Click on “Resources” in your API.
- Choose “Create Resource”.
- Enter a Resource Name and set the Resource Path with the parameter. For example, use /users/{userId} where {userId} is the route parameter.
Create a Method:
- Select the resource we just made.
- Click “Create Method” and pick an HTTP method like GET.
- For integration type, choose “Lambda Function” and enter your Lambda function name.
Enable CORS if needed by clicking on “Enable CORS” in the Method settings.
Deploy the API:
- Click on “Actions” and choose “Deploy API”.
- Pick a Deployment stage or make a new one.

In our Lambda function, we can get the route parameters from the event object. Here is an example of how to get the userId parameter:

def lambda_handler(event, context):
    user_id = event["pathParameters"]["userId"]
    return {
        "statusCode": 200,
        "body": f"User ID received: {user_id}"
    }

Now when we make a request to /users/123, the Lambda function will get 123 as the userId.

For more details on how to handle query strings, please check how to pass a query string or route parameter to AWS Lambda.

Part 4 - Mapping Query Strings to Lambda Function Input

To pass query strings from Amazon API Gateway to AWS Lambda, we need to set up the mapping templates correctly. This step makes sure that the query string parameters go to our Lambda function as input.

Navigate to API Gateway Console:
- We select our API and go to the Resources section.
Select the Method:
- We choose the HTTP method like GET or POST that we want to set up for query string mapping.
Enable Query String Parameters:
- In the Method Request settings, we add the necessary query string parameters. For example, if we have a parameter called userId, we add it here.
Set Up Integration Request:
- We go to Integration Request and scroll down to the Mapping Templates section.
- We click on Add mapping template.
- We specify the content type, like application/json, and click on the checkmark.
Define the Mapping Template:
- In the template editor, we can map the query string parameters to the request body. Here is an example of how to do it:
```
{
  "userId": "$input.params('userId')",
  "otherParam": "$input.params('otherParam')"
}
```
Save Changes:
- After we define the mapping template, we click on Save.
Test the Integration:
- We use the Test feature in API Gateway to check if the query strings are passed correctly to our Lambda function.

Once we finish this setup, our AWS Lambda function will get the parameters as part of the event object. We can access them in our Lambda function like this:

def lambda_handler(event, context):
    user_id = event['userId']
    other_param = event.get('otherParam', None)

    # Your logic here

By following these steps, we can map query strings to our Lambda function input. This makes our AWS API Gateway integration smooth. For more details on managing AWS Lambda input, we can check this guide on how can AWS Lambda function input be managed.

Part 5 - Testing Your API with Query String and Route Parameters

We can test our API with query string and route parameters in AWS API Gateway. We can use tools like Postman or cURL. This helps us to send requests and check if our API works well with the parameters that go to the AWS Lambda function.

Using Postman

Create a New Request:
- Open Postman and make a new request.
- Choose the HTTP method like GET or POST based on what our API needs.
Set the Request URL:
- Type the API Gateway endpoint URL, like https://your-api-id.execute-api.region.amazonaws.com/stage/resource.
Add Query String Parameters:
- Click on the Params tab.
- Add key-value pairs for our query parameters:
  - Key: parameter1, Value: value1
  - Key: parameter2, Value: value2
Add Route Parameters (if needed):
- Change the URL to add route parameters, like https://your-api-id.execute-api.region.amazonaws.com/stage/resource/value1.
Send the Request:
- Click on the Send button to run the request.
- Check the response from the AWS Lambda function.

Using cURL

We can also test our API using cURL in the command line. Here is how we do it:

GET Request with Query String Parameters:

curl -X GET "https://your-api-id.execute-api.region.amazonaws.com/stage/resource?parameter1=value1&parameter2=value2"

GET Request with Route Parameters:

curl -X GET "https://your-api-id.execute-api.region.amazonaws.com/stage/resource/value1"

Verify Responses

We need to check the response to see if the Lambda function handles the parameters correctly. The response should show the input values that we sent through the query string or route parameters. We can also check the outputs against what we expect from our Lambda function.

For more information on how to pass a query string or route parameter to AWS Lambda from API Gateway, we can look at this link how to pass a query string or route parameter to AWS Lambda from API Gateway.

Part 6 - Handling Parameters in AWS Lambda Function

We will learn how to handle query strings and route parameters in our AWS Lambda function. We need to access the event object that the API Gateway gives us. This object has all the request data, including parameters.

Accessing Query String Parameters

We can get query string parameters from the queryStringParameters property of the event object. Here is how we do it:

exports.handler = async (event) => {
  const queryParams = event.queryStringParameters;

  if (queryParams) {
    const param1 = queryParams.param1; // Example query parameter
    console.log("Query Parameter:", param1);
  }

  // Our logic here
  return {
    statusCode: 200,
    body: JSON.stringify({ message: "Success", param1 }),
  };
};

Accessing Route Parameters

We can find route parameters in the pathParameters property of the event object. Here is an example:

exports.handler = async (event) => {
  const pathParams = event.pathParameters;

  if (pathParams) {
    const routeParam = pathParams.id; // Example route parameter
    console.log("Route Parameter:", routeParam);
  }

  // Our logic here
  return {
    statusCode: 200,
    body: JSON.stringify({ message: "Success", routeParam }),
  };
};

Example of Combined Handling

We can handle both types of parameters in one Lambda function:

exports.handler = async (event) => {
  const queryParams = event.queryStringParameters;
  const pathParams = event.pathParameters;

  const param1 = queryParams ? queryParams.param1 : null;
  const routeParam = pathParams ? pathParams.id : null;

  console.log("Query Parameter:", param1);
  console.log("Route Parameter:", routeParam);

  return {
    statusCode: 200,
    body: JSON.stringify({ message: "Success", param1, routeParam }),
  };
};

Testing Your Lambda Function

We can test our Lambda function using the AWS Lambda console or by calling it through the API Gateway. We need to pass the parameters in the URL correctly. For example:

Query String: /your-api?param1=value1
Route Parameter: /your-api/value

For more information on handling AWS Lambda and API Gateway together, please check this guide.

Frequently Asked Questions

1. How do we pass query string parameters to AWS Lambda via API Gateway?

To pass query string parameters to AWS Lambda from Amazon API Gateway, we need to set up the API Gateway. We configure it to accept query strings in the resource method settings. This lets us extract the parameters and send them to our Lambda function. For detailed steps, we can check our guide on how to pass a query string or route parameter to AWS Lambda.

2. What are route parameters, and how do they differ from query string parameters?

Route parameters are part of the URL path. They help us identify specific resources. On the other hand, query string parameters are added to the URL. They give extra information. For example, /users/{userId} has a route parameter. But /users?age=25 has a query string. We can learn more about setting up route parameters in our article on how to pass a query string or route parameter to AWS Lambda.

3. Can we map query string parameters directly to Lambda function input?

Yes, we can map query string parameters directly to our AWS Lambda function’s input. We do this by setting up the mapping template in API Gateway. This makes the parameters available in our Lambda function. For more info on mapping query strings to Lambda, we can check our guide on how to pass a query string or route parameter to AWS Lambda.

4. How do we test our API with query string and route parameters?

To test our API with query string and route parameters, we can use tools like Postman or cURL. We just need to send a request to our API endpoint with the parameters in the URL. For step-by-step instructions, we can look at our section on how to pass a query string or route parameter to AWS Lambda.

5. What happens if our Lambda function doesn’t handle the parameters correctly?

If our AWS Lambda function does not handle the parameters right, it may give us errors or strange results. So it is important to check and process the input parameters correctly in our Lambda logic. For best tips on handling parameters in AWS Lambda, we can read our article on how to pass a query string or route parameter to AWS Lambda.

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