To get started with Lambda, use the Lambda console to create a function. In a few minutes, you can create and deploy a function and test it in the console.

As you carry out the tutorial, you'll learn some fundamental Lambda concepts, like how to pass arguments to your function using the Lambdaevent object. You'll also learn how to return log outputs from your function, and how to view your function's invocation logs in Amazon CloudWatch Logs.

To keep things simple, you create your function using either the Python or Node.js runtime. With these interpreted languages, you can edit function code directly in the console's built-in code editor. With compiled languages like Java and C#, you must create a deployment package on your local build machine and upload it to Lambda. To learn about deploying functions to Lambda using other runtimes, see the links in theAdditional resources and next steps section.

Prerequisites

Create a Lambda function with the console

In this example, your function takes a JSON object containing two integer values labeled"length" and"width". The function multiplies these values to calculate an area and returns this as a JSON string.

Your function also prints the calculated area, along with the name of its CloudWatch log group. Later in the tutorial, you’ll learn to useCloudWatch Logs to view records of your functions’ invocation.

In addition to a simple function that returns the messageHello from Lambda!, Lambda also creates anexecution role for your function. An execution role is an AWS Identity and Access Management (IAM) role that grants a Lambda function permission to access AWS services and resources. For your function, the role that Lambda creates grants basic permissions to write to CloudWatch Logs.

Use the console's built-in code editor to replace the Hello world code that Lambda created with your own function code.

Node.js

To modify the code in the console

1. Choose theCode tab.

   In the console's built-in code editor, you should see the function code that Lambda created. If you don't see theindex.mjs tab in the code editor, selectindex.mjs in the file explorer as shown on the following diagram.

   

2. Paste the following code into theindex.mjs tab, replacing the code that Lambda created.

   export const handler = async (event, context) =>{    const length = event.length;  const width = event.width;  let area = calculateArea(length, width);  console.log(`The area is ${area}`);          console.log('CloudWatch log group: ', context.logGroupName);    let data ={    "area": area,  };    return JSON.stringify(data);      function calculateArea(length, width){    return length * width;  }};

3. In theDEPLOY section, chooseDeploy to update your function's code:

   

Understanding your function code

Before you move to the next step, let's take a moment to look at the function code and understand some key Lambda concepts.

• The Lambda handler:

  Your Lambda function contains a Node.js function namedhandler. A Lambda function in Node.js can contain more than one Node.js function, but thehandler function is always the entry point to your code. When your function is invoked, Lambda runs this method.

  When you created your Hello world function using the console, Lambda automatically set the name of the handler method for your function tohandler. Be sure not to edit the name of this Node.js function. If you do, Lambda won’t be able to run your code when you invoke your function.

  To learn more about the Lambda handler in Node.js, seeDefine Lambda function handler in Node.js.

• The Lambda event object:

  The functionhandler takes two arguments,event andcontext. Anevent in Lambda is a JSON formatted document that contains data for your function to process.

  If your function is invoked by another AWS service, the event object contains information about the event that caused the invocation. For example, if your function is invoked when an object is uploaded to an Amazon Simple Storage Service (Amazon S3) bucket, the event contains the name of the bucket and the object key.

  In this example, you’ll create an event in the console by entering a JSON formatted document with two key-value pairs.

• The Lambda context object:

  The second argument that your function takes iscontext. Lambda passes thecontext object to your function automatically. The context object contains information about the function invocation and execution environment.

  You can use the context object to output information about your function's invocation for monitoring purposes. In this example, your function uses thelogGroupName parameter to output the name of its CloudWatch log group.

  To learn more about the Lambda context object in Node.js, seeUsing the Lambda context object to retrieve Node.js function information.

• Logging in Lambda:

  With Node.js, you can use console methods likeconsole.log andconsole.error to send information to your function's log. The example code usesconsole.log statements to output the calculated area and the name of the function's CloudWatch Logs group. You can also use any logging library that writes tostdout orstderr.

  To learn more, seeLog and monitor Node.js Lambda functions. To learn about logging in other runtimes, see the 'Building with' pages for the runtimes you're interested in.

Python

To modify the code in the console

1. Choose theCode tab.

   In the console's built-in code editor, you should see the function code that Lambda created. If you don't see thelambda_function.py tab in the code editor, selectlambda_function.py in the file explorer as shown on the following diagram.

   

2. Paste the following code into thelambda_function.py tab, replacing the code that Lambda created.

   import jsonimport logginglogger = logging.getLogger()logger.setLevel(logging.INFO)def lambda_handler(event, context):        # Get the length and width parameters from the event object. The     # runtime converts the event object to a Python dictionary    length = event['length']    width = event['width']        area = calculate_area(length, width)    print(f"The area is{area}")            logger.info(f"CloudWatch logs group:{context.log_group_name}")        # return the calculated area as a JSON string    data ={"area": area}    return json.dumps(data)    def calculate_area(length, width):    return length*width

3. In theDEPLOY section, chooseDeploy to update your function's code:

   

Understanding your function code

Before you move to the next step, let's take a moment to look at the function code and understand some key Lambda concepts.

• The Lambda handler:

  Your Lambda function contains a Python function namedlambda_handler. A Lambda function in Python can contain more than one Python function, but thehandler function is always the entry point to your code. When your function is invoked, Lambda runs this method.

  When you created your Hello world function using the console, Lambda automatically set the name of the handler method for your function tolambda_handler. Be sure not to edit the name of this Python function. If you do, Lambda won’t be able to run your code when you invoke your function.

  To learn more about the Lambda handler in Python, seeDefine Lambda function handler in Python.

• The Lambda event object:

  The functionlambda_handler takes two arguments,event andcontext. Anevent in Lambda is a JSON formatted document that contains data for your function to process.

  If your function is invoked by another AWS service, the event object contains information about the event that caused the invocation. For example, if your function is invoked when an object is uploaded to an Amazon Simple Storage Service (Amazon S3) bucket, the event contains the name of the bucket and the object key.

  In this example, you’ll create an event in the console by entering a JSON formatted document with two key-value pairs.

• The Lambda context object:

  The second argument that your function takes iscontext. Lambda passes thecontext object to your function automatically. The context object contains information about the function invocation and execution environment.

  You can use the context object to output information about your function's invocation for monitoring purposes. In this example, your function uses thelog_group_name parameter to output the name of its CloudWatch log group.

  To learn more about the Lambda context object in Python, seeUsing the Lambda context object to retrieve Python function information.

• Logging in Lambda:

  With Python, you can use either aprint statement or a Python logging library to send information to your function's log. To illustrate the difference in what's captured, the example code uses both methods. In a production application, we recommend that you use a logging library.

  To learn more, seeLog and monitor Python Lambda functions. To learn about logging in other runtimes, see the 'Building with' pages for the runtimes you're interested in.

Invoke the Lambda function using the console code editor

To invoke your function using the Lambda console code editor, create a test event to send to your function. The event is a JSON formatted document containing two key-value pairs with the keys"length" and"width".

To test your function and view invocation records

In theTEST EVENTS section of the console code editor, choose the run icon next to your test event:

When your function finishes running, the response and function logs are displayed in theOUTPUT tab. You should see results similar to the following:

Clean up

When you're finished working with the example function, delete it. You can also delete the log group that stores the function's logs, and theexecution role that the console created.

Additional resources and next steps

Now that you’ve created and tested a simple Lambda function using the console, take these next steps:

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