# Write and create a Lambda@Edge function
<a name="lambda-edge-create-function"></a>

To use Lambda@Edge, you *write* the code for your AWS Lambda function. To help you write Lambda@Edge functions, see the following resources:
+  [Lambda@Edge event structure](lambda-event-structure.md) – Understand the event structure to use with Lambda@Edge.
+ [Lambda@Edge example functions](lambda-examples.md) – Example functions, such as A/B testing and generating an HTTP redirect.

The programming model for using Node.js or Python with Lambda@Edge is the same as using Lambda in an AWS Region. For more information, see [Building Lambda functions with Node.js](https://docs.aws.amazon.com/lambda/latest/dg/lambda-nodejs.html) or [Building Lambda functions with Python](https://docs.aws.amazon.com/lambda/latest/dg/lambda-python.html) in the *AWS Lambda Developer Guide*.

In your Lambda@Edge function, include the `callback` parameter and return the applicable object for request or response events:
+ **Request events** – Include the `cf.request` object in the response.

  If you're generating a response, include the `cf.response` object in the response. For more information, see [Generate HTTP responses in request triggers](lambda-generating-http-responses.md#lambda-generating-http-responses-in-requests). 
+ **Response events** – Include the `cf.response` object in the response.

After you write your own code or use one of the examples, you then create the function in Lambda. To create a function or edit an existing one, see the following topics:

**Topics**
+ [

# Create a Lambda@Edge function
](lambda-edge-create-in-lambda-console.md)
+ [

# Edit a Lambda function
](lambda-edge-edit-function.md)

 After you create the function in Lambda, you set up Lambda to run the function based on specific CloudFront events, which are called *triggers*. For more information, see [Add triggers for a Lambda@Edge function](lambda-edge-add-triggers.md).

# Create a Lambda@Edge function
<a name="lambda-edge-create-in-lambda-console"></a>

To set up AWS Lambda to run Lambda functions that are based on CloudFront events, follow this procedure.<a name="lambda-edge-create-function-procedure"></a>

**To create a Lambda@Edge function**

1. Sign in to the AWS Management Console and open the AWS Lambda console at [https://console.aws.amazon.com/lambda/](https://console.aws.amazon.com/lambda/).

1. If you already have one or more Lambda functions, choose **Create function**.

   If you've don't have any functions, choose **Get Started Now**.

1. In the Region list at the top of the page, choose **US East (N. Virginia)**.

1. Create a function using your own code or create a function starting with a CloudFront blueprint.
   + To create a function using your own code, choose **Author from scratch**. 
   + To display a list of blueprints for CloudFront, enter **cloudfront** in the filter field, and then choose **Enter**.

     If you find a blueprint that you want to use, choose the name of the blueprint.

1. In the **Basic information** section, specify the following values:

   1. **Name** – Enter a name for your function.

   1. **Role** – To get started quickly, choose **Create new role from template(s)**. You can also choose **Choose an existing role** or **Create a custom role**, and then follow the prompts to complete the information for this section.

   1. **Role name** – Enter a name for the role.

   1. **Policy templates** – Choose **Basic Edge Lambda permissions**.

1. If you chose **Author from scratch** in step 4, skip to step 7.

   If you chose a blueprint in step 4, the **cloudfront** section lets you create one trigger, which associates this function with a cache in a CloudFront distribution and a CloudFront event. We recommend that you choose **Remove** at this point, so there isn't a trigger for the function when it's created. Then you can add triggers later. 
**Tip**  
We recommend that you test and debug the function before adding triggers. If you add a trigger now, the function will run as soon as you create the function and it finishes replicating to AWS locations around the world, and the corresponding distribution is deployed.

1. Choose **Create function**.

   Lambda creates two versions of your function: \$1LATEST and Version 1. You can edit only the \$1LATEST version, but the console initially displays Version 1.

1. To edit the function, choose **Version 1** near the top of the page, under the ARN for the function. Then, on the **Versions** tab, choose **\$1LATEST**. (If you left the function and then returned to it, the button label is **Qualifiers**.)

1. On the **Configuration** tab, choose the applicable **Code entry type**. Then follow the prompts to edit or upload your code.

1. For **Runtime**, choose the value based on your function's code.

1. In the **Tags** section, add any applicable tags.

1. Choose **Actions**, and then choose **Publish new version**.

1. Enter a description for the new version of the function.

1. Choose **Publish**.

1. Test and debug the function. For more information about testing in the Lambda console, see [ Invoke a Lambda function using the console](https://docs.aws.amazon.com/lambda/latest/dg/getting-started.html#get-started-invoke-manually) in the *AWS Lambda Developer Guide*.

1. When you're ready to have the function execute for CloudFront events, publish another version and edit the function to add triggers. For more information, see [Add triggers for a Lambda@Edge function](lambda-edge-add-triggers.md).

# Edit a Lambda function
<a name="lambda-edge-edit-function"></a>

After you create a Lambda@Edge function, you can use the Lambda console to edit it.

**Notes**  
The original version is labeled \$1LATEST.
You can edit only the \$1LATEST version.
Each time you edit the \$1LATEST version, you must publish a new numbered version.
You can't create triggers for \$1LATEST.
When you publish a new version of a function, Lambda doesn't automatically copy triggers from the previous version to the new version. You must reproduce the triggers for the new version. 
When you add a trigger for a CloudFront event to a function, if there's already a trigger for the same distribution, cache behavior, and event for an earlier version of the same function, Lambda deletes the trigger from the earlier version.
After you make updates to a CloudFront distribution, like adding triggers, you must wait for the changes to propagate to edge locations before the functions you've specified in the triggers will work.<a name="lambda-edge-edit-function-procedure"></a>

**To edit a Lambda function**

1. Sign in to the AWS Management Console and open the AWS Lambda console at [https://console.aws.amazon.com/lambda/](https://console.aws.amazon.com/lambda/).

1. In the Region list at the top of the page, choose **US East (N. Virginia)**.

1. In the list of functions, choose the name of the function.

   By default, the console displays the \$1LATEST version. You can view earlier versions (choose **Qualifiers**), but you can only edit \$1LATEST.

1. On the **Code** tab, for **Code entry type**, choose to edit the code in the browser, upload a .zip file, or upload a file from Amazon S3.

1. Choose either **Save** or **Save and test**.

1. Choose **Actions**, and choose **Publish new version**. 

1. In the **Publish new version from \$1LATEST** dialog box, enter a description of the new version. This description appears in the list of versions, along with an automatically generated version number. 

1. Choose **Publish**.

   The new version automatically becomes the latest version. The version number appears on the **Version** in the upper-left corner of the page.
**Note**  
If you haven't added triggers for your function yet, see [Add triggers for a Lambda@Edge function](lambda-edge-add-triggers.md). 

1. Choose the **Triggers** tab.

1. Choose **Add trigger**.

1. In the **Add trigger** dialog box, choose the dotted box, and then choose **CloudFront**.
**Note**  
If you've already created one or more triggers for a function, CloudFront is the default service.

1. Specify the following values to indicate when you want the Lambda function to execute.

   1. **Distribution ID **– Choose the ID of the distribution that you want to add the trigger to.

   1. **Cache behavior** – Choose the cache behavior that specifies the objects that you want to execute the function on.

   1. **CloudFront event** – Choose the CloudFront event that causes the function to execute.

   1. **Enable trigger and replicate** – Select this check box so Lambda replicates the function to AWS Regions globally.

1. Choose **Submit**.

1. To add more triggers for this function, repeat steps 10 through 13.

For more information about testing and debugging the function in the Lambda console, see [ Invoke a Lambda function using the console](https://docs.aws.amazon.com/lambda/latest/dg/getting-started.html#get-started-invoke-manually) in the *AWS Lambda Developer Guide*.

When you're ready to have the function execute for CloudFront events, publish another version and edit the function to add triggers. For more information, see [Add triggers for a Lambda@Edge function](lambda-edge-add-triggers.md).