How to Stop PHPSESSID Changing with AWS Lambda/CloudFront?

Are you tired of dealing with the pesky PHPSESSID changes when using AWS Lambda and CloudFront? Well, you’re in luck! In this article, we’ll dive into the world of serverless architecture and CDN magic to show you exactly how to stop PHPSESSID from changing and keep your session management in check.

What’s the Problem?

When you use AWS Lambda and CloudFront, each Lambda function invocation generates a new PHPSESSID. This can lead to issues with session management, as the PHPSESSID is changed with each request. This can be frustrating, especially when you’re trying to maintain a seamless user experience.

Why Does PHPSESSID Change?

The reason PHPSESSID changes with each Lambda invocation is due to the serverless nature of Lambda functions. Each function invocation is a new, isolated execution environment, and PHPSESSID is generated anew with each request. CloudFront, as a CDN, further complicates the issue by caching responses and potentially serving stale PHPSESSID values.

Understanding the Solution

To stop PHPSESSID from changing, we need to ensure that PHPSESSID is generated and stored consistently across all Lambda function invocations and CloudFront cache invalidations. We’ll achieve this by implementing a custom session management strategy using AWS services.

Step 1: Configure Lambda Function to Use Custom Session Management

In your Lambda function, add the following code to initialize a custom session management system:

<?php
session_set_save_handler(new CustomSessionHandler());
session_start();
?>

This code sets up a custom session handler, which we’ll implement in the next step.

Step 2: Implement Custom Session Handler

Create a new PHP class, `CustomSessionHandler`, which will handle session storage and retrieval:

<?php
class CustomSessionHandler implements SessionHandlerInterface {
    private $tableName = 'sessions';

    public function open($savePath, $name) {
        // Initialize DynamoDB client
        $dynamodb = new Aws\DynamoDb\DynamoDbClient([
            'version' => 'latest',
            'region' => 'your-region',
        ]);

        // Create DynamoDB table if it doesn't exist
        $dynamodb->createTable([
            'TableName' => $this->tableName,
            'AttributeDefinitions' => [
                [
                    'AttributeName' => 'id',
                    'AttributeType' => 'S',
                ],
                [
                    'AttributeName' => 'data',
                    'AttributeType' => 'S',
                ],
            ],
            'KeySchema' => [
                [
                    'AttributeName' => 'id',
                    'KeyType' => 'HASH',
                ],
            ],
            'TableStatus' => 'ACTIVE',
        ]);

        return true;
    }

    public function close() {
        return true;
    }

    public function read($id) {
        // Retrieve session data from DynamoDB
        $result = $dynamodb->getItem([
            'TableName' => $this->tableName,
            'Key' => [
                'id' => [
                    'S' => $id,
                ],
            ],
        ]);

        return $result->get('Item')->get('data')->get('S');
    }

    public function write($id, $data) {
        // Store session data in DynamoDB
        $dynamodb->putItem([
            'TableName' => $this->tableName,
            'Item' => [
                'id' => [
                    'S' => $id,
                ],
                'data' => [
                    'S' => $data,
                ],
            ],
        ]);

        return true;
    }

    public function destroy($id) {
        // Delete session data from DynamoDB
        $dynamodb->deleteItem([
            'TableName' => $this->tableName,
            'Key' => [
                'id' => [
                    'S' => $id,
                ],
            ],
        ]);

        return true;
    }

    public function gc($lifetime) {
        // Implement garbage collection logic
        // ...
    }
}
?>

This custom session handler uses Amazon DynamoDB to store session data. It provides the necessary methods for reading, writing, and destroying session data, as well as garbage collection.

Step 3: Configure CloudFront to Invalidate Cache

To ensure that CloudFront cache is invalidated when the PHPSESSID changes, add a Lambda edge function to your CloudFront distribution:

exports.handler = async (event) => {
    // Invalidate CloudFront cache
    const cf = new AWS.CloudFront({ region: 'your-region' });
    const distributionId = 'your-distribution-id';
    const cacheId = 'your-cache-id';

    cf.createInvalidation({
        DistributionId: distributionId,
        InvalidationBatch: {
            CallerReference: Date.now().toString(),
            List: ['/*'],
        },
    }).promise();

    return {
        statusCode: 200,
    };
};

This Lambda edge function invalidates the CloudFront cache whenever it’s invoked, ensuring that the latest PHPSESSID is served to users.

Solution in Action

Now that we’ve implemented the custom session management system, let’s see how it works:

Step	Description
1	User requests a page, and Lambda function is invoked.
2	Custom session handler is initialized, and PHPSESSID is generated.
3	Session data is stored in DynamoDB.
4	User requests another page, and Lambda function is invoked again.
5	Custom session handler retrieves PHPSESSID from DynamoDB.
6	Session data is retrieved from DynamoDB using the stored PHPSESSID.
7	CloudFront cache is invalidated using the Lambda edge function.
8	User receives the updated PHPSESSID, and the session is maintained.

By using this custom session management system, we’ve successfully stopped PHPSESSID from changing with each Lambda function invocation and CloudFront cache invalidation.

Benefits and Considerations

By implementing this solution, you’ll enjoy the following benefits:

• Consistent PHPSESSID across Lambda function invocations and CloudFront cache invalidations.
• Improved session management and user experience.
• Scalability and high availability using AWS Lambda and CloudFront.

However, keep in mind the following considerations:

• Additional complexity in implementing and managing the custom session handler and DynamoDB table.
• Potential increased costs due to DynamoDB storage and Lambda function invocations.
• Importance of implementing robust error handling and logging mechanisms to ensure reliable operation.

In conclusion, by following these steps and implementing a custom session management system, you can stop PHPSESSID from changing with each Lambda function invocation and CloudFront cache invalidation, ensuring a seamless user experience and smooth operation of your application.

Frequently Asked Question

Got stuck with PHPSESSID changing issues on AWS Lambda/CloudFront? Worry not, we’ve got you covered!