After you migrate the application, you can run a page speed insight tool to measure this application’s performance. This tool provides results mostly about the front end and the experience that the user perceives. The results are displayed in the following image. The performance of this website is good, according to the insight tool performance score - it responds quickly and the user experience is good.

After the application is migrated to a serverless environment, you can do some refactoring to improve further the overall performance. One alternative is whenever a new image is uploaded, it gets resized and formatted into the correct next-gen format automatically using the event driven capabilities that S3 provides. Another alternative is to use Lambda@Edge to serve the right image size for the device, as it is possible to format the images on the fly when serving them from a distribution.

You can run load tests for understanding how your backend and database will perform. For this, you can use Artillery, an open-source library that allows you to run load tests. You can run tests with the expected maximum load your site will get and ensure that your site can handle it.

For example, you can configure a test that sends 30 requests per seconds to see how your application reacts:

config:
  target: 'https://xxx.lambda-url.eu-west-1.on.aws'
  phases:
    - duration: 240
      arrivalRate: 30
      name: Testing
scenarios:
  - name: 'Test main page'
    flow:
      - post:
          url: '/api/product/getProducts/'

Check this video at the top to run these tests.

This test is performed on the backend APIs, not only testing your backend but also your integration with the MongoDB. After running it, you can see how the Lambda function performs on the Amazon CloudWatch dashboard.

This video explains how to create this dashboard.

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Running this load test helps you understand the limitations of your system. For example, if you run a test with too many concurrent users, you might see that the number of throttles in your function increases. This means that you need to lift the limit of your functions' concurrent invocations (how many invocations you can have at the same time).

Or when increasing the requests per second, you may find that the MongoDB cluster starts throttling your requests. This is because you are using the free tier which has a set number of connections. You might need a larger cluster or to migrate your database to another service that provides a large free tier, like Amazon DynamoDB.