How does serverless integrate with existing applications?

Serverless integration with existing applications typically involves offloading specific tasks or components to cloud functions or services while keeping core systems intact. This approach allows developers to modernize parts of an application without rewriting the entire codebase. For example, an existing monolithic application could use serverless functions for tasks like image processing, authentication, or background jobs. These functions are triggered by events (e.g., HTTP requests, file uploads, or database changes) and communicate with the main application via APIs or messaging queues. This reduces the need to scale or refactor the entire system while adding flexibility for new features.

A practical example is integrating AWS Lambda with a legacy web application. Suppose the application handles user-uploaded images but struggles with scaling during peak traffic. By moving image resizing or compression to Lambda, the main server no longer needs to manage those resource-heavy tasks. When a user uploads an image, the application stores it in a cloud storage service like S3, which triggers a Lambda function to process the image. The processed file is then saved back to storage, and the main application is notified via a message queue like Amazon SQS. This keeps the core application simple while improving scalability and cost efficiency for specific operations.

However, integrating serverless requires addressing challenges like state management and latency. Serverless functions are stateless, so persistent data must be stored in databases or external services. For instance, a legacy application using serverless authentication might rely on AWS Cognito for user management, with tokens passed back to the main system via API calls. Monitoring also becomes more complex, as logs and metrics for serverless components are often scattered across cloud services. Tools like AWS X-Ray or Datadog can help unify observability. By starting with small, non-critical tasks and ensuring clear communication between components, teams can incrementally adopt serverless without disrupting existing workflows.