How does the bridge between the raw S3 bucket and the first Lambda function work, and how is the second Lambda function triggered by an event?

When a file is uploaded to the raw S3 bucket, you can configure an S3 event notification that publishes a message to an EventBridge event bus or directly invokes a Lambda function. The first Lambda function receives the event, processes the data, and can either publish a new event to EventBridge or invoke the second Lambda directly. If you use EventBridge, you create a rule that matches the event pattern (e.g., source = "aws.s3", detail-type = "Object Created") and routes it to the second Lambda. This decouples the two functions and allows the second to run only when the first signals completion. Alternatively, the first Lambda can call the second via the AWS SDK (lambda.invoke) after its work is done. In both cases, the bridge is the event notification mechanism (S3 → EventBridge or S3 → Lambda) and the subsequent event or invocation that triggers the second function.