Introduction to AWS Lambda

AWS Lambda is Amazon's serverless compute service. You upload your code, configure a trigger, and Lambda runs your function in response to events — scaling automatically from zero to thousands of concurrent executions. There are no servers to provision, no operating systems to patch, and no capacity to plan.

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How Lambda Works — The Execution Model

When an event triggers a Lambda function, the following sequence occurs:

Event Source           Lambda Service            Execution Environment
+-----------+        +----------------+        +---------------------+
|  API GW   | -----> |  Invoke API    | -----> | Init runtime        |
|  S3 Event |        |  Route event   |        | Load function code  |
|  SQS Msg  |        |  Scale if      |        | Execute handler()   |
|  Schedule |        |  needed        |        | Return response     |
+-----------+        +----------------+        +---------------------+

1. Event arrives — an HTTP request, S3 upload, SQS message, or scheduled timer
2. Lambda service receives the invocation request
3. Execution environment is created (cold start) or reused (warm start)
4. Handler function runs with the event payload
5. Response is returned to the caller (synchronous) or acknowledged (asynchronous)

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Supported Runtimes