What is Amazon Lambda?
AWS Lambda is a serverless compute service that lets you run code without provisioning or managing servers. You upload your function code, define a trigger, and AWS executes the function in response to events.
At a conceptual level, Lambda is event-driven compute. Instead of running servers continuously, your code runs only when something happens:
- An HTTP request arrives (via API Gateway)
- A file is uploaded to S3
- A message appears in a queue
- A scheduled event triggers execution
How It Works Internally
When an event triggers a function:
- AWS provisions an isolated execution environment.
- Your function code is loaded.
- The handler runs.
- The environment may be reused for subsequent requests.
The first invocation may incur a cold start, where AWS initializes the runtime. Subsequent invocations may reuse the environment (warm start).
Why It Matters in System Design
Lambda changes how you think about compute:
- No long-running servers.
- No infrastructure patching.
- Automatic scaling by default.
- Pay only for execution time.
Architecturally, this shifts responsibility from capacity planning to event design and system orchestration.
Lambda Fundamentals
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What triggers a Lambda function?
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