Serverless services run your code and route your events without you managing servers. They scale automatically, including down to zero, and you pay for use rather than for idle capacity. Event-driven design means components react to events, such as an object uploaded or an order placed, instead of calling each other directly, which keeps them loosely coupled. On the exam, serverless is often the answer when a question stresses the least operational overhead, unpredictable or spiky traffic, or paying nothing when idle. AWS Lambda runs functions in response to events: an API request, a new object in S3, a message in SQS, a record in a DynamoDB stream or Kinesis stream, or a schedule. You choose the memory size, which also sets the CPU share, and a timeout of up to 15 minutes. Each function has an execution role that grants its AWS permissions. Lambda scales by running more concurrent copies; reserved concurrency guarantees and caps capacity for one function, which also protects a downstream database from being overwhelmed, and provisioned concurrency keeps instances initialized to avoid cold-start latency. Asynchronous invocations can send failures to a destination or DLQ. Lambda can run in a VPC to reach private resources such as RDS, often through RDS Proxy to pool connections. Anything that runs longer than 15 minutes or needs a persistent process belongs on containers, AWS Batch or EC2 instead.
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