What it is: Event sources that invoke (call) a Lambda function.

What it’s for:

• Automatically run code when something happens in AWS.

Common triggers (exam staples):

• S3 events (ObjectCreated)
• DynamoDB Streams
• API Gateway requests
• EventBridge schedules/rules
• SQS messages / SNS notifications

Key ideas:

• A trigger defines when Lambda runs.
• Some triggers push events to Lambda; others Lambda polls (e.g., SQS) (conceptually).

Exam cues:

• “process each message from queue” → SQS trigger.
• “run every hour” → schedule trigger (EventBridge).

Hard words:

• *invoke* /ɪnˈvoʊk/: gọi chạy (hàm)
• *event source* /ɪˈvent sɔːrs/: nguồn sự kiện
• *poll* /poʊl/: thăm dò (hỏi định kỳ)