Sensors and External Triggers

Concepts covered: paSensors, paExternalTriggers

A pipeline often has to wait for something outside its control. A vendor SFTP drops a file at an irregular time. A REST API publishes a daily endpoint that becomes available between 1am and 4am. A Kafka topic accumulates messages, and a downstream batch process should kick off when the offset crosses a threshold. Sensors are the orchestration primitive that turns 'wait for the world' into a task the DAG can schedule around. Knowing the families of sensors and their trade-offs is part of the intermediate vocabulary. What a Sensor Is, Precisely A sensor is a task that periodically checks an external condition and succeeds when the condition becomes true. The condition can be 'a file exists in this S3 prefix', 'this API endpoint returns 200', 'this Kafka offset is at least N', 'this upstream

About This Interactive Section

This section is part of the Orchestration and Dependencies: Intermediate lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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