Within AWS Glue, crawlers and ETL jobs do different things, and the Data Engineer exam expects you to keep them straight.
Discover vs transform
A crawler scans your data, infers its schema, and populates the Glue Data Catalog — it discovers and catalogs, it doesn’t transform. An ETL job runs Spark/Python code to transform and move data. Need schema in the catalog? Crawler. Need to clean or reshape the data? ETL job.
Test yourself
A team needs to automatically detect the schema of new files landing in S3 and register it so Athena can query them. Which Glue feature?
- A Glue ETL job
- A Glue crawler
- A Glue trigger only
- Glue DataBrew
👉 Click to reveal the answer & explanation
Correct answer: B. A Glue crawler scans the data, infers schema, and populates the Data Catalog for Athena to query. An ETL job (A) transforms data but isn’t primarily for schema discovery; a trigger (C) just schedules; DataBrew (D) is visual data prep.
Related topics
AWS Glue · Glue Data Catalog · Amazon Athena
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