dfe-transform-vector documentation

How dfe-transform-vector is built and configured, and how to move a pipeline onto it from Vector.

• Architecture
• DFE Transform Vector -- Design Document
• librdkafka Configuration Reference
• Migration Guide: Vector -> dfe-transform-vector
• config-schema.yaml -- the configuration as a JSON Schema (YAML)
• config-schema.json -- the configuration as a JSON Schema (JSON)
• capability-catalog.yaml -- what the app can do, as a catalogue (YAML)
• capability-catalog.json -- what the app can do, as a catalogue (JSON)