Apache Kafka is best used when building real-time data pipelines and streaming applications due to its high throughput, durability, and ability to handle large volumes of data with low latency. It excels in use cases where consistent message delivery and stream processing are critical, such as in financial services for transaction processing or real-time analytics. For instance, if you need to collect and process millions of event logs from various services in real-time, Kafka would be the preferred choice over NiFi.
Apache NiFi is ideal for scenarios where you need to design complex data flows visually, manage data routing, and perform real-time data transformations without extensive coding. It's particularly useful when dealing with diverse data sources and the need for custom logic in data handling. For example, if you need to pull data from various APIs, transform it, and then send it to different databases or services with a user-friendly approach, NiFi would be preferable due to its visual interface and capabilities.