Kafka is the platform for stream processing. The real power of Kafka comes in the scenario of distributed computing where Kafka logs can be considered as a single source of ordered-truths. Those logs can be consumed by all the relevant consumers in their own pace and own time. (within the retention period, of course). Here is a great LinkedIn blog on log, which is the core of Kafka platform. In summary, Kafka has a number of clustered broker nodes (which actually store message inside various topics which can be partitioned (default is 3)).

Microservice architecture is a philosophy of decoupling an otherwise large monolithic application into different independent modules (applications) interconnected with one another as well as external data sources using APIs. Message queuing comes into play in order to handle these inter-microservice and microservices-external-source communications, be it API calls or intensive data processing, blocking threads for which using synchronous model would render the entire application unresponsive. Apache Kafka is one such platform. Officially, it’s known as a distributed stream processing platform with high resilience and fault tolerance.