Kafka best practices edition → How to design Kafka message key and why it is important in determining application performance?

What is a Kafka Message: A record or unit of data within Kafka. Each message has a key and a value, and optionally headers.The key is commonly used for data about the message and the value is the body of the message

Message Key → Can be null or contain some value that say’s something about data, like user/email id or hash of message e.t.c