✉️ Events and commands

A command asks a specific recipient to do something, and the recipient may refuse. An event states a fact that already happened and goes to anyone who listens. The definitions are short; telling the two apart in a real system is harder. After reading, you’ll be able to decide which one a given message should be.

There’s one article here. It explains why “commands are synchronous, events are asynchronous” is a habit, not a rule, and gives a practical test: if the recipient has the right to refuse, send a command; if it should just accept, publish an event. It also covers a common trap: an event with exactly one recipient that must always handle it. Often that’s a command sent under an event’s name.

Read it before you design the messages between your modules. The Events on the inside, events on the outside guide continues from there.