Queue vs Topic (Pub/Sub)

Emit OrderPlaced. In a queue one worker grabs it; in a topic it fans out to everyone. Add a WhatsApp subscriber live.

Emitted: 0

🏭

Order Service

Producer

📡 Topic

OrderPlaced

✉️Email Service0

📱SMS Service0

🧩CRM Service0

📈Analytics0

🗂️Audit Log0

One event → every subscriber gets a copy. Watch all lanes light up together.

What just happened

▹Queue (competing consumers): each event is handled by exactly ONE worker — perfect for distributing background jobs.
▹Topic (pub/sub): every subscriber gets its OWN copy of the event — perfect for fan-out to Email, CRM, Analytics, Audit…
▹Add a WhatsApp subscriber live: it just starts receiving OrderPlaced. The producer never changed — that's loose coupling.