When we start deploying multiple application, they will inevitably need to communicate with one-another. There are 2 types of communication pattern:

• Synchronous Communication (Application to Application)
• Asynchronous / Event Based (App -> Queue -> App)

# Few Technologies that help us with Event Based Architecture

    1. Amazon SQS       : Queue Model
    2. Apache Kafka     : Publisher/Subscriber Model
    3. RabbitMQ         : Realtime Data Streaming Model
    ...

Synchronous Applications/Communication can be problematic if there is a sudden spike in traffic. What if you suddenly need to encode 1000s of videos instead of 10? (assume 10 is usual load)

In that case it is better to decouple(for eg. Buyer & Seller) your application. Their services (Buyer/Shipping), once decoupled can scale independently.