Messages

Introduction#

• A wrapper around the data which the sender wants to send.
• it is a format which is understandable by every component of the messaging system
• it is the moving component in the messaging system

Message structure#

Header #

• It is the metadata of the message. 
• The sender can use the header to send any information that is related to the message but not part of the payload.
• Such information can be :
  • Message ID: A unique ID of each message. works as an idempotent ID.
  • Correlation ID (Trace ID): useful to trace a request across services.
  • Message Group ID: useful in the grouping of the messages. 
  • Sequence Number: useful in the ordering of the messages.
  • Expiry Time: tells when the message will expire.
  • Creation Time: tells when the message was created.

Payload#

• The actual piece of data which is intended to be transferred.
• Based on the intent of the data, the payload can be categorized into 3 types
  • Action: The intent is to ask the receiver to perform some action like CREATE_SHIPMENT or GET_ORDER.
  • Event: The intent is to notify about an event that happened like ORDER_CREATED.
  • Document: The intent is to pass the data of either event or entity.