pubsub

different level of message guarantees:

• at-least-once delivery (may be duplicated)
• at-most-once delivery (may not be delivered at all)
• exactly-once delivery (eliminates duplicates and ensures delivery)

messages in a pub-sub system can be of various formats, such as

• JSON
• XML
• binary
• avro
• protobuf

message broker architecture:

• they can be clustered for high avaliability and scalability
• messages are stored in
  • memory
  • on disk
  • distributed storage system
• messages can be replicated across nodes to ensure durability
• topics can be partitioned to distribute the load across multiple nodes
• offset management tracks which messages have been consumed to ensure correct delivery

we can persist messages in a durable store that allows subscribers to receive messages even if they are offline when the messages are published, once they come online, they can recieve the persisted messages

apache kafka, rabbitmq, aws sns are some of the other message brokers