What is the difference between the role and interaction of one or more consumers in a message processing system?

In a message processing system, the role of the consumer is to receive and process messages from a queue or topic.

If there is only one consumer in the system, it processes all messages sequentially, ensuring simple order and control.

With multiple consumers:

• Messages are distributed among them (for example, through load balancing).
• This increases performance and scalability, as processing occurs in parallel.
• It is important to consider that message order may be disrupted if multiple consumers process different parts of the stream.

Interaction between consumers is usually minimal — they work independently but can coordinate through locking mechanisms or distributed transactions if consistency is required.

An example in Go using a channel for multiple consumers:

messages := make(chan string)

// Launch multiple consumers
for i := 0; i < 3; i++ {
    go func(id int) {
        for msg := range messages {
            fmt.Printf("Consumer %d processed message: %s\n", id, msg)
        }
    }(i)
}

// Sending messages
messages <- "msg1"
messages <- "msg2"
close(messages)

Here, three consumers process messages from a single channel in parallel.