When is it appropriate to use message queues for communication between microservices?

Message queues between microservices are used when it is necessary to ensure:

• Asynchronous communication: services do not depend on immediate responses from each other.
• Reliability: messages are stored in the queue until the recipient processes them.
• Scalability: it is easy to add message consumers to handle load.
• Decoupling of components: services do not know about each other's internals, interacting through messages.

Using queues is advisable if microservices need to exchange data with guaranteed delivery, process events in the order received, or when load balancing and fault tolerance are required.

For example, in an order system, the ordering service can send messages to the queue, and the payment processing service can handle them asynchronously.