meddelandeköer

Meddelelandekoer (Swedish for "message queues") are a class of messaging systems that enable asynchronous communication by storing and forwarding messages between producers and consumers. They decouple components, improve resilience, and help balance load in distributed applications.

In a typical setup, producers send messages to a queue or topic. The queue persists messages until a consumer retrieves and processes them. Depending on the pattern, multiple consumers may share a queue (competing consumers) or subscribe to a topic (publish–subscribe). Messages can be processed once or may be retried on failure, and some systems support multiple delivery guarantees and ordering options.

Key properties include durability (persistence across restarts), delivery semantics (at-least-once, at-most-once, or exactly-once with varying guarantees), ordering (FIFO versus non-deterministic delivery), and fault-tolerance features such as acknowledgments, retries, and dead-letter queues. Semantics and guarantees vary by implementation and configuration.

Common types include point-to-point queues and publish-subscribe topics; many systems provide both. Implementations range from traditional brokered systems such as RabbitMQ and ActiveMQ to distributed log services such as Apache Kafka and cloud services like Amazon SQS or Azure Service Bus. Kafka, in particular, uses topics and partitions with retained logs, which differs from a classic queue model but serves similar purposes in stream processing.

Use cases include asynchronous task processing, event-driven architectures, service decoupling, load leveling, and reliable communication between microservices. Design considerations include throughput, latency, ordering requirements, scalability, and operational concerns such as monitoring and failure handling. See also: message broker, publish–subscribe, and queues.