Queue

A collection of entities that are maintained in a sequence and can be modified by the addition of entities at one end of the sequence and the removal of entities from the other end.

A queue is a data structure and messaging pattern that processes items in a first-in, first-out (FIFO) order. In distributed systems, message queues are used to decouple producers (services that create work) from consumers (services that process work), enabling asynchronous communication between components.

Message queue services include Amazon SQS, RabbitMQ, Apache Kafka (which also supports pub-sub patterns), and Cloudflare Queues. These services guarantee message delivery, handle retries for failed processing, and buffer traffic spikes to protect downstream services from being overwhelmed.

In API architectures, queues enable asynchronous request processing. An API gateway can accept a client request, place it on a queue, and return an immediate acknowledgment (such as an HTTP 202 Accepted response). A background worker then processes the queued request at its own pace. This pattern is useful for long-running operations like file processing, email sending, or data imports, where making the client wait for completion would cause timeouts or poor user experience.