How can a service and its consumers accommodate isolated failures and avoid unnecessarily locking resources?:
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Problem |
When a service capability requires that consumers interact with it synchronously, it can inhibit performance and compromise reliability. |
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Solution |
A service can exchange messages with its consumers through an intermediary buffer, allowing services and consumers to process messages independently by remaining temporally decoupled. |
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Impacts |
There may be no acknowledgment of successful message delivery, and atomic transactions may not be possible. |
Problem: Synchronous communication requires an immediate response to each request, and therefore forces two-way data exchange for every service interaction. When services need to carry out synchronous communication, both service and service consumer must be available and ready to complete the data exchange. This can introduce reliability issues when either the service cannot guarantee its availability to receive the request message or the service consumer cannot guarantee its availability to receive the response to its request. Because of its sequential nature, synchronous message exchanges can further impose processing overhead, as the service consumer needs to wait until it receives a response from its original request before proceeding to its next action. Prolonged responses can introduce latency by temporarily locking both consumer and service.
Another problem forced synchronous communication can cause is an overload of services required to facilitate a great deal of concurrent access. Because services are expected to process requests as soon as they are received, usage thresholds can be more easily reached, thereby exposing the service to multi-consumer latency or overall failure.
Solution: A queue is introduced as an intermediary buffer that receives request messages and then forwards them on behalf of the service consumers. If the target service is unavailable, the queue acts as temporary storage and retains the message. It then periodically attempts retransmission. Similarly, if there is a response, it can be issued through the same queue that will forward it back to the service consumer when the consumer is available. While either service or consumer is processing message contents, the other can deactivate itself (or move on to other processing) in order to minimize memory consumption.