Email Gateway Queue Replication for Stateful Failover
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Solution Overview
Problem
Email gateways in SMTP systems are a weak link in message delivery, prone to delays and losses due to unreliability, especially with large message volumes and the growing commercial and legal value of email content, where messages can be stuck or lost if the target server is unavailable or fails, leading to significant costs for organizations.
Innovation Solution
A method for replicating SMTP queues between clustered email gateway systems, where messages are stored on a source gateway and redundantly replicated to sink gateways, with monitoring for system failures and automatic alarm and delivery mechanisms to prevent message loss, ensuring timely and reliable delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If messages are queued on a single email gateway for relay, then message delivery can be managed centrally, but message loss and delays occur when the gateway fails or the target server is unavailable
Solution Approach 1:
The patent implements queue replication by creating copies of message queues from source email gateways to sink email gateways. When the source gateway fails or messages are stuck, the replicated queues on sink gateways can take over and continue delivery, preventing message loss and reducing delivery delays.
Solution Approach 2:
The patent performs preliminary replication of message queues to sink gateways before the source gateway fails. This advance preparation ensures that backup copies are already available, enabling immediate failover without waiting for failure detection, thus improving reliability and reducing delivery delays.
2Reliability
If message queues are replicated to multiple sink gateways, then redundancy and failover capability improve, but system complexity increases
Solution Approach 1:
The patent implements monitoring mechanisms that track the status of source and sink gateways. When failures are detected, the system automatically triggers failover procedures. This feedback loop manages the complexity of multi-gateway replication by providing automated control, reducing the need for manual intervention despite the increased system complexity.
3Reliability
If the source email gateway continuously retries delivery to unavailable target servers, then eventual delivery may be achieved, but message queues grow large and delivery delays increase
Solution Approach 1:
The patent introduces sink gateways as intermediaries in the message delivery system. Instead of the source gateway directly retrying deliveries to unavailable target servers, the replicated queues on sink gateways can act as intermediate storage and retry points, distributing the retry burden and reducing queue growth at the source gateway.
Data Source
AI summary
A method of “stateful failover” is provided that allows email gateway systems in a cluster to deliver email messages that have been accepted for delivery by a member of the cluster, but has failed with out delivering the messages. The method involves creating a backup copy of the messages that have been accepted for delivery by one email gateway system in the stateful failover cluster on one or more other email gateway systems in the stateful failover cluster. Upon detecting the failure of the email gateway system that accepted the message, another member of the stateful failover cluster that has access to the backup copy of the message queue takes responsibility for the delivery of the messages on the mirrored queue.