Event interception

Oct 2020

As many more companies migrate away from their legacy systems, we feel it's worth highlighting an alternative to change data capture (CDC) as a mechanism for getting data from these systems. Martin Fowler described event interception back in 2004. In modern terms it involves forking requests on ingress to a system so that it's possible to gradually build a replacement. Often this is done by copying events or messages but forking HTTP requests is equally valid. Examples include forking events from point-of-sale systems before they're written to a mainframe and forking payment transactions before they're written to a core banking system. Both lead to the gradual replacement of parts of the legacy systems. We feel that as a technique, obtaining state changes from the source, rather than trying to recreate them postprocessing using CDC, has been overlooked which is why we're highlighting it in this issue of the Radar.