Designing systems that take advantage of modern platforms, tools, and techniques is critical for building scalable, evolvable applications that underpin businesses of all stripes. Leveraging those when your data is captured in a mainframe, which does not scale well, is challenging. Technical and architectural debt is often a stifling element and the momentum to modernize can be both hard to gain and to maintain.

This talk discusses how National Grid built an event driven system using change data capture on top of a DB2 mainframe to power a cloud native GraphQL API hosted in Azure.

National Grid uses mainframes to power their customer billing capabilities. These mainframes encompass decades of data and capabilities in a monolithic, inelastic system. Many business and customer channels rely on this data and functionality. The motivating application for our project is the customer web portal. Earlier iterations of the portal relied on direct synchronous calls to the mainframe. This constraint historically caused problems for scaling to their customer base’s needs on the web. Availability and performance were key challenges.

Our architecture works by disconnecting the needs of the web application from the constraints of the mainframe. This ‘system of reference’ is hosted in the cloud with modern tech and is far better suited to adapting to business and (by extension) customer needs. It is a foundation which can, and is, being built upon to modernize National Grid’s technology portfolio, with no direct dependency on the legacy systems underlying them.

• Change data capture enables near-real time synchronization
• The ‘Customer Graph’ system-of-reference provides capability to scale independently from mainframe and be resilient to on-prem volatility
• Asynchronous boundaries between cloud/on-prem resources decouples applications from connectivity/availability issues
• APIs developed with domain-driven design, providing multi-channel support for diverse business applications