Enterprise Application Integration (EAI) is a concept that was spawned from the need to share data between multiple systems in the most efficient way. The premise behind EAI means creating an application (or suite of applications) to facilitate interactions between the many other applications that a business already has. Using the example of a retail store, they may have a Customer Relationship Management (CRM) system, supply chain system, and a payment system. All of these systems need to make decisions based on shared information. The contact information of a customer may be created or sourced in the CRM, and the invoicing system may also need this information to be able to create an invoice with the correct billing address:

Historically, the best way to achieve information sharing was through EAI. This would involve creating an integration application that all the other applications can connect to in order to exchange data. Like System E in the preceding diagram, adding a new application to an existing set of applications is simple because the new system only needs to connect to a single integration application. As a concept, this is brilliant because it easily allows applications to exchange data, but before serverless technologies there were constraints on how EAI could be implemented.

In the early days, these integration applications would have been hosted on a single monolithic server. The applications being integrated only had to be concerned about connecting to a single specific server. The downside to this was that there was now a single point of failure when attempting to communicate between any system, assuming the integration application was being used to facilitate all interactions occurring with the applications. If the integration application had a problem or went offline, every system would be adversely affected.

One key element that EAI achieved was enabling system-to-system communication in an event-driven flow. The importance of this will be explained as we delve deeper into serverless and the effect it has had on integration methods and patterns.

In the next section, we will move on to a more specific version of EAI by introducing the Enterprise Service Bus (ESB).