In this example we would be developing a website or API component which was hosted in Azure Websites. In the application we are developing we need to reach down to an on premise resource and have chosen to use Azure BizTalk Hybrid Connections to allow us to do this. The below diagram shows how we can use the hybrid connections endpoint which will route data to the on premise hybrid connection agent which will then route the data stream to the on premise resource.
In this example the role played by the Azure Website is to act as a host for the web site component. This is a platform as a service hosting option which means it is not going to be part of a virtual network which you can connect to your on premise data centre using networking technologies. In this case we have chosen instead to use Azure BizTalk Services Hybrid Connections.
In the example we would create a hybrid connection endpoint in Azure and then install the on premise hybrid connection agent. When the developer of the website wants to access data from the on premise resource they would be using the same technique as they would pretty much use if they were on premise and on the same network as the resource. In the case of a SQL Database the developer could be using a standard SQL connection string and then when the website was deployed to Azure Websites they would modify the connection string to point to the Hybrid Connection endpoint instead.
When a request was executed the data would be sent to the hybrid connection endpoint and the stream would be routed to the on premise agent which would then forward it to the on premise database so the data could be retrieved.
The role of the hybrid connection is to provide a simple way to be able to access those on premise resources.