Service Bus Relay is an Azure service which facilitates hybrid applications by enabling secure connectivity between services hosted on Azure and Windows Communication Foundation (WCF) services hosted on premise. The Service Bus can listen for incoming external connections and provide granular security controls for access to services.
Hybrid Connections is a feature of Azure App Service BizTalk API Apps to make connections from Azure Web Apps and Mobile Services to on premise resources using static TCP ports (e.g. SQL, MySQL & web services). This service can be used to facilitate staged migrations to Azure by maintaining hybrid connectivity. Hybrid Connection Manager must be installed on premise by navigating to the BizTalk API Apps service in the Azure portal .
Azure Web Apps may be integrated with Azure Virtual Networks to provide access to the resources on the network and also connected resources on premise. VPN connections to other networks are limited to 6 on premise networks and 4 additional virtual networks for a maximum of 10 connections (Basic & Standard). High Performance VPN Gateways allow up to 30 connections.
Both Virtual Machines and Cloud Services can be joined to a domain. For Virtual Machines this can be done manually on the server or through PowerShell scripts. For Cloud Services PowerShell scripts can be configured as a Startup Task or it is also possible to add code to the RoleEntryPoint of the Cloud Service however this requires the Cloud Service to be run in elevated mode rather which is a less secure option.