The Azure Relay service facilitates hybrid applications by enabling you to securely expose services that reside within a corporate enterprise network to the public cloud, without having to open a firewall connection, or require intrusive changes to a corporate network infrastructure. Relay supports a variety of different transport protocols and web services standards.

The relay service supports traditional one-way, request/response, and peer-to-peer traffic. It also supports event distribution at internet-scope to enable publish/subscribe scenarios and bi-directional socket communication for increased point-to-point efficiency.

In the relayed data transfer pattern, an on-premises service connects to the relay service through an outbound port and creates a bi-directional socket for communication tied to a particular rendezvous address. The client can then communicate with the on-premises service by sending traffic to the relay service targeting the rendezvous address. The relay service then "relays" data to the on-premises service through a bi-directional socket dedicated to each client. The client does not need a direct connection to the on-premises service, it is not required to know where the service resides, and the on-premises service does not need any inbound ports open on the firewall.

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