Azure Service Bus Topics - How communication works over HTTP (80,443)

In this topic we will talk about different protocols and ports that can be used to communicate between our machines and Azure Service Bus Topics.
The communication between Azure Service Bus Topic and our machines we can use:

• AMQP (new and hot)
• TCP/IP
• HTTP

For TCP/IP connection is pretty clear what ports are used (9351 and 9552). It seems that 9351 is used for inbound traffic and 9552 is used for outbound traffic (this ports may change)

The interesting discussion is when we are taking about HTTP. The communication over HTTP protocol is done over two ports - 443 and 80.

Each port is used for specific use case:

• 80:   is used for outbound traffic
• 443: is used for inbound traffic

This means that when we are listening to a subscription we will use port 80 to check if a message is available. The same port will be used to receive the message from subscription. 

The port 443 is used when we need to send messages to topic. Each time when we send a message to a topic, the message is send over 443 without exception. 

For both ports (80 and 443), the communication is done done using a TLS/SSL. Even if port 80 is used, the communication is secure - inside a tunnel. No data in clear are send between our application and Azure Service Bus.
It is important to know that Azure Service Bus doesn't supports unsecure connection. All the communication will be done over a secure tunnel.

If the connectivity mode is not change (AutoDetect), the Azure Service Bus library will try to use TCP/IP connection. If the connection cannot be established using the 9XXX ports, it will fall back automatically to HTTP ports.

We have the possibility to specify directly what kind of connectivity mode we want to use (AutoDetect/TCP/HTTP). This is useful when we already know the connectivity type. 

The below sample shows how we can configure it.

HTTP: ServiceBusEnvironment.SystemConnectivity.Mode = ConnectivityMode.Http;

TCP:  ServiceBusEnvironment.SystemConnectivity.Mode = ConnectivityMode.Tcp;

Auto: ServiceBusEnvironment.SystemConnectivity.Mode = ConnectivityMode.AutoDetect;

In conclusion we should keep in mind that all the communication between Azure Service Bus endpoint and our system is done over a secure channel. For HTTP connection, a tunnel is establish over 80 and 443 ports.