Handling Connections (Magic xpa 3.x)

The connections between the various parts of the distributed application architecture remain as long as both sides of the connection are alive and functioning. The operating system "netstat" command helps view these connections during different phases of the TCP/IP state diagram.

A requester, such as ISAPI, initially starts a connection to the broker and to each enterprise server. These connections stay ESTABLISHED until the requester or the partner, that is the broker or an enterprise server, is shut down.

When a requester needs to send a request to the broker or an enterprise server and all established connections are already in use, the requester opens a new connection and keeps it ESTABLISHED, as described above. This means that the number of established connections grows gradually until it reaches a maximum number of connections, and then the existing connections serve all further requests without opening new connections. There is only one connection from each enterprise server to the broker.

If the requester shuts down, such as when an IIS restarts, the requester closes its connections to both the broker and all connected enterprise servers gracefully. Then the requester starts opening new connections, exactly as described previously.

If the broker or enterprise servers are shut down without the requester knowing about it, the CLOSE_WAIT status message appears on the requester's side, and the FIN_WAIT_2 message appears on the broker’s or enterprise server’s side.