ZDM Implementing a L4 switch with Middle Tier servers

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Implementing a L4 switch with Middle Tier servers

Configure Sticky Sessions

  • Setup for the HTTP (80) port.
  • Setup for the SSL (443) port if Zen agents access the Middle Tier server over the SSL port.
  • Configure Sticky session timeouts to the same session timeout as the web server (IIS or Apache).

Configuring the L4 switch to detect if the Middle Tier server is down

  • Send and HTTP request to each Middle Tier Server
    • Server should return “HEAD /"
The “HEAD /" is the start of a HTML page so if the web server is down, then 
“HEAD /" will not be returned. When this happens, the L4 should configured to 
mark the server as down and redirect all traffic to another Middle Tier server.

Supported HTTP Protocol Error Codes by the Middle Tier

  • 204 – No Content
  • 400 – Bad Request
  • 404 – Not Found
  • 500 – Server Error
  • 503 – Out of Resources

There are other errors codes that can be implemented to help the L4 switch in detecting a server failure. Certain error codes can cause more traffic or the L4 can also put the Middle Tier server into a bad state and forcing all traffic to a single server if implemented incorrectly. The error codes should be implemented with care.