ZDM Implementing a L4 switch with Middle Tier servers

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Implementing a L4 switch with Middle Tier servers

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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).
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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.
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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.

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