Sample scripts to generate alerts and record server failure

Load Balancer provides user exits that trigger scripts that you can customize. You can create the scripts to perform automated actions, such as alerting an Administrator when servers are marked down by the manager or simply record the event of the failure.

Sample scripts, which you can customize, are in the install_root/servers/samples directory. In order to run the files, you must move them to the install_root/servers/bin directory and remove the ″sample″ file extension. The following sample scripts are provided:
  • serverDown — a server is marked down by the manager.
  • serverUp — a server is marked back up by the manager.
  • managerAlert — all servers are marked down for a particular port.
  • managerClear — at least one server is now up, after all were marked down for a particular port.

If all servers on a cluster are marked down (either by the user or by the advisors), the managerAlert (if configured) starts, and Load Balancer attempts to route traffic to the servers using a round-robin technique. The serverDown script does not start when the last server in the cluster is detected as offline. By design, Load Balancer attempts to continue to route the traffic in case a server comes back online and responds to the request. If Load Balancer instead dropped all traffic, the client would receive no response. When Load Balancer detects that the first server of a cluster is back online, the managerClear script (if configured) starts, but the serverUp script (if configured) is not run until an additional server is brought back online.

Here are some considerations for using the serverUp and serverDown scripts:
  • If you define the manager cycle to be less than 25% of the advisor time, false reports of servers up or down can result. By default, the manager runs every 2 seconds, but the advisor runs every 7 seconds. Therefore, the manager expects new advisor information within 4 cycles. However, removing this restriction (that is, defining the manager cycle to be greater than 25% of the advisor time) significantly decreases performance because multiple advisors can advise on a single server.
  • When a server goes down, the serverDown script starts. However, if you issue a serverUp command, it is assumed that the server is up until the manager obtains new information from the advisor cycle. If the server is still down, the serverDown script runs again.