Configuring a Three-Server Redundancy Cluster

Configure SySAM for redundancy by setting up a three-server redundant cluster.

Prerequisites

The three machines hosting a license server should:

Have excellent communications.
Maintain identical copies of the license files, the lmgrd binary, and the SYBASE binary locally rather than on a file server. If you do not do this, you lose the advantages of having redundant servers, since the file server holding these files becomes a single point of failure.

Task

A three-server redundancy is functional when any two of the three license server systems are running. Three-server redundancy only provides failover protection; it does not provide load balancing.

Copy the license file to the licenses directory of each of the three servers. Each line contains the name of the server, its host ID, and the port number on which it will listen. For example:
```
SERVER server_1 0123ABCD 27010
SERVER server_2 0456DCBA 27010
SERVER server_3 07890147 27010
```
The selection order for the master server is determined by the order in which you specify the servers at SPDC or SMP and can be seen by the order of the servers in the resultant license file. The same license file must be used by each license server and is headed with a SERVER line for each server.
SySAM-enabled products must be informed to obtain licenses from a three-server redundant cluster so that they can fail over to the new master server if the current master becomes unavailable. Set this up in one of these ways:
- Sybase recommends that the license file used by the product is headed with three SERVER lines. The header must be identical to that of the license files on each server, with the exception that the host ID field can be set to ANY. The following license file enables a product to use the three-server redundant cluster shown in the example above:
```
SERVER server_1 ANY 27010
SERVER server_2 ANY 27010
SERVER server_3 ANY 27010
USE_SERVER
```
- Alternatively, set the SYBASE_LICENSE_FILE or LM_LICENSE_FILE environment variables to a comma-separated list of port@hostname values to specify the three-server redundant cluster. For the example above, set the environment variable to:
```
27010@server_1,27010@server_2,27010@server_3
```
  Note: If the machine where the product is running must use a fully qualified domain name (FQDN) to contact any license server in the cluster, you must specify the FQDN in the environment variable and also when generating the license at SPDC or SMP.