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Date:         Sun, 16 Dec 2007 20:16:21 +0100
Reply-To:     Reinhart Willers <willers@uni-duesseldorf.de>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Reinhart Willers <willers@uni-duesseldorf.de>
Organization: =?us-ascii?Q?Uni_Dusseldorf_Universitatsrechenzentrum?=
Subject:      Redundant license servers: more risk of failure instead of more
              safety?
Comments: cc: Christian Hiotu <chiotu@spss.com>,
          Albert Lang <albert.lang@uni-duesseldorf.de>,
          Axel Buchner <Axel.Buchner@uni-duesseldorf.de>,
          Siegmund_Switala@yahoo.com, Susanne Mayr
          <susanne.mayr@uni-duesseldorf.de>
Content-type: text/plain; charset=us-ascii

Hi, Testing the robustness of three redundant SPSS license servers we damaged the system so hard, that we needed one day work to get it work again. And even now the situation is not satisfactory. We were glad, that this happened in the testing phase. During normal work it would be a great disaster.

What we did: We established successfully three redundant servers. To test the reliability we finished the service completely on that server working as leader. The licenses were passed correctly to the second server in the hierarchy. In the second step this computer was rebooted and the leader started again. Thereafter the information about licenses was completely lost. Nobody got a license. In the administration tool the servers were shown in the in the initial state without any licenses. After several useless trials we shut down all servers and redistributed the original redundant license file 'lservrllf'. After that the servers worked again und distributed licenses, but the licenses where allocated to the second server in the hierarchy and stayed there. Stopping this server the licenses where not passed to any of the other tow servers. No licenses were distributed, when this server was stopped. Stopping one of the two others had no impact. So we lost redundancy.

Our design: Within our LAN two subnets A and B are to be served with SPSS 16. The leading server is located in subnet A', which is physically identical with A. The other two are in Subnet B. The leader run under Windows Server 2003, the other two use WinXP. No Windows firewalls are used. On all computers except the second one only the SPSS license server was installed additionally to the system software. On the second computer an other license server is also running using software from Aladdin. The university firewall was opened for UDP 5093 und TCP 5099. The SPSS-documentation requests UDP 5099, but this port is shown as closed and no traffic was reported on this port. Instead the servers talked on port TCP 5099 and UDP 5093 LSHOST and etc/hosts are defined on all servers. All servers use the Sentinel-server 8.1.

After this experience we have lost the confidence in the safety of redundant SPSS license servers. Such damage, we observed should be impossible. Apparently the communication of the servers is not protected against all unattended interrupts. But this is not the only thing, which got us thinking. There is no tool in the SPSS license server to control the conversation of the servers. Therefore it is very difficult to locate an error. But such an error is critical, since all the users are affected. And thirdly a reset after a serious damage seems to be to complicate, to be incorporated in an emergency plan. Therefore we think that in the present implementation redundant servers give not the protection, we need.

What is your opinion? Have you quit different experiences?

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