GUI ScreenIO Client/Server

www.ScreenIO.com


Server Farms

In general you will be pleasantly surprised at the processing capability of even modest hardware when used as a server.  The very nature of transaction oriented processing as found in most COBOL applications does not impose a great load on a computer.   

If you have a large number of users accessing your applications you may eventually find that you are reaching the capacity of your server.  This is especially true for applications that are large in size and use a lot of memory, or where the available hardware does not have sufficient processing capacity.

In this case, you may configure a group of servers to act as a server farm. 

Licensing

Each server in a server farm requires a unique license. 

It is a copyright violation to use the same license in multiple servers, or to use an unlicensed server in a server farm.  If you do, the unlicensed server will detect the copyright violation and refuse to accept clients. 

Clients will receive a "Copyright violation on server" message when they attempt to connect.

Configuration

The principal machine in a server farm will hand off connections to other servers in the farm when it reaches its reserve threshold.   

You can use the reserve threshold to balance the load among the servers in your server farm.  The reserve threshold can be set below the maximum number of (licensed) connections, which causes the server to pass incoming connections to other servers before it reaches its maximum number of clients. 

When all of the servers in a server farm have reached their reserve thresholds, they will begin to accept connections again, until they have reached their maximum. 

To use a farm, you configure each server identically, or configure the first, and then copy the configuration files to the other farm members.  If located on the same network, all servers in the farm can use the same set of configuration files.

Your software must be installed in each server or it must be able to access this software on your local network. 

 

The items appear in this table in appearance order.

Item Significance
Server Farm This checkbox turns on the farm capabilities. You must turn on the farm in order to edit any of the other fields, and you may then turn it off and still retain the settings for later use.
Public Server IP

IP address of each server in the farm.  Note that this must be the PUBLIC IP to which clients will be re-directed, which may not be the same as the machine's real IP.

 

Example: Assume you have two servers behind a firewall on an internal network. This network has IPs in the 10.x.x.x subnet.  You are connected to the internet with a cable modem, IDSN, or DSL line.

  • Your clients will not be able to "see" your local IPs (10.x.x.x) because these are protected by your firewall.

  • When the first server needs to re-direct a client to another server farm member, it must tell the client the IP and Port to use to find the other server.  

  • In the case of a firewall, all connections will use the single external (Public) IP of the firewall, but each farm member will use a different port.

  • So the IP and PORT that you enter here are the IP and Port as seen from the Client.  Servers will pass these IPs and Ports to the client when they refer the client to a different farm member.

  • It is your firewall's job to route connection attempts on specific ports to the proper machine.  This is beyond the scope of this manual, but generally means directing all TCP traffic on a given port to a given IP on your local network.

If your servers are directly connected to the Internet (seldom a good idea with a Windows operating system), then each machine may have a different IP and the same port.

 

In any case, either the port or the IP must be different for each farm server.  Your first farm server should have the port and IP that you tell your users.  They need never worry about changing settings to use the farm, it will be automatic.  You need not and should not reveal the farm members IP/Ports.

 

NOTE:  These IP numbers are entered with all leading zeros shown for each octet (three digit group).  This makes it easier to scan them for uniqueness.  They will be passed to the client with leading zeros suppressed as is the standard notation.

Public Port

See the discussion above. 

Listen on Public Port

It is some times easier to configure your firewall to simply route traffic on a port directly to the target farm server without having to also change the destination port.  

 

So traffic destined for the second farm server in the example shown above would arrive on port 2875, and the firewall would forward that traffic directly to port 2875 on the second machine (using its real IP, not the one shown above).

 

If you did not check this option, the server would listen on the port specified on the first page of this property sheet, and in that case your firewall would have to re-direct the traffic to this machine AND change the port number.  That's not particularly difficult, but its one more thing to explain to your cranky network guru.

Serial Number Enter each server's serial number.  (Help/About in the server daemon will reveal its serial number).
Reserve Reserve sets the threshold at which the server starts routing connections to the other servers.  

Example:

If you say reserve 60% and you have a 10 user license, it will route the 5th (and subsequent) connection attempt to the next server.

If that server is also "into its reserve", it in turn will route to the third server.  If ALL the servers are into their reserve, the connection will be routed "round robin" to the first, but a special flag will be set telling the first server to allocate a connection out of its reserved capacity if any is available.  If the first server is FULL, it will route to the second, etc.  

If the last server receives a round-robin referral and it is full it tells the remote client to try later.

Disable If a machine must be taken out of the farm for maintenance you can simply check the disable checkbox and other servers will not attempt to route to it.  REMEMBER to make this change in ALL the Servers if not using shared configuration file.

© 2000-2019 Norcom, all rights reserved 

TOC

Send feedback to Norcom