Configuring Server Farms

You use the Farm Table window to monitor, insert and edit server farm information.

To define a server farm:

  1. From the WSD menu, select Farms > Farm Table. The Farms window appears, which contains the following parameters:

    Parameter

    Description

    IP Address:

     A virtual IP address representing the farm to the clients.

    Farm Name:

    Enter a name, up to 50 characters in length, to describe the WSD farm.

    Admin Status:

    Can be one of the following options:

    • Enable: The farm is active. All users are balanced between  the servers.

    • Disable: The farm is inactive. Clients connecting to the farm will not be served.

    Aging Time [sec]:

    The amount of time a non-active client is kept in the client table (in seconds). As long as a client is kept in the client table, the client will be connected to the same server.

    Dispatch Method:

    The method used to determine to which server in the farm traffic will be directed:

    Cyclic: Directs traffic to each healthy server one by one  (round robin).

    Weighted Cyclic: WSD version 7.20 introduces this new Dispatch Method. This method uses the Weighted  Round Robin algorithm and respects a servers  weight.

    Least Traffic: Directs traffic to the server with the least traffic.

    Least Users Number: Directs traffic to the server with the least amount of users.

    Local Least Traffic: Directs users to the server with the  least traffic, from this farm only, for example, traffic from  other farms is not considered.

    Local Least Users Number: Directs users to the server with the fewest users, from this farm only, for example, users of other farms are not considered.

    nt-1: The WSD starts querying the farm's servers for  Windows NT SNMP statistics. The WSD redirects the farm's clients to the least busy server according to the servers' reported statistics. This method may be used only with Windows NT servers. The parameters are considered according to the weights configured in the first Windows NT weights scheme.

    nt-2: Similar to nt-1, but using the second weights scheme.

    private-1: When choosing this method, the WSD will query the farm's servers for private SNMP parameters, as defined in the first private weights scheme. The ratios of users on the servers will be balanced according to the reported statistics.

    private-2: Similar to private-1, but using the second  weights scheme.

    Response Time: Enables Response Time load balancing. This method load balances the servers in the farm based on the least loaded server as calculated by the Response Level.

    Hashing: When selected, WSD performs a static Hash function in order to select a server for this session. The input for the hash function can be determined by the Client Table mode, it can be either source and destination IP addresses, source and destination IP addresses and ports, source IP only, or destination IP only. This is a static method where the server is chosen for a session purely by the session information. If the farm is part of a URL SuperFarm, the input function for the Hash is the requested URL.

     

    Connectivity Check Method:

    Indicates the method of checking for server availability. You can choose Ping, TCP Port, UDP Port and HTTP Page. If Ping is selected, the WSD pings the servers to verify valid communication. If HTTP Page is selected, the WSD will try to retrieve the web page (as configured in the Home Page field) from the servers. TCP Port or UDP Port causes the WSD to attempt to connect to the specified application port, according to the protocol. If a Ping operation fails, or a session could not be opened, this means that the server is down.

    Connectivity Check Port:

    The specific port to which to conduct the connectivity check. The value can be FTP, HTTP, SMTP, DNS, NNTP, HTTPS, or any port number you enter manually. For example, "HTTP" automatically checks port 80.

    Connectivity Check Interval:

    How often the Web Server Director polls the servers (in seconds).

    Connectivity Retries:

    The number of polling attempts that should be made before a server is considered inactive. This also applies to the reports from other WSD DS/NP devices.

    Multiplexed Farm Port:

    Enables applications on the servers to be available on different ports. Multiplexed ports can be defined in each farm. The value can be FTP, HTTP, SMTP, DNS, NNTP, HTTPS, Disable, or any port number you enter manually.

    Distribution Threshold (WSD DS/NP only):

    Determines the threshold of the number of users served by the local (regular) servers; above this threshold, the WSD DS/NP starts redirecting clients to the remote servers and to other WSD DS/NP devices in distributed locations.

    Capacity Threshold (WSD DS/NP only):

    This is relevant to a WSD which is part of a distributed environment, where traffic is redirected to it by other WSD devices. When the capacity threshold is met, the WSD reports to remote WSD devices that it is no longer accepting further distributed sessions. However, all traffic reaching the VIP of this farm is directly served by this WSD.

    Redirection Mode:

    WSD DS/NP only. Defines the redirection method:

    HTTP Redirection: The WSD DS/NP uses HTTP redirection for sending HTTP sessions to remote sites. Other sessions (not HTTP) will be handled by the local servers only.

    Triangle Redirection (Not available on WSD Pro): All clients (including HTTP) are redirected by the triangulation method.

    HTTP & Triangle Redirection (Not available on WSD Pro): HTTP sessions are redirected by the HTTP redirection. All other sessions are redirected by the triangulation method.

    DNS Redirection: The WSD can operate as a DNS redirection, as well as a session redirection. If the WSD is defined as the farm's authoritative DNS, and DNS redirection is enabled, then the dispatching decision takes place in the DNS resolution stage and the reply is for the distributed site address. This mode is more efficient, because only one request comes to the WSD. On the other hand, when using proximity, it is possible that the requesting host (the server that will also receive the redirection) is not the client, but just one of the DNS servers on the network: thus the redirection will always be to the closest server on the network, but not always to the server closest to the client.

    DNS & HTTP & Triangle Redirection (Not available on WSD Pro): DNS redirection is used for DNS sessions, HTTP redirection used for HTTP sessions, and Triangle redirection is used for all other sessions.

    No Redirection: WSD does not redirect clients of this farm to any of remote or distributed servers. This also disables the dynamic proximity mechanism for the farm.

    RTSP Redirection: WSD forwards an RTSP request to a remote server or WSD, by responding with a standard RTSP redirection message causing the requesting client to establish a new connection to a remote site in order to view/hear streaming information. RTSP redirection can be used globally, redirecting clients to remote farms or servers, or locally, using Redirect to Self. RTSP Redirection preserves client-server persistency of RTSP sessions when Sessions Mode Select Server When Source Port is Different is used

     

    Static Persistency ID (WSD version WSD 8.00.02 or higher when using Static Persistency license):

    This string identifies the Session ID according to which server persistency is kept for this farm. Entering a key enables the Static Session ID mechanism.

    Redundancy Mode:

    For redundancy operation:

    Regular: The farm is operating regularly on this WSD device.

    Backup: The farm is not operational, and it backups another farm on another WSD device. When the other WSD fails, this farm takes over and becomes operational.

    Extended Check Frequency:

    To save unnecessary web page requests, web page retrieval can be performed only periodically. Only once in a number of requests, according to the retrieval frequency, the web page is requested. Otherwise, a simple TCP check for port 80 will occur.

    Look for Session IDs in URL (WSD version WSD 8.00.02 or higher when using Static Persistency license):

    When enabled, WSD examines the URL parameters of a client's request and selects servers based on those parameters. Session ID values configured in the Static Session ID Persistency Table are examined when this feature is enabled.

    Home Page:

    When choosing the "HTTP pages" check method, this field defines the default web page which will be retrieved from the servers. If this web page is unavailable, the server is considered down.

    Sessions Mode:

    The method used to handle new sessions:

    Regular: Each client that connects to the farm represents one entry in the Client Table, regardless of the number of sessions that client has.

    Entry Per Session: Each session a client opens is recorded in the client table. This provides more accurate minimum-user load balancing.  

    Server Per Session: Different sessions opened by a client's application will be served by different servers, according to the load balancing algorithms. This option enhances load balancing performance but may hinder some applications that depend on being served by the same server. It also may overload the WSD's internal tables.

    Remove on Session End: After a TCP client session ends, the next time that the device scans the Client Table (between 5 - 60 seconds) the client's entry is removed from the Client Table. This option automatically enables Entry Per Session.

    Remove Entry in Select Server: After a TCP client session ends, the next time that the device scans the Client Table (between 5 - 60 seconds) the client's entry is immediately removed from the Client Table. This option automatically enables Server Per Session.

    DNS Redirection Fallback:

    In WSD DS/NP only. If you configure the redirection mode to DNS Redirection, and there are no local servers available, you can configure a fallback redirection mode for non-DNS sessions.

    HTTP Redirection: WSD uses HTTP redirection for sending HTTP sessions to remote sites. Other sessions (not HTTP or DNS) will be discarded.

    Triangulation (Not available on WSD Pro): All clients (including HTTP) are redirected by the triangulation method.

    HTTP Redirection & Triangulation (Not available on WSD Pro): HTTP sessions are redirected by the HTTP redirection. All other sessions are redirected by the triangulation method.

    DNS Only:

     

    HTTP Redirection Mode:

    The WSD DS/NP uses HTTP redirection for sending HTTP sessions to remote sites in two ways:

    IP Mode: This mode redirects HTTP sessions to an IP address.

    Name Mode: This mode redirects HTTP sessions to an URL address, for example, www.radware.com.   

     

    Bandwidth Limit:

    The dropdown list enables you to specify the bandwidth limit for the farm.

    Authorized Username:

    Used for password protected HTTP page checks.

    Authorized Password:

    Used for password protected HTTP page checks.

  1. Click Create. The Farm Create window is displayed.

  2. Define the parameters according to the explanations above.

  3. Click Set. The farm is added to the list.