The VIRTUAL SERVERS panel displays information for each currently defined virtual server. Each table entry shows the status of the virtual server, the server name, the virtual IP assigned to the server, the netmask of the virtual IP, the port number to which the service communicates, the protocol used, and the virtual device interface.
Each server displayed in the VIRTUAL SERVERS panel can be configured on subsequent screens or subsections.
To add a service, click the ADD button. To remove a service, select it by clicking the radio button next to the virtual server and click the DELETE button.
To enable or disable a virtual server in the table click its radio button and click the (DE)ACTIVATE button.
After adding a virtual server, you can configure it by clicking the radio button to its left and clicking the EDIT button to display the VIRTUAL SERVER subsection.
The VIRTUAL SERVER subsection panel shown in Figure 1.34, “The VIRTUAL SERVERS Subsection” allows you to configure an individual virtual server. Links to subsections related specifically to this virtual server are located along the top of the page. But before configuring any of the subsections related to this virtual server, complete this page and click on the ACCEPT button.
- Name
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A descriptive name to identify the virtual server. This name is not the hostname for the machine, so make it descriptive and easily identifiable. You can even reference the protocol used by the virtual server, such as HTTP.
- Application port
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The port number through which the service application will listen.
- Protocol
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Provides a choice of UDP or TCP, in a drop-down menu.
- Virtual IP Address
- Virtual IP Network Mask
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The netmask for this virtual server, in the drop-down menu.
- Firewall Mark
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For entering a firewall mark integer value when bundling multi-port protocols or creating a multi-port virtual server for separate, but related protocols.
- Device
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The name of the network device to which you want the floating IP address defined in the Virtual IP Address field to bind.
You should alias the public floating IP address to the Ethernet interface connected to the public network.
- Re-entry Time
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An integer value that defines the number of seconds before the active LVS router attempts to use a real server after the real server failed.
- Service Timeout
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An integer value that defines the number of seconds before a real server is considered dead and not available.
- Quiesce server
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When the Quiesce server radio button is selected, anytime a new real server node comes online, the least-connections table is reset to zero so the active LVS router routes requests as if all the real servers were freshly added to the cluster. This option prevents the a new server from becoming bogged down with a high number of connections upon entering the cluster.
- Load monitoring tool
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The LVS router can monitor the load on the various real servers by using either rup or ruptime. If you select rup from the drop-down menu, each real server must run the rstatd service. If you select ruptime, each real server must run the rwhod service.
- Scheduling
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The preferred scheduling algorithm from the drop-down menu. The default is Weighted least-connection.
- Persistence
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Used if you need persistent connections to the virtual server during client transactions. Specifies the number of seconds of inactivity allowed to lapse before a connection times out in this text field.
- Persistence Network Mask
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To limit persistence to particular subnet, select the appropriate network mask from the drop-down menu.
Clicking on the REAL SERVER subsection link at the top of the panel displays the EDIT REAL SERVER subsection. It displays the status of the physical server hosts for a particular virtual service.
Click the ADD button to add a new server. To delete an existing server, select the radio button beside it and click the DELETE button. Click the EDIT button to load the EDIT REAL SERVER panel, as seen in Figure 1.36, “The REAL SERVER Configuration Panel”.
This panel consists of three entry fields:
- Name
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A descriptive name for the real server.
Tip
This name is not the hostname for the machine, so make it descriptive and easily identifiable.
- Address
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The real server's IP address. Since the listening port is already specified for the associated virtual server, do not add a port number.
- Weight
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An integer value indicating this host's capacity relative to that of other hosts in the pool. The value can be arbitrary, but treat it as a ratio in relation to other real servers.
Click on the MONITORING SCRIPTS link at the top of the page. The EDIT MONITORING SCRIPTS subsection allows the administrator to specify a send/expect string sequence to verify that the service for the virtual server is functional on each real server. It is also the place where the administrator can specify customized scripts to check services requiring dynamically changing data.
- Sending Program
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For more advanced service verification, you can use this field to specify the path to a service-checking script. This function is especially helpful for services that require dynamically changing data, such as HTTPS or SSL.
To use this function, you must write a script that returns a textual response, set it to be executable, and type the path to it in the Sending Program field.
Note
If an external program is entered in the Sending Program field, then the Send field is ignored.
- Send
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A string for the nanny daemon to send to each real server in this field. By default the send field is completed for HTTP. You can alter this value depending on your needs. If you leave this field blank, the nanny daemon attempts to open the port and assume the service is running if it succeeds.
Only one send sequence is allowed in this field, and it can only contain printable, ASCII characters as well as the following escape characters:
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\n for new line.
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\r for carriage return.
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\t for tab.
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\ to escape the next character which follows it.
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- Expect
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The textual response the server should return if it is functioning properly. If you wrote your own sending program, enter the response you told it to send if it was successful.