PolyServe Understudy 1.3

4. Adding, Deleting and Updating Virtual Hosts

4.1 Adding a Virtual Host to a Cluster

To add a virtual host to the cluster, choose the Add Virtual Host option from the Cluster menu. Understudy will then open an Add a Virtual Host dialog box. Enter the IP address or name of the virtual host you wish to protect in the Virtual Host field. Then you will need to choose which cluster server should be primary for that virtual host, and which server would be backup, by clicking on the corresponding check buttons. Finally, you need to click on the OK button to authorize, or Cancel to cancel.
Note:
The server you choose to be primary for the new virtual host is the one to which requests will be routed in the normal case, i.e., when there are no failures.

Note:
Adding a virtual host will automatically configure its IP address on the corresponding cluster servers. There is no need to configure that IP address with other network utilities. In particular, DO NOT configure this IP address in the setup files of your web server.

Note:
Understudy does not take care of merging updates that were received at the backup server with those that were received at the primary, or of maintaining shared session variables. This can be done by using external software.

4.2 Deleting a Virtual Host from a Cluster

To delete a virtual host from the cluster, first select the virtual host you wish to delete by pointing the mouse on it and clicking on the mouse left button. After the virtual host is selected, choose Delete Selected Virtual Host from the Cluster menu. Understudy will then open an authorization dialog box. Click yes if you wish to authorize the operation, or no if you wish to cancel.
Note:
Deleting a virtual host will delete it and the corresponding IP address from all servers in the cluster. In this version of Understudy, a virtual host cannot be deleted from just one server.

4.3 Updating a Virtual Host in a Cluster

To update a virtual host, first select the virtual host you wish to update by pointing the mouse on it and clicking on the mouse left button. After the virtual host is selected, choose Update Selected Virtual Host from the Cluster menu. Understudy will then open a dialog box in which you can pick which cluster server should be primary for that virtual host, and which should be backup. Clicking on the corresponding check button to activate the desired configuration, and then click OK to authorize, or Cancel to cancel.
Note:
If you wish to bring down a server for scheduled maintenance, it is advisable (but not necessary) to first configure the cluster so that this server is a backup for all virtual hosts. This can be done by updating all configured virtual hosts before taking the server down. Doing so will save the failure detection time (approximately 10 seconds), and will ensure that your clients receive seamless service from your web server.