## High Availability Load Balancing High Availability Load Balancing (HALB) is a software layer that sits between the user and RAS Secure Client Gateways. Multiple HALB appliances can run simultaneously, one acting as the master and others as slaves. The higher the number of HALB appliances available, the lower the probability that users will experience downtime. Master and slave appliances share a common or virtual IP address (also known as VIP or VIPA). Should the master HALB appliance fail, a slave is promoted to master and takes its place seamlessly without affecting the end user connection. A HALB setup is per site, which means that you need at least one HALB for each site. Since HALB is a single point of contact for the client software, it is recommended to have at least two HALB appliances per site for redundancy. Setting up High Availability Load Balancing is a 2 stage process: Installing a HALB appliance. Configuring the HALB appliance in the RAS console. Hypervisor Prerequisites Before configuring HALB in the RAS console, first import a HALB appliance to either of the following Hypervisor platforms: Microsoft Hyper-V, Virtual Box or VMware. An appliance is a pre-configured virtual machine with the operating system installed and all relevant settings configured. Virtualbox/VMware For Virtual Box or VMware, this appliance should be imported with either the OVA or zipped VMDK appliance file obtained from the following locations: VMDK: `http://download.parallels.com/ras/v15/RAS_VDI_Appliance.vmdk.zip` OVA: `http://download.parallels.com/ras/v15/RAS_VDI_Appliance.ova` If deployed via the OVA file, the VM is applied with machine specifications already configured. Alternatively deployment via the VMDK file deploys the VM without pre-configured specifications. The minimum specifications for this VM are outlined below: 1 CPU 256 mb RAM 1 Network Card Microsoft Hyper-V For Microsoft Hyper-V this appliance should be imported with the VHD file obtained from this location: `http://download.parallels.com/ras/v15/RAS_HALB_Appliance.vhd.zip` Installing a HALB Appliance The HALB appliance should be imported on a hypervisor running on a separate machine connected to the same local network as Parallels RAS. Import the HALB appliance on a supported hypervisor using the following step: Import the HALB appliance file in the virtualization platform’s management console. Power up (boot) the new appliance to display the HALB - First boot configuration screen. Adjust the network settings (if necessary) and click Apply to continue. The Configuration Console is displayed and the HALB appliance is ready to be added to a RAS farm. Note: Repeat the process above to create multiple HALB appliances.