Resource Based & Round Robin Load Balancing

The Parallels RAS Load Balancer distributes connections from Parallels Clients between RD Session Hosts in a Site. It supports the following load-balancing methods:

• Resource based: Directs a new session to the RD Session Host with the most favorable resource-load ratio.
• Round robin: Directs sessions to RD Session Hosts sequentially.

Load-balancing settings are configured in the Load Balancing category of the Parallels RAS Console.

Resource-based load balancing

Resource-based load balancing is enabled by default when more than one server is available in a Site. It is also the default load-balancing method.

To select resource-based load balancing:

1. Open the RAS Console.
2. Navigate to the Load Balancing category.
3. In the Method drop-down list, select Resource Based.
4. Click Apply or OK.

Resource counters

Resource-based load balancing uses the following counters to determine how busy each RD Session Host is:

• User sessions: Directs users to the server with the fewest sessions.
• Memory: Directs users to the server with the most favorable free-to-used RAM ratio.
• CPU: Directs users to the server with the most favorable free-to-used CPU-time ratio.

When multiple counters are enabled, the Load Balancer combines their ratios and directs the incoming session to the server with the most favorable combined result.

To exclude a counter from the load-balancing calculation, clear the checkbox next to the counter in the Counters section. Select the checkbox again to include the counter.

Round-robin load balancing

Round-robin load balancing directs sessions to RD Session Hosts in sequential order. For example, with two RD Session Hosts, the first session is directed to server 1, the second session to server 2, and the third session to server 1 again.

Enable round-robin load balancing

1. Open the RAS Console.
2. Navigate to the Load Balancing category.
3. In the Method drop-down list, select Round Robin.
4. Click Apply or OK.

Session options

The following options are available in the Load Balancing category.

Reconnect to disconnected sessions

Enable Reconnect to disconnected sessions to redirect an incoming user connection to a previously disconnected session owned by the same user.

Reconnect sessions using the client IP address only

When reconnecting to a disconnected session, Parallels RAS matches the username requesting the reconnection with the username of the disconnected session. When Reconnect sessions using client’s IP address only is enabled, Parallels RAS also uses the source IP address to select the disconnected session.

Use this option when users may have more than one disconnected session and the client IP address can reliably identify the correct session.

Limit each user to one session per desktop

Enable Limit each user to one session per desktop to prevent the same user from opening multiple sessions for the same published desktop.

For this option to work as intended, the RD Session Host must also be configured to restrict each user to a single Remote Desktop Services session. In Windows Server 2012 and later, configure the following Group Policy setting on the RD Session Host:

Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Connections > Restrict Remote Desktop Services users to a single Remote Desktop Services session

Disable Microsoft RD Connection Broker

Enable Disable Microsoft RD Connection Broker when Microsoft RD Connection Broker is installed and should not interfere with brokering performed by the Parallels RAS Connection Broker.

This option is supported with Windows Server 2012 and later.

Configure agent timeout and refresh time

You can configure how long Parallels RAS waits for a RAS Agent to respond and how frequently it checks whether the agent is reachable.

1. In the Load Balancing category, click Configure.
2. In Declare agent dead if not responding for, specify the timeout in seconds. If the agent does not respond within this period, its server is excluded from load balancing.
3. In Agent Refresh Time, specify the interval in seconds at which Parallels RAS checks whether the agent is reachable.
4. Click OK to save the changes.

Note: Use timeout and refresh values that reflect the network conditions and expected response time of the RAS Agents. A timeout that is too short may temporarily exclude a healthy server from load balancing.

Recommendations

• Use Resource Based load balancing when RD Session Hosts have different workloads or when the goal is to distribute sessions according to server utilization.
• Use Round Robin when sessions should be distributed sequentially without using the resource counters.
• Review the enabled resource counters when resource-based load balancing does not distribute sessions as expected.
• Verify that disconnected-session reconnection settings match the organization’s session-management requirements.