Resource based & round robin load balancing

Load Balancer in Parallels RAS is designed to balance RD Session Host connections from Parallels Clients.

The following types of load balancing are available:

  • Resource based. Distributes sessions to servers depending on how busy the servers are. A new incoming session is always redirected to the least busy server.
  • Round robin. Redirects sessions in sequential order. For example, let's say there are two RD Session Hosts in the Farm. The first session is redirected to server 1, the second session is redirected to server 2, and the third session is redirected to server 1 again.

Both methods are explained in this and the following subsections. Load Balancing options can be configured from the Load Balancing category in the RAS Console.

Selecting load balancing method

Load balancing is enabled by default when more than one server is available in a Site. The resource based load balancing is the default method. Load balancing method can be selected from the Method drop-down list.

Configuring resource counters

Resource-based load balancing uses the following counters to determine if a given server is busier than other servers and vice versa:

  • User sessions: Redirect users to a server with the least number of sessions.
  • Memory: Redirect users to the server with the best free/used RAM ratio.
  • CPU: Redirect users to the server with the best free/used CPU time ratio.

When all of the counters are enabled, the Load Balancer adds the counter ratios together and redirects the session to the server with the most favorable combined ratio.

To remove a counter from the equation, clear the checkbox next to the counter name in the Counters section.

Session options

Reconnect to disconnected sessions: Enable this option to redirect incoming user sessions to a previously disconnected session owned by the same user.

Reconnect sessions using client’s IP address only: When reconnecting to a disconnected session, the Parallels RAS will match the username requesting reconnection with the username of the disconnected session to match the sessions. With this option enabled, Parallels RAS will determine to which disconnected session to reconnect the session by matching the source IP address.

Limit each user to one session per desktop: Enable this option to ensure that the same user does not open multiple sessions. Please note that for this option to work, your session host must also be configured to restrict each user to a single session. In Windows Server 2012(R2), it's the "Restrict Remote Desktop Services users to a single Remote Desktop Services session" option in Local Group Policy \ Remote Desktop Services \ Remote Desktop Session Host \ Connections.

Disable Microsoft RD Connection Broker: If this option is enabled, the Microsoft RD Connection Broker will not interfere with the RAS brokering done by the RAS Connection Broker if it is installed. Please note that this option will only work with Windows Server 2012 and above.

Agent timeout and refresh time

You can also change the default timeout and refresh time for RAS agents running on the servers. If you believe that it takes too long to wait for an agent to respond or if the timeout is not long enough, you can specify your own values.

To change default timeouts:

  1. Click the Configure button.
  2. In the dialog that opens, specify the time period in seconds in the Declare agent dead if not responding for field. If the agent is not responding within this time period, the server is excluded from the load balancer.
  3. In the Agent Refresh Time field, specify the number of seconds needed to check if the agent is reachable.
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