When you create a virtual machine you need to select a cluster node where that machine will be located.

You can select a cluster node from a list of the existing ones or it can be selected automatically (by default).

This article describes the automatic selection of a cluster node. 

  1. VMmanager generates a list of cluster nodes and sorts it out based on the number of virtual machines created on the cluster.
  2. The system checks that every cluster node meets specific requirements:
    1. its status;
    2. the maximum number of virtual machines created on the node;
    3. error notifications on the cluster node;
    4. available resources and overselling:
      1. Calculates the available amount of RAM.
      2. Checks that there is enough RAM to install the virtual machine without overselling.

      3. Calculates the amount of RAM including overselling M: M = T * O ÷ 100.

        T — total amount of RAM;

        O — overselling value. 

      4. Checks that there is enough RAM to install the virtual machine with overselling.
      5. Checks that there is enough disk space to install the virtual machine.
  3. The new virtual machine will be created on the first node that meets all the requirements. If no cluster nodes meet the requirements, the virtual machine will not be created.

Cluster node status

There are 2 statuses: "Blocked" and "Unblocked". Virtual machines can be created on a cluster node depending on its status. A blocked cluster node will be excluded from the list.

You can block a node in the Cluster settings→ Cluster nodes. Alternatively, you can add the CreateVmDisableNodeTimer parameter into the VMmanager configuration file (the default location is /usr/local/mgr5/etc/vmmgr.conf). This parameter specifies a period in minutes when a cluster node will be excluded from the list of nodes where virtual machines can be created automatically. After you add the parameter, the cluster node will be blocked for a specified period after a virtual machine is created. If the virtual machine is installed before that period, the node will get unblocked.

Maximum number of virtual machines

When creating a cluster node, you can specify the Maximum number of VM (unlimited by default), which defines the number of machines that can run simultaneously on a cluster node. The check will be passed successfully if the maximum number is not reached.

Error notifications

The check is passed successfully if the cluster node is up and running.

Available resources and overselling

The system checks available resources on a cluster node taking into account the amount of overselling. Learn more in Policy settings. The check is passed successfully if there is at least 10% of each resource (RAM, HDD, CPU) for creating a new virtual machine.