On SEAPATH, the virtual machines can migrate on the different hypervisors. If there is a need for two VMs to communicate with each other, a standard Linux bridge cannot be used because the location of both VMs on the cluster can change.

The solution is then to use an extended bridge over the cluster using OpenvSwitch and VXLAN. This bridge will use the physical cluster network and will be accessible no matter the position of the VMs on the cluster.

Extended bridge deployment

The deployment of the bridge is as follow:

The bridge to deploy is first described as an Ansible inventory.
This inventory is transformed into a configuration file through the role network_configovs.
This configuration file is copied on the SEAPATH machines in /etc/ovs_configuration.json
This configuration file is read by the seapath-config_ovs systemd service at each boot.
This service calls python3-setup-ovs, which launches the Open vSwitch commands.

The extended bridge is only deployed on the hypervisors, as the observer doesn’t run any virtual machines.

Deploy the bridge using Ansible

Below is an example inventory to deploy an extended bridge over the cluster. This inventory

Creates a brBRIDGE1 bridge
Configure VXLAN interfaces on this bridge to communicate with the other hypervisors on the cluster
Configure RSTP on this bridge to avoid a network loop
Configure two tap interfaces for VMs on this bridge

This example showcases only two standard tap interfaces for virtual machines. It is possible to add more interfaces, use VLAN features, use DPDK, or link this bridge to physical interfaces, so that it is accessible from outside the cluster. See the network_configovs role for details.

cluster_machines:
  children:
    hypervisors:
      vars:
        ovs_bridges:
          - name: brBRIDGE1
            rstp_enable: true
            other_config: "rstp-priority={{ br_rstp_priority | default(16384) }}"
            ports:
              - name: "brBRIDGE1_next"
                type: vxlan
                key: "1001"
                remote_ip: "{{ cluster_next_ip_addr }}"
              - name: "brBRIDGE1_previous"
                type: vxlan
                key: "1001"
                remote_ip: "{{ cluster_previous_ip_addr }}"
              - name: VM1.0
                type: tap
              - name: VM2.0
                type: tap

This inventory can be merged with the cluster inventory or handled as a separate inventory.
In any case, it should always be used along with the cluster one, as it uses some Ansible variables defined in there (RSTP priority and cluster IP)

This bridge can be deployed using the seapath_setup_network.yaml playbook.

Connect the virtual machine on this bridge

The VM can then be connected on the bridge using the templated guest.xml.j2 libvirt XML file.

vm:
  vm_template: "../templates/vm/guest.xml.j2"
  vm_disk: <your_vm_disk_path>
  ovs:
    - mac_address: "52:54:00:e4:ff:02"
      ovs_port: VM1.0

For more information on VM deployment and inventories, see Connect a virtual machine to the network

Create an extended bridge over the cluster

Extended bridge deployment

Deploy the bridge using Ansible

Connect the virtual machine on this bridge