Service Control

Service control refers to the ability to specify which OVN services run on any given node in the cluster. The list of services can be found here Services Reference and they are responsible for handling core functionality.

The services of the each cluster node can be specified either during the initialisation of the node, or after the deployment via MicroOVN’s CLI.

The approach of using snap CLI to enable/disable services is not recommended, because it does not update the desired state or handle joining clusters and configuring the service properly.

Change services on a deployed cluster

MicroOVN offers disable and enabled subcommands that can change which services are active on the current cluster node.

Note

This assumes you have MicroOVN installed and a clustered across three of more nodes. These nodes will be referred to as first, second and third respectively.

Disable a MicroOVN service

Disabling a MicroOVN service will configure it to not start automatically at boot and stop the service if it is running.

run on first:

microovn disable switch

Service switch disabled

To validate that this has worked, we can query the status of MicroOVN and check which services are enabled. We should find that all nodes have central, chassis and switch, except first having only central and chassis. This shows the disabling worked

run on first:

microovn status

MicroOVN deployment summary:
- first (10.190.155.5)
Services: central, chassis
- second (10.190.155.174)
Services: central, chassis, switch
- third (10.190.155.55)
Services: central, chassis, switch
OVN Database summary:
OVN Northbound: OK (7.3.0)
OVN Southbound: OK (20.33.0)

The other nodes have also been informed of this change to the service placement and when queried will confirm that switch is disabled on first from their perspective too.

run on second:

microovn status

MicroOVN deployment summary:
- first (10.190.155.5)
Services: central, chassis
- second (10.190.155.174)
Services: central, chassis, switch
- third (10.190.155.55)
Services: central, chassis, switch
OVN Database summary:
OVN Northbound: OK (7.3.0)
OVN Southbound: OK (20.33.0)

Enable a MicroOVN service

Enabling a MicroOVN service will configure it to start automatically at boot and if the service is not running, start it.

run on first:

microovn enable switch

Service switch enabled

Note

If the switch service is enabled you may get an error, this is fine.

This will enable the switch service in MicroOVN, This can be shown through the listing of system services owned by MicroOVN. As mentioned in the disable section, these do not always translate directly to a MicroOVN service, but in this case it does.

run on first:

microovn status

MicroOVN deployment summary:
- first (10.190.155.5)
Services: central, chassis, switch
- second (10.190.155.174)
Services: central, chassis, switch
- third (10.190.155.55)
Services: central, chassis, switch
OVN Database summary:
OVN Northbound: OK (7.3.0)
OVN Southbound: OK (20.33.0)

You should be able to see here that the service is running and enabled on startup. The other nodes are also aware of this as if you query the status you will see it there and running.

run on second:

microovn status

MicroOVN deployment summary:
- first (10.190.155.5)
Services: central, chassis, switch
- second (10.190.155.174)
Services: central, chassis, switch
- third (10.190.155.55)
Services: central, chassis, switch
OVN Database summary:
OVN Northbound: OK (7.3.0)
OVN Southbound: OK (20.33.0)

Uses

Typically the most common use case of this will be to control the nodes the central services are running on and to increase the number of central services beyond the default of 3.

Specify services during the cluster deployment

The default selection of services for the node can be adjusted via the interactive microovn init command during the deployment (instead of using bootstrap and join methods). The user is asked question:

Please select comma-separated list services you would like to enable on this node (central/chassis/switch) or let MicroOVN automatically decide (auto) [default=auto]:

Here, they can either define the desired services as a comma-separated string or select auto option which falls back to the default behaviour. Leaving this option empty has same effect as selecting auto.

Note

The default behaviour for selecting services is to always enable switch and chassis services. The central service is enabled only if configuration option ovn.central-ips is not set and there are less than 3 nodes with central service enabled in the cluster.