Node Selection for Data Movement Backup

Velero node-agent is a daemonset hosting the data movement modules to complete the concrete work of backups/restores.
Varying from the data size, data complexity, resource availability, the data movement may take a long time and remarkable resources (CPU, memory, network bandwidth, etc.) during the backup and restore.

Velero data movement backup supports to constrain the nodes where it runs. This is helpful in below scenarios:

• Prevent the data movement backup from running in specific nodes because users have more critical workloads in the nodes
• Constrain the data movement backup to run in specific nodes because these nodes have more resources than others
• Constrain the data movement backup to run in specific nodes because the storage allows volume/snapshot provisions in these nodes only

Velero introduces a new section in node-agent-config configMap, called loadAffinity, through which you can specify the nodes to/not to run data movement backups, in the affinity and anti-affinity flavors.
If it is not there, node-agent-config should be created manually. The configMap should be in the same namespace where Velero is installed. If multiple Velero instances are installed in different namespaces, there should be one configMap in each namespace which applies to node-agent in that namespace only.
Node-agent server checks these configurations at startup time. Therefore, you could edit this configMap any time, but in order to make the changes effective, node-agent server needs to be restarted.

Sample

Here is a sample of the node-agent-config configMap with loadAffinity:

{
    "loadAffinity": [
        {
            "nodeSelector": {
                "matchLabels": {
                    "beta.kubernetes.io/instance-type": "Standard_B4ms"
                },
                "matchExpressions": [
                    {
                        "key": "kubernetes.io/hostname",
                        "values": [
                            "node-1",
                            "node-2",
                            "node-3"
                        ],
                        "operator": "In"
                    },
                    {
                        "key": "xxx/critial-workload",
                        "operator": "DoesNotExist"
                    }
                ]          
            }
        }
    ]
}

To create the configMap, save something like the above sample to a json file and then run below command:

kubectl create cm node-agent-config -n velero --from-file=<json file name>

Affinity

Affinity configuration means allowing the data movement backup to run in the nodes specified. There are two ways to define it:

• It could be defined by MatchLabels. The labels defined in MatchLabels means a LabelSelectorOpIn operation by default, so in the current context, they will be treated as affinity rules. In the above sample, it defines to run data movement backups in nodes with label beta.kubernetes.io/instance-type of value Standard_B4ms (Run data movement backups in Standard_B4ms nodes only).
• It could be defined by MatchExpressions. The labels are defined in Key and Values of MatchExpressions and the Operator should be defined as LabelSelectorOpIn or LabelSelectorOpExists. In the above sample, it defines to run data movement backups in nodes with label kubernetes.io/hostname of values node-1, node-2 and node-3 (Run data movement backups in node-1, node-2 and node-3 only).

Anti-affinity

Anti-affinity configuration means preventing the data movement backup from running in the nodes specified. Below is the way to define it:

• It could be defined by MatchExpressions. The labels are defined in Key and Values of MatchExpressions and the Operator should be defined as LabelSelectorOpNotIn or LabelSelectorOpDoesNotExist. In the above sample, it disallows data movement backups to run in nodes with label xxx/critial-workload.