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Configuration Patches

In this guide, we’ll patch the generated machine configuration.

Talos generates machine configuration for two types of machines: controlplane and worker machines. Many configuration options can be adjusted using talosctl gen config but not all of them. Configuration patching allows modifying machine configuration to fit it for the cluster or a specific machine.

Configuration Patch Formats

Talos supports two configuration patch formats:

  • strategic merge patches
  • RFC6902 (JSON patches)

Strategic merge patches are the easiest to use, but JSON patches allow more precise configuration adjustments.

Note: Talos 1.5+ supports multi-document machine configuration. JSON patches don’t support multi-document machine configuration, while strategic merge patches do.

Strategic Merge patches

Strategic merge patches look like incomplete machine configuration files:

machine:
  network:
    hostname: worker1

When applied to the machine configuration, the patch gets merged with the respective section of the machine configuration:

machine:
  network:
    interfaces:
      - interface: eth0
        addresses:
          - 10.0.0.2/24
    hostname: worker1

In general, machine configuration contents are merged with the contents of the strategic merge patch, with strategic merge patch values overriding machine configuration values. There are some special rules:

  • If the field value is a list, the patch value is appended to the list, with the following exceptions:
    • values of the fields cluster.network.podSubnets and cluster.network.serviceSubnets are overwritten on merge
    • network.interfaces section is merged with the value in the machine config if there is a match on interface: or deviceSelector: keys
    • network.interfaces.vlans section is merged with the value in the machine config if there is a match on the vlanId: key
    • cluster.apiServer.auditPolicy value is replaced on merge

When patching a multi-document machine configuration, following rules apply:

  • for each document in the patch, the document is merged with the respective document in the machine configuration (matching by kind, apiVersion and name for named documents)
  • if the patch document doesn’t exist in the machine configuration, it is appended to the machine configuration

The strategic merge patch itself might be a multi-document YAML, and each document will be applied as a patch to the base machine configuration.

RFC6902 (JSON Patches)

JSON patches can be written either in JSON or YAML format. A proper JSON patch requires an op field that depends on the machine configuration contents: whether the path already exists or not.

For example, the strategic merge patch from the previous section can be written either as:

- op: replace
  path: /machine/network/hostname
  value: worker1

or:

- op: add
  path: /machine/network/hostname
  value: worker1

The correct op depends on whether the /machine/network/hostname section exists already in the machine config or not.

Examples

Machine Network

Base machine configuration:

# ...
machine:
  network:
    interfaces:
      - interface: eth0
        dhcp: false
        addresses:
          - 192.168.10.3/24

The goal is to add a virtual IP 192.168.10.50 to the eth0 interface and add another interface eth1 with DHCP enabled.

machine:
  network:
    interfaces:
      - interface: eth0
        vip:
          ip: 192.168.10.50
      - interface: eth1
        dhcp: true
- op: add
  path: /machine/network/interfaces/0/vip
  value:
    ip: 192.168.10.50
- op: add
  path: /machine/network/interfaces/-
  value:
    interface: eth1
    dhcp: true

Patched machine configuration:

machine:
  network:
    interfaces:
      - interface: eth0
        dhcp: false
        addresses:
          - 192.168.10.3/24
        vip:
          ip: 192.168.10.50
      - interface: eth1
        dhcp: true

Cluster Network

Base machine configuration:

cluster:
  network:
    dnsDomain: cluster.local
    podSubnets:
      - 10.244.0.0/16
    serviceSubnets:
      - 10.96.0.0/12

The goal is to update pod and service subnets and disable default CNI (Flannel).

cluster:
  network:
    podSubnets:
      - 192.168.0.0/16
    serviceSubnets:
      - 192.0.0.0/12
    cni:
      name: none
- op: replace
  path: /cluster/network/podSubnets
  value:
    - 192.168.0.0/16
- op: replace
  path: /cluster/network/serviceSubnets
  value:
    - 192.0.0.0/12
- op: add
  path: /cluster/network/cni
  value:
    name: none

Patched machine configuration:

cluster:
  network:
    dnsDomain: cluster.local
    podSubnets:
      - 192.168.0.0/16
    serviceSubnets:
      - 192.0.0.0/12
    cni:
      name: none

Kubelet

Base machine configuration:

# ...
machine:
  kubelet: {}

The goal is to set the kubelet node IP to come from the subnet 192.168.10.0/24.

machine:
  kubelet:
    nodeIP:
      validSubnets:
        - 192.168.10.0/24
- op: add
  path: /machine/kubelet/nodeIP
  value:
    validSubnets:
      - 192.168.10.0/24

Patched machine configuration:

machine:
  kubelet:
    nodeIP:
      validSubnets:
        - 192.168.10.0/24

Admission Control: Pod Security Policy

Base machine configuration:

cluster:
  apiServer:
    admissionControl:
      - name: PodSecurity
        configuration:
          apiVersion: pod-security.admission.config.k8s.io/v1alpha1
          defaults:
            audit: restricted
            audit-version: latest
            enforce: baseline
            enforce-version: latest
            warn: restricted
            warn-version: latest
          exemptions:
            namespaces:
              - kube-system
            runtimeClasses: []
            usernames: []
          kind: PodSecurityConfiguration

The goal is to add an exemption for the namespace rook-ceph.

cluster:
  apiServer:
    admissionControl:
      - name: PodSecurity
        configuration:
          exemptions:
            namespaces:
              - rook-ceph
- op: add
  path: /cluster/apiServer/admissionControl/0/configuration/exemptions/namespaces/-
  value: rook-ceph

Patched machine configuration:

cluster:
  apiServer:
    admissionControl:
      - name: PodSecurity
        configuration:
          apiVersion: pod-security.admission.config.k8s.io/v1alpha1
          defaults:
            audit: restricted
            audit-version: latest
            enforce: baseline
            enforce-version: latest
            warn: restricted
            warn-version: latest
          exemptions:
            namespaces:
              - kube-system
              - rook-ceph
            runtimeClasses: []
            usernames: []
          kind: PodSecurityConfiguration

Configuration Patching with talosctl CLI

Several talosctl commands accept config patches as command-line flags. Config patches might be passed either as an inline value or as a reference to a file with @file.patch syntax:

talosctl ... --patch '[{"op": "add", "path": "/machine/network/hostname", "value": "worker1"}]' --patch @file.patch

If multiple config patches are specified, they are applied in the order of appearance. The format of the patch (JSON patch or strategic merge patch) is detected automatically.

Talos machine configuration can be patched at the moment of generation with talosctl gen config:

talosctl gen config test-cluster https://172.20.0.1:6443 --config-patch @all.yaml --config-patch-control-plane @cp.yaml --config-patch-worker @worker.yaml

Generated machine configuration can also be patched after the fact with talosctl machineconfig patch

talosctl machineconfig patch worker.yaml --patch @patch.yaml -o worker1.yaml

Machine configuration on the running Talos node can be patched with talosctl patch:

talosctl patch mc --nodes 172.20.0.2 --patch @patch.yaml
Last modified December 8, 2023: docs: provide documentation for Talos 1.6 (d803e40ef)