Machine Controller
The Machine controller is responsible for reconciling the Machine resource.
In order to allow Machine provisioning on different type of infrastructure, The Machine resource references an InfraMachine object, e.g. AWSMachine, GCMachine etc.
The InfraMachine resource contract defines a set of rules a provider is expected to comply with in order to allow the expected interactions with the Machine controller.
Among those rules:
- InfraMachine MUST report a provider ID for the Machine
- InfraMachine SHOULD take into account the failure domain where machines should be placed in
- InfraMachine SHOULD surface machine’s addresses to help operators when troubleshooting issues
- InfraMachine MUST report when Machine’s infrastructure is fully provisioned
- InfraMachine SHOULD report conditions
- InfraMachine SHOULD report terminal failures
Similarly, in order to support different machine bootstrappers, The Machine resource references a BootstrapConfig object, e.g. KubeadmBoostrapConfig etc.
The BootstrapConfig resource contract defines a set of rules a provider is expected to comply with in order to allow the expected interactions with the Machine controller.
Among those rules:
- BootstrapConfig MUST create a bootstrap data secret where machines should be placed in
- BootstrapConfig MUST report when Machine’s bootstrap data secret is fully provisioned
- BootstrapConfig SHOULD report conditions
- BootstrapConfig SHOULD report terminal failures
- BootstrapConfig SHOULD report taint Nodes at creation
- BootstrapConfig SHOULD create a sentinel file on machines
Considering all the info above, the Machine controller’s main responsibilities are:
- Setting an OwnerReference on the infrastructure object referenced in
Machine.spec.infrastructureRef. - Setting an OwnerReference on the bootstrap object referenced in
Machine.spec.bootstrap.configRef. - Keeping the Machine’s status in sync with the InfraMachine and BootstrapConfig’s status.
- Finding Kubernetes nodes matching the expected providerID in the workload cluster.
- Setting NodeRefs to be able to associate machines and Kubernetes nodes.
- Monitor Kubernetes nodes and propagate labels to them.
- Cleanup of all owned objects so that nothing is dangling after deletion.
- Drain nodes and wait for volumes being detached by CSI plugins.
After the machine controller sets the OwnerReferences on the associated objects, it waits for the bootstrap
and infrastructure objects referenced by the machine to have the Status.Ready field set to true. When
the infrastructure object is ready, the machine controller will attempt to read its Spec.ProviderID and
copy it into Machine.Spec.ProviderID.
The machine controller uses the kubeconfig for the new workload cluster to watch new nodes coming up.
When a node appears with Node.Spec.ProviderID matching Machine.Spec.ProviderID, the machine controller
transitions the associated machine into the Provisioned state. When the infrastructure ref is also
Ready, the machine controller marks the machine as Running.
The following schema goes through machine phases and interactions with InfraMachine and BootstrapConfig happening at each step.
