"In-place updates change this. Depending on the nature of the change, Cluster API can now decide to modify an existing Machine on the spot without replacing it. This is particularly relevant for modifications that do not require a restart of Pods. Examples include changing credentials or configuration that does not directly impact running workloads. Both KubeadmControlPlane and MachineDeployments support this new capability through so-called update extensions. This shifts the boundary between immutable and mutable infrastructure."
"Cluster API is used by many platform teams to define the desired state of clusters, after which controllers automatically ensure that the infrastructure is brought into line with this. Until now, a change in the Machine specification almost always meant a so-called immutable rollout. This involved creating a new Machine and removing the old one. This approach is predictable and robust, but inevitably leads to node drains and the rearrangement of workloads."
"The second major innovation is chained upgrades. Organizations that offer Kubernetes-as-a-Service or manage multiple clusters often lag behind with minor releases. Until now, upgrades had to be performed step by step, with each intermediate version having to be explicitly run through. In version 1.12, an administrator can directly specify a target version, after which Cluster API automatically draws up and executes an upgrade plan."
Cluster API version 1.12 introduces in-place updates and chained upgrades to simplify Kubernetes cluster management. Previously, Machine spec changes triggered immutable rollouts that created a new Machine and removed the old one, causing node drains and workload rearrangement. In-place updates allow controllers to modify existing Machines when changes do not require Pod restarts, such as credential or non-disruptive configuration changes; KubeadmControlPlane and MachineDeployments support this via update extensions. Chained upgrades let administrators specify a final Kubernetes target version and have Cluster API automatically plan and execute all required intermediate upgrade steps in the correct order.
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