Today, traditional OS SKU migration involves creating a new node, cordoning and draining existing nodes, and then deleting existing nodes. This can involve a large surge of new nodes and operational overhead to cordon and drain existing nodepools.
The OS SKU in-place migration feature, now GA, allows you to trigger a node image upgrade between one Linux SKU (i.e. Ubuntu) to another (i.e. Azure Linux) on an existing nodepool.
Learn more.