The vSphere Clustering Service (vCLS) is a new capability that is introduced in the vSphere 7 Update 1 release. It’s first release provides the foundation to work towards creating a decoupled and distributed control plane for clustering services in vSphere.
Starting with vSphere 7.0 Update 1, vSphere Cluster Services (vCLS) is enabled by default and runs in all vSphere clusters. vCLS ensures that if vCenter Server becomes unavailable, cluster services remain available to maintain the resources and health of the workloads that run in the clusters. vCenter Server is still required in 7.0 update 1 to run DRS and HA.
vCLS uses agent virtual machines to maintain cluster services health. The vCLS agent virtual machines (vCLS VMs) are created when you add hosts to clusters. Up to three vCLS VMs are required to run in each vSphere cluster, distributed within a cluster. vCLS is also enabled on clusters which contain only one or two hosts. In these clusters the number of vCLS VMs is one and two.
In vSphere 6 we can use various methods and tools to deploy ESXi hosts and maintain their software lifecycle.
To deploy and boot an ESXi host, you can use an ESXi installer image or VMware vSphere® Auto Deploy™. The availability of choice options results in two different underlying ESXi platforms:
Using vSphere Auto Deploy – stateless mode
Using an installer ESXi image – statefull mode
vSphere Lifecycle Manager Images: A Single Platform, Single Tool, Single Workflow
By introducing the concept of images, vSphere Lifecycle Manager provides a unified platform for ESXi lifecycle management. You can use vSphere Lifecycle Manager for stateful hosts only, but starting with vSphere 7.0, you can convert the Auto Deploy-based stateless hosts into stateful hosts, which you can add to clusters that you manage with vSphere Lifecycle Manager images.
How to Upgrade ESXi 6.7 to 7 with vSphere Lifecycle Manager?
After upgrade VCSA 7.0, We prepare upgrade for ESXi 6.7. It is simular logic like in vSphere Update Manager: