VMware ESXi Core Processes

vmware_esxiThere are not much information on VMware ESXi architecture out there. There is an old whitepaper “The Architecture of VMware ESXi” which dates back to 2007. In fact, from the management perspective there are only two OS processes critical two ESXi management. These are: hostd (vmware-hostd in ESXi 4) and vpxa (vmware-vpxa in ESXi 4) which are called “Management Agents”.

hostd process is a communication layer between vmkernel and the outside world. It invokes all management operations on VMs, storage, network, etc by directly talking to the OS kernel. If hostd dies you won’t be able to connect to the host neither from vCenter nor VI client. But you will still have an option to connect directly to the host console via SSH.

vpxa is an intermediate layer between vCenter and hostd and is called “vCenter Server Agent”. If you have communication failure between vCenter and ESXi host, it’s the first thing to blame.

Say you have a storage LUN failure and hostd can’t release the datastore. You can restart hostd or both of the processes using these scripts:

# vmware-hostd restart
# vmware-vpxa restart

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