When I attended VMware ICM training in 2012, this was probably what I first learn in the class. This blog summarises my 'One-Pager', high level understanding of this topic, taking some references to VMware official training guide.
By definition, 'vCenter Server is a service that acts as a central administration point for ESXi hosts and their virtual machines connected on a network'. With VMware NSX (Specifically, NSX-V), it also leverages vCenter Server as it's administration portal.
There can be 2 flavours; Runs on Windows or on a Linux-based appliance.
It provides advanced features, such as vSphere DRS, vSphere HA, vSphere FT, vSphere vMotion, vSphere Storage vMotion.
With vCenter Server 6.5, it supports:
2,000 hosts per vCenter Server
25,000 Powered-on VMs per vCenter server
64 hosts per cluster
8,000 VMs per cluster
Enhanced Linked mode
vCenter Server group of services contains:
vSphere Web Client (server)
vSphere Update Manager (Disabled by default for appliance, required separate installation for Windows Server)
VMware vSphere Auto Deploy (Disabled by default)
VMware vSphere ESXi Dump Collector (Disabled by default for Windows Server)
VMware vSphere Syslog Collector (Disabled by default)
vRealize Orchestrator (Require separate installation)
ESXi and vCenter Server Communication
Below diagram is extracted from VMware official training material and I find it simple and easy to under ESXi and vCenter Server communication.
vCenter Server Appliance
VMware Photon OS 1.0
The Platform Services Controller group of infra services (For more info, refer to my VMware vSphere 6.5 PSC blog, or VMware KB article https://kb.vmware.com/s/article/2113115)
vCenter group of services
vCenter Server High Availability (VCHA)
Newly introduced in vSphere 6.5 and exclusively available only for vCenter Server Appliance, this has been a feature that has been requested by a number of my customers, although for most customer, they are fine without this function.
VCHA protects vCenter Server Appliance against host and hardware failures.
It is base on an active-passive architecture.
3 node cluster that contains Active, Passive and Witness nodes
Can help reduce downtime when patching vCenter Server Appliance.
Supports both internal or external PSC
Available in 'Basic' and 'Advanced' options
Native vCenter Server Appliance Backup and Restore
Backup key parts of the appliance (Both vCenter Server Appliance and PSC) using the native vCenter Server Appliance Management API.
Backup key files (such as vCenter Server database and system configuration files etc) into a tar bundle
File can be encrypted before transmission to the backup storage using a password which will also be used to decrypt the file during restoration.
Supports HTTP/S, SCP, FTP/S
Restores the vCenter Server instance to a brand new appliance
What happens when vCenter Server goes down?
One of the most common question asked by customers. A quick answer to this is, it will not affect the existing production workloads (VMs) that is running in the environment. However, you will lose access to:
Centralise management of VMs
vSphere functions, eg. DRS, vMotion, Fault Tolerance, High Availability, vSphere Distributed Switch, etc
In short, you will lose capabilities to manage VMs, configuration of new settings on vCenter and any HA/DR capabilities in the environment
"What do you think?"
Let me know if you think there is any important/useful details I have missed in the above write up.