VMware vSphere is a suite of software components for virtualization. These include ESXi, vCenter Server, and other software components that fulfill several different functions in the vSphere environment.

vSphere includes the following software components:

The hypervisor runs virtual machines. Each virtual machine has a set of configuration and disk files that together perform all the functions of a physical machine.

Through ESXi, you run the virtual machines, install operating systems, run applications, and configure the virtual machines. Configuration includes identifying the virtual machine’s resources, such as storage devices.

The server provides bootstrapping, management, and other services that manage your virtual machines.

vCenter Server
A service that acts as a central administrator for VMware ESXi hosts that are connected on a network. vCenter Server directs actions on the virtual machines and the ESXi hosts.

vCenter Server is a single Windows or Linux Service and is installed to run automatically. The vCenter Server service runs continuously in the background. It performs its monitoring and managing activities even when no vSphere Clients are connected and when no one is logged on to the computer where it resides. It must have network access to all the hosts it manages.

You can install vCenter Server on a Windows virtual machine or physical server, or deploy the vCenter Server Appliance. The vCenter Server Appliance is a preconfigured Linux-based virtual machine optimized for running vCenter Server and the vCenter Server components. You can deploy the vCenter Server Appliance on ESXi hosts 5.5 or later, or on vCenter Server instances 5.5 or later.

All prerequisite services for running vCenter Server and the vCenter Server components are bundled in the VMware Platform Services Controller. You can deploy vCenter Server with an embedded or external Platform Services Controller, but you must always install or deploy the Platform Services Controller before installing or deploying vCenter Server. All vCenter Server services and some Platform Services Controller services run as child processes of the VMware Service Library Lifecycle Manager service. See the vCenter Server Installation and Setup documentation for details about setting up this configuration.

vCenter Single Sign-On
A service that is part of the vCenter Server management infrastructure. The vCenter Single Sign-On authentication service makes the VMware cloud infrastructure platform more secure by allowing the various vSphere software components to communicate with each other. The vCenter Single Sign-On authentication service uses a secure token exchange mechanism instead of requiring each component to authenticate a user separately with a directory service like Active Directory.

When you install vCenter Single Sign-On, the following components are deployed.

STS (Security Token Service)
STS certificates enable a user who has logged on through vCenter Single Sign-On to authenticate to any vCenter service that vCenter Single Sign-On supports. The STS service issues Security Assertion Markup Language (SAML) tokens. These security tokens represent the identity of a user in each of the vCenter Single Sign-On identity sources.
Administration server
The administration server allows users with vCenter Single Sign-On administrator privileges to configure the vCenter Single Sign-On service and manage users and groups from the vSphere Client. Initially, only the user [email protected] has these privileges.
vCenter Lookup Service
vCenter Lookup Service contains topology information about the vSphere infrastructure, enabling vSphere components to connect to each other securely. Unless you are using Simple Install, you are prompted for the Lookup Service URL when you install other vSphere components. For example, the Inventory Service and the vCenter Server installers ask for the Lookup Service URL and then contact the Lookup Service to find vCenter Single Sign-On. After installation, the Inventory Service and vCenter Server system are registered with the vCenter Lookup Service so other vSphere components, like the vSphere Client, can find them.
VMware Directory Service

Directory service associated with the vsphere.local domain. This service is a multi-tenanted, peer-replicating directory service that makes an LDAP directory available on port 389. The service still uses port 11711 for backward compatibility with vSphere 5.5 and earlier systems. In multisite mode, an update of VMware Directory Service content in one VMware Directory Service instance results in the automatic update of the VMware Directory Service instances associated with all other vCenter Single Sign-On nodes.

vCenter Server plug-ins
Applications that provide additional features and functionality to vCenter Server. Typically, plug-ins consist of a server component and a client component. After the plug-in server is installed, it is registered with vCenter Server and the plug-in client is available to the vSphere Client for download. After a plug-in is installed on the vSphere Client, it might alter the interface by adding views, tabs, toolbar buttons, or menu items related to the added functionality.

Plug-ins leverage core vCenter Server capabilities, such as authentication and permission management, but can have their own types of events, tasks, metadata, and privileges.

Some vCenter Server features are implemented as plug-ins, and can be managed using the vSphere Client Plug-in Manager. These features include vCenter Storage Monitoring, vCenter Hardware Status, and vCenter Service Status.

vCenter Server database
Persistent storage for maintaining the status of each virtual machine, host, and user managed in the vCenter Server environment. The vCenter Server database can be remote or local to the vCenter Server system.

The database is installed and configured during vCenter Server installation.

If you are accessing your ESXi host directly through the VMware Host Client, and not through a vCenter Server system and associated vSphere Client, you do not use a vCenter Server database.

Many vCenter Server functions are implemented as web services that require the tcServer. The tcServer is installed on the vCenter Server machine as part of the vCenter Server installation.

Features that require the tcServer to be running include: lCIM/Hardware Status tab, Performance charts, WebAccess, Storage Policy-Based services, and vCenter Service status.

vCenter Server agent
On each managed host, the software that collects, communicates, and runs the actions received from vCenter Server. The vCenter Server agent is installed the first time any host is added to the vCenter Server inventory.
Host agent
On each managed host, the software that collects, communicates, and runs the actions received through the vSphere Client. It is installed as part of the ESXi installation.