vCenter Server: Installable versus Appliance. Often when designing an infrastructure there is a choice to be made between the two options. Go for the easy and fast to deploy appliance or go for the scalable and flexible installation. Where with the previous version of ESX before version 5.5 the vCenter Server appliance was limited, when using the embedded database, to environments of up to 5 ESXi hosts and 50 virtual machines. Now that the maximum is raised to 100 supported ESXi hosts and 3000 supported VMs you have a new viable choice to go for the appliance with the internal database. New in vSphere 5.5 is support for clustering of the vCenter Server Database, this can be a  viable option because the vCenter server heavily depends on the database that is used to store configuration and statisticals.

The following is a comparison between the Appliance and the Installable version of vCenter Server:

vCenter ServerApplianceInstallable
Running onA pre-configured SUSE Enterprise Linux based virtual applianceThe installable version is a Windows application supported on Windows Server 2008R2 64-bit and Windows Server 2012.*Service pack information should be verified before installation in either a virtual or physical machine
PackageOVF templateISO file
Server Virtual or PhysicalVirtualVirtual or Physical
Database
Database internalvPostgreSQL databaseMicrosoft SQL Express database
Supports #ESXi host1005
Supports #VM’s300050
Larger environment?Use an external databaseUse an external database
External Database supportedOracleMicrosoft SQL or Oracle
vCenter Server Options
Auto DeployPre-installedSeparate installation
Syslog CollectorPre-installedSeparate installation
ESXi Dump CollectorPre-installedSeparate installation
vSphere Web ClientPre-installedAs part of vCenter Install
Single Sign-OnPre-installedAs part of vCenter Install
Scripting & Automation of the DC
vSphere CLICannot be installedSeparate installation
PowerCLICannot be installedSeparate installation
Network
IPv4 or IPv6 supportSupports IPv4 OnlySupports IPv4 and IPv6
vCenter Update ManagerCannot be installed insideCan be installed on the vCenter Server
Linked ModeNot compatibleCompatible
vCenter HeartbeatNot compatibleCompatible

Note: the Syslog Collector and ESXi Dump collector must be registered as a plug-in in vCenter Server.

vCenter Server

vCenter Server is comprised of a number of interlinked components and interfaces to other services and infrastructure. I will describe each of the key components and their role in vCenter below.

  1. vCenter Single Sign-On
  2. vCenter Inventory Service
  3. vCenter Server (Core)
  4. Web Client

1. vCenter Single Sign-On

Offers administrators a deeper level of authentication services that enable VMware solutions to trust each other. SSO allows VMware solutions to utilize multiple directory services and is no longer limited to Microsoft Active Directory. It simplifies the management of multi-site and multi-installation environments by allowing users to move seamlessly between multiple environments without re-authentication. A SSO server can be installed separately and can support multiple vCenter installations. The SSO server must be able to communicate with your identity sources such as Open LDAP, Microsoft Active Directory or a Local Operating System.

2. vCenter Inventory Service

Optimizes client server communications by reducing the number of client requests on vCenter Server. It is now a separate independent component that can be off-loaded to a separate server. (Installable version only!) This can be used to reduce traffic and improve client response times. It also enables users to create and add inventory object-level tags.

These are then used to organize and provide quicker retrieval when performing inventory searches. The inventory service must be able to communicate with the SSO server, the vCenter Server and the client.

3. vCenter Core

Core Services

Are the basic management services for a virtual Data Center. These include virtual machine provisioning; statistics and logging; host host and virtual machine configuration; alarms and event management; and task scheduling. The vCenter Server must be able to communicate with the ESXi hosts and must be accessible to any systems that require access to the API.

Distributed services

Are solutions that extend VMware vSphere capabilities beyond the single physical server. These solutions are DRS, HA, vMotion. They are configured and managed centrally from vCenter Server.

vCenter API

Provides access to the vSphere management components. These are the objects that you can use to manage, monitor and control lifecycle operations of virtual machines and other parts of the virtual infrastructure. (Networks, Datastores, Datacenter, etc.)

The vCenter API provides the interface to vCenter that is used by the vCenter Clients, third party applications, plug-ins and VMware applications such as vCAC. It is available for administrators, developers and partners to integrate and automate solutions.

4. Web Client

Provides a rich application experience in a wide variety of web browsers. This surpasses the functionality of the trusted VMware vSphere Client (the VI or Desktop Client) running on Windows.

Can be installed on the vCenter Server along with other vCenter Server components or it can be installed on a Windows Management server or Windows desktop. The Web Client is accessed via a Web browser that connects to the Web Client Server. The web clients is now the primary management client, because from vSphere 5.5 all of the new vSphere features are only available when using the Web Client interface. (New vSphere 5.5 features include: 62TB VMDK, vFlash Configuration)

Features only available with:

vSphere Desktop ClientvSphere Web Client
VMware Desktop Plug-ins (SRM, etc)vCenter Single Sign-on: Authentication, Administration
3rd Party Desktop Plugins (various)Navigation with inventory lists
VXLAN NetworkingInventory Tagging
Ability to change Guest OS on an exisiting virtual machineEnhanced read performance utilizing the Inventory Service
vCenter Server MapsvSphere Replication
Create and edit custom attributesVirtual Infrastructure Navigator
Connect directly to a vSphere hostEnhanced vMotion (no shared storage)
Inflate thin disk option found in the Datastore BrowserIntegration with vCenter Orchestrator (cVO) Workflows (Extended Menus)
Virtual Distributed Switch (vDS): Health Check, Export/Restore Configuration, Diagram Filtering
Log Browser Plugin
vSphere Data Protection (VDP)

Note: All of the mentioned services rely heavily on DNS.

Additional resources:

VMware Product Interoperability Matrixes

vCenter Server Maximums, see page 7

vCenter Database Size Calculator

Installing vCenter Server 5.5 best practices (2052334)