In this post, I am providing steps in brief to restart the Management Agents on ESXi Hosts using 2 methods : Either by connecting to the Host via a Secure SSH Putty Session OR by taking a remote session of the ESXi Host.

Please note that by restarting the Management Agents, there is no impact to running VMs on this Host, It restart the Management Services which help in communicating with VCenter this Host is connected to.

A) By SSH Putty Session
Run the following commands to restart the Management Agents

/etc/init.d/hostd restart

/etc/init.d/vpxa restart

To check the status of these agents, run the following commands

/etc/init.d/hostd status

/etc/init.d/vpxa status

B)  From Remote Console

1. Connect to the console and Press F2 to Login
2. Enter Root Username and Password
3. Navigate to Troubleshooting Mode Options -> Restart Management Agent and Press Enter
4. Press F11 to confirm the Management Agent Status

There are multiple ways to find the serial number of the ESXi Host. Check the Serial Number physically inscribed on the server. It may or may not be present in the Configuration Tab of the ESXi Host when checked from vCenter Console.

It may not be always available in the configuration tab and in order to find the serial number of a Host, we can fetch the details like Make\Model and Serial No from SSH.

1. Open Putty and connect to the ESXi SSH console using root account credentials
2. Run the following command to get the serial no
                            esxcli hardware platform get
3. We get the required details as shown below

The best thing about Vmware platform is the centralized management of all the resources using vCenter Server. Using vSphere or Web Client we all connect to vCenter Server to administer the virtual datacenter. Imagine if there was no vCenter Server and we had to connect to each ESXi host manually and manage the VMs. Yes, it sounds like a tedious task.

vCenter Server also provides multiple features like DRS, sRDS, vMotion, HA, FT etc. Today we are talking about a scenario where the vCenter Server or Appliance goes down and what are its impact on each of these functionalitiess. Let's check the impact of each of these functionalities below

Management :

Managing the environment won't have much impact as we can still connect to each ESXi host via SSH or vSphere client and manage the servers. It is not easy but there is no impact to the environment

Virtual Machines & ESXi Hosts:

There is no dependency of vCenter server on functionality or uptime of any other Virtual Server or ESXi Host. The Hosts can still be connected via SSH or vSphere Client and all the Virtual machines are still working

Distributed Resource Scheduling:

DRS works with vCenter Server to balance the resources and Virtual Machines across ESXi Hosts using DRS Clusters, the DRS functionality will fail if the vCenter server is down

vMotion\svMotion:

vMotion and svMotion features are spanned across hosts and since it is a feature is based on DRS, Both vMotion and svMotion will fail if vCenter server is down

High Availability:

HA will have medium impact as the Hosts\Clusters configured with HA enabled will have the HA running even if vCenter Server is down. However we would not be able to change any settings like Admission Control Policies while the vCenter Server is down.

Fault Tolerance:

FT will also work in case of all Virtual Machines which are configured before vCenter Server went down. No Changes can be done once the vCenter server is down.

Distributed Switch:

Distributed Switch would still continue to work even after vCenter Service is down. It will still connect to the Network it is configured on.

VM Snapshots:

There would be no issues in taking the snapshots of a Virtual Machine. We need to connect to ESXi host and take the VM snapshot.

Virtual Update Manager:

Since Virtual Update Manager is a vCenter plugin, the functionality of VUM will fail while the vCenter is down.

Note:

We have tested these features and impacts mentioned above only on vCenter Server 5.x version only. 

Below is a checklist that can be followed for ESXi Build. There could be some points which I might have missed, please let me know in comments if I can add anything extra

SL	Checks
1	Racking and Stacking for Cisco UCS Server
2	CIMC configuration (IP, CIMC Name, DNS & Standard CIMC Password)
3	DNS Records creations for CIMC & ESXi Servers
4	Verification of CIMC connectivity with CIMC Hostname
5	ESXi Installed on Local Storage or SAN
6	ESXi Version
7	Addition of ESXi in the required vCenter
8	NTP Configuration
9	DNS & Routing Configuration
10	License Configuration for ESXi
11	Boot LUN rename (esxiname_boot_lun)
12	Add ESXi Servers in Distribution Switch
13	DvSwitch Creation [if not created already]
14	Management PortGroup Creation
15	Create vMotion & Virtual Machine Traffic PortGroup in DvSwitch
16	Configure Port Channel with LACP on switch ports
17	Configure Teaming and Failover Policy as – Route Based on IP Hash [if above step is done]
18	Create NFS PortGroup and VMKernel IP Configuration
19	Existing Datastore allocation to New ESXI Server
20	Configure Scratch Partition on Shared Storage
21	Addition ESXi Host in HA DRS Cluster
22	Creation and Configuration HA DRS cluster [if not already]
23	DRS Set to Fully Automatic
24	Configure EVC [Enhance vMotion Compatibility] for ESXi Cluster
25	Fix Errors / Warnings for ESXi Host [if any]
26	Verification of vMotion Functionality
27	Add ESXi Server in Monitoring
28	Add ESXi Server in Cisco CIMC Supervisor [if it is a Cisco Server]
29	Addition of Cluster and Datacenter in CMDB together with ESXi