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Does ESXi Support DDNS (Dynamic DNS)?

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An interesting feature request that was raised internally was for ESXi to support DDNS (Dynamic DNS) which allows a host client to update it's DNS record when using a DHCP Server. In most environments, to assign a hostname from DHCP, a DHCP reservation is used and this is maintained by the DHCP Server versus DDNS, where it is maintained by the client. Thanks to my colleague Eric Wager who did some quick research and found that ESXi does in fact supports DDNS and has been since ESXi 5.0.

I have not worked with DDNS much in the past and I have only seen it used for free/paid online services targeted at consumers to provide a well known address when their public IP Address changes frequently as with most ISPs. If your DHCP Server supports DDNS, this can be a handy feature to have, especially as you add new hosts you no longer have to manually create individual DNS record before hand and great for a lab environment. I did a big more digging to have a better understanding of how DDNS works with ESXi.

To enable support for DDNS on your ESXi host, you just need to set the hostname for the following ESXi Advanced Setting:

/Misc/PreferredHostName

You can do this in a variety of ways using either the vSphere Web/C# Client or using the command-line with ESXCLI.

Here is the syntax for the command:

esxcli system settings advanced set -o /Misc/PreferredHostName -s vesxi04.primp-industries.com

Once you have configured the setting, for the changes to go into effect, you will need to restart the management network. The easiest way to do this is via DCUI which you can run remotely by just typing dcui if you have an SSH session to your ESXi host. If you are using scripted install such as Kickstart, this can easily be automated as part of the post-install and upon first boot, DDNS will be enabled and configured with the proper hostname.

To test this in my lab environment, before enabling DDNS, I performed a reverse lookup of the assigned IP Address of my ESXi host from my DHCP server. In this example, the host received the address 192.168.1.135.

As you can see from the screenshot, a hostname could not be resolved as I would expect. After our changes, if we perform the reverse lookup again, we should now see the hostname that we had configured.

Another useful tidbit is the DHCP Client on ESXi is an ISC BIND implementation and this means if you require advanced things such as authentication keys, you can configured these options in /etc/dhclient-vmkX.conf where X is the specific VMkernel interface. For most deployments, you should not have to edit this file. Also if you want to prevent your DHCP Server from overriding the hostname of your ESXi host, you can add the following entry to the dhclient-vmkX.conf configuration file:

interface vmk0 {
   supersede host-name "vesxi04.primp-industries.com";
}

Just when I thought I knew about all the awesome features ESXi offers, it is a nice surprise to learn about another one!

Quick Tip - How to Change ESXi SSH Prompt

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This quick tip was motivated by a comment from Jason Nash where he wished the hostname of an ESXi host is automatically displayed on the SSH prompt when logging into the system. Traditionally, systems providing SSH access will default the SSH prompt to use the format of [username@hostname current-working-directory], but for an ESXi host, it just displays the current working directory.

This is not that big of an issue, unless you have multiple connections opened up to various systems which is usually the case for the average System Administrator. Being able to quickly identify the host you on are without having to run the hostname command would be nice and I can see why Jason would want to have this. Having said that, this is something you can easily configure on ESXi as well as other UNIX/Linux system in terms of customizing the SSH prompt.

To change the SSH prompt on ESXi, you will need to edit /etc/profile.local configuration file and add PS1 environmental variable which controls the SSH prompt. The configuration file is automatically backed up and all changes will persist through a reboot.

If you want to enable the basic [username@hostname current-working-directory], add the following to the file:

PS1="[\u@\h:\w] "

Now when you login to your ESXi host, the SSH prompt will look like this:

You can even add colors to your SSH prompt, if you add the following to the file:

PS1="\e[0;41m[\u@\h \W]\$ \e[m"

It will look like this:

The above are just examples of the customization you can apply to the SSH prompt, for more options you can take a look at this reference or search for others online. You can also quickly test your changes by just setting the PS1 variable on the command-line and then logging in.

Since this is something that has annoyed me from time to time, I will be filing a Feature Request with engineering and hopefully we can have this as a default in the future. Thanks Jason for bringing this up!

How to run Nested RHEV Hypervisor on ESXi?

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I have written a number of articles about VMware Nested Virtualization and even today, I am still surprised at how easy it is to virtualize not only our own hypervisor but other vendor's hypervisors as well. This week I received an interesting question from my old Technical Marketing colleague Rawlinson Rivera who wanted to run a nested RHEV (Red Hat Enterprise Virtualization) Hypervisor on ESXi. This was not something I had done before nor had any interest in doing and I told Rawlinson that it should technically work as long as the guestOS is enabled with VHV.

Rawlinson's attempt at installing RHEV resulted in the VM hanging after boot up. After a bit of research, it turns out some additional tweaks are required to get RHEV running on ESXi. I would like to give a huge thanks to Jim Mattson, one of the VMware developers who help made Nested Virtualization possible, for his assistance.

Disclaimer: This is not officially supported by VMware. Please use at your own risk.

Here are the instructions on creating a virtual machine that can be used to install RHEV (make sure you follow these exact steps, the VM must be created with these settings or it will not work):

Step 1 - Download RHEV 6.3 or 6.4 from Red Hat's website

Step 2 - Create a new Virtual Machine (vHW9) and when you get to the OS selection, you will need to select the following:

Guest Family - Other
Guest Version - Other (64-bit)

Step 3 - When you get to the virtual hardware customization, make sure you select LSI Logic SAS for the SCSI controller and also enable VHV under the CPU option.

Step 4 - Finally, you will need to add the following two advanced virtual machine settings:
vcpu.hotadd = false
apic.xapic.enable = false

Step 5 - Mount the RHEV ISO and once the VM starts to boot up, when you are presented with install/upgrade options, hit the TAB key. This will allow you to change the boot parameters and you will need to move your cursor to the left and remove "quiet" from the command-line which is right after the install keyword and then hit enter.

Note: This is required due to a known issue from Red Hat.

Step 6 - If everything was successful, you should be prompted with RHEV installer:

Step 7 - Once the installer has completed and you reboot, you now have nested RHEV running on ESXi!

Now it is time to delete the VM 😉