Question

What’s the reason to create a VM snapshot before starting the lab?

When would it be smart to make a snapshot before any major changes to a VM? When could a snapshot be a problem?

Why do we use the “AD” subdomain for the domain and not just use the 2^nd level domain <ASUrite ID>.lan?

Why is using a top-level domain of “lan” a bad idea?

What is meant by “split brain” DNS?

Answer 1

1) The state of a virtual machine at any specific point in time can be preserved by taking what is known as a snapshot.

The VMware snapshot feature is particularly useful in those scenarios where you want to quickly recover from a failure or simply revert back to a desired state. Restoring a VM to a functional state following a botched update or patch is one common use-case. Similarly, you can use snapshots to reset a VM back to a baseline state once a user is done using it, perhaps as part of a training lab maintenance regimen.

The snapshot feature is available on both standalone ESXi hosts and vCenter Server.

You can work with snapshots from any vSphere client or by making API calls from PowerCLI or similar. Different tasks such as reverting from snapshot, deleting snapshots, etc. follow the same click and select pattern. The common denominator here is Snapshot Manager using which, you’ll be able to:

Take snapshots.
Revert to the latest snapshot or any other snapshot.
Delete a snapshot.
Delete all snapshots.
Edit a snapshot (Name and Description).
Manage snapshots.
Consolidate disks.

Each snapshot creates an additional delta file. When you take a snapshot, the snapshot mechanism prevents the guest operating system from writing to the base .vmdk file and instead directs all writes to the delta disk file. The delta disk represents the difference between the current state of the virtual disk and the state that existed at the time that you took the previous snapshot. If more than one snapshot exists, delta disks can represent the difference between each snapshot. Delta disk files can expand quickly and become as large as the entire virtual disk if the guest operating system writes to every block of the virtual disk.

2)You can restore a snapshot in VMware Workstation by using the Revert and Go to commands. The following sections explain how these commands work.

The Parent Snapshot
The parent snapshot of a virtual machine is the snapshot on which the current state (the You Are Here position) is based. After you take a snapshot, that stored state — the parent snapshot of the current state — is the parent snapshot of the virtual machine. If you revert or go to an earlier snapshot, the earlier snapshot becomes the parent snapshot of the virtual machine.

Revert to Snapshot
Revert is essentially a shortcut for Go to the parent snapshot of the virtual machine — that is, the parent snapshot of the You Are Here position. Revert immediately activates the parent snapshot of the current state of the virtual machine. The current disk and memory states are discarded, and the virtual machine reverts to the disk and memory states of the parent snapshot.

To Revert to the parent snapshot, choose VM > Snapshot > Revert to Snapshot, or click the revert button on the toolbar.

Go to Snapshot
This command activates the snapshot currently selected in the snapshot manager. Unlike Revert, the Go To command is not limited to the parent snapshot of the current state. You can choose any snapshot.

To go to a snapshot, choose VM > Snapshot and select the snapshot by name; or, in the snapshot manager, select a snapshot and click Go To.

Reverting at Power Off
This setting causes the virtual machine to revert automatically to the parent snapshot any time it is powered off. The parent snapshot of a virtual machine is the snapshot on which the current state (the You Are Here position) is based (see The Parent Snapshot).

There are a number of limitations you need to be aware of. A few, such as those related to how snapshots interact with vMotion, need to be properly addressed if you’re still using older versions of vSphere.

Snapshots of VMs with raw disks, RDM physical mode disks, or guest operating systems using an iSCSI initiator in the guest are not supported.

• VMs with independent disks must be powered off before you take a snapshot.
• Snapshots of powered-on or suspended VMs with independent disks are not supported.
• Snapshots are not supported with PCI vSphere Direct Path I/O devices.
• Snapshots of VMs configured for bus sharing is not a VMware supported option.
• Although snapshots provide a point-in-time image of the disk that backup solutions can use, these are not meant to be a robust method of backup and recovery. If the files containing a virtual machine are lost, its snapshot files are also lost. Also, large numbers of snapshots are difficult to manage, consume large amounts of disk space, and are not protected in the case of hardware failure.
• Snapshots can negatively affect the performance of a virtual machine. Performance degradation is based on how long the snapshot or snapshot tree is in place, the depth of the tree, and how much the virtual machine and its guest operating system have changed from the time you took the snapshot. Also, you might see a delay in the amount of time it takes the virtual machine to power-on. Do not run production virtual machines from snapshots on a permanent basis.
• if a virtual machine has virtual hard disks larger than 2 TBs, snapshot operations can take significantly longer to finish.

If you have pre-vSphere 6.0 environments, make sure to read the Migrating virtual machines with snapshots KB article. A common issue I used to come across frequently, was one where you’d put a host in maintenance mode and wait for the VMs to migrate off of it automatically, only to find the process stuck because one or more VMs had snapshots

Split-Brain DNS

Split-Brain DNS, Split-Horizon DNS, or Split DNS are terms used to describe when two zones for the same domain are created, one to be used by the internal network, the other used by the external network (usually the Internet). I prefer the term "Split DNS" so we will just continue with that one.

A Split DNS infrastructure is used to direct internal hosts to an internal domain name server for name resolution and external hosts to an external domain name server for name resolution. This type of DNS configuration is very common in networks that have established an internal Active Directory domain name which is the same as the public external domain name. Let's begin by taking a look at an example where Split DNS is not used.

issues and concerns that may need to be addressed by implementing a Split DNS design.

• The internal DNS zone is exposed to Internet users. An Internet user can resolve ALL internal host names.
• One or more internal servers are exposed to the Internet. This can lead to exposing data due to security vulnerabilities in other services running on the servers.
• If the organization has an Internet and intranet web site, name resolution for the web site using one host name is extremely complex without additional components. For instance, the URL, would point to the same resource even though there would be an intranet and Internet web site established.