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UUID stands for universally unique identifier (UUID). It’s a 128-bit value. vSphere uses it as IDs for many different types of entities like HostSystem, VirtualMachine, Datastore, etc.

The UUID surfaces to the vSphere API as well. You can find many methods use UUID as parameter or return result. The most commonly used one is the SearchIndex.findByUuid() which find you a virtual machine or a host based on its UUID, either instance or BIOS UUID. The format used for UUID is as follows:

52dc2e26-dbc4-7d05-5fed-019d234379d9

Since 4.0, DistributedVirtualSwitchManager managed object is added and it has a method called queryDvsByUuid(). As reported by VI Java API community, the standard format doesn’t work. The accepted format is like this:  Read more... (379 words, estimated 1:31 mins reading time)

What does a promotion mean for a virtual machine’s disks? When you get a promotion, you may have more salary, a better title, bigger office space, etc. For sure a virtual disk cannot earn salary and doesn’t care about title, but it can occupy bigger space in datastore.

In my previous blog, I discussed how to create linked virtual machines using vSphere API. These linked virtual machines share a common disk as base, therefore the total disk consumption is significantly reduced. When a virtual disk is promoted, it gets its own “office” other than sharing it with others.

The vSphere API to promote virtual disks is promoteDisks_Task defined with VirtualMachine type. It has a tricky parameter called “unlink” (type: boolean) . According to the API reference:

1. If the unlink parameter is true, any disk backing which is shared shared by multiple virtual machines is copied so that this virtual machine has its own unshared version. Copied files always end up in the virtual machine’s home directory.

2. Any disk backing which is not shared between multiple virtual machines and is not associated with a snapshot is consolidated with its child backing.

Now when should you use true or false? “If the unlink parameter is true, the net effect of this operation is improved read performance, at the cost of disk space. If the unlink parameter is false the net effect is improved read performance at the cost of inhibiting future sharing.”

Here is the sample code that illustrates the usage of the API:  Read more... (496 words, estimated 1:59 mins reading time)

Application Provisioning

With the right system configuration in place, it’s time to install the applications. So why not use the same tools we used for the OS and middleware? Do we need yet another set of tools?”

It depends. You can use the same set of tools for middleware to install some applications. The middleware appears like an application to the OS as well. The difference is whether your application is stable enough and whether you need to customize per node. The tools like Puppet can be good for stable applications that can be deployed the same way across all nodes. If your application is still a work in progress and you need flexibility to tweak it, you need more specialized application provisioning tools.

The big technical difference between application and middleware provisioning tools is that application tools push the application to the nodes and remotely change anything as needed. The process is procedural.

The middleware provisioning tools normally have agents on the nodes to pull the software based on the prescribed configuration files. The process is declarative.

Beyond the “push” and “pull” difference, the application provisioning tools can also manage the lifecycles of applications (sometimes called services) distributed on different nodes with a single line of command or code. Given the nature of remote command dispatching framework, the application provisioning tool can do almost anything. If there has to be a limitation, it’s your imagination.

So if you develop applications by yourself, you most likely need application provisioning tools.

Let’s see what tools are there.  Read more... (1601 words, 1 image, estimated 6:24 mins reading time)

Cloud computing is an evolutionary technology because it doesn’t change the computing stack at all. It simply distributes the stacks between the service providers and the users. In some sense, it is not as impactful as virtualization technology which introduced a new hypervisor layer in the computing stack and fundamentally changed people’s perception about computing with virtual machines.

But if you look closely at the latest IaaS clouds, they do leverage virtualization as a way to effectively and efficiently deploy systems. Inside one virtual machine, the computing stacks remain the same as before: from OS to middleware to application.

Keep in mind that the application is the end while the OS and middleware are the means. Customers care about applications more than the underlying infrastructure. As long as the infrastructure can support the applications, whatever the infrastructure might be is fine technically. Then the question would shift to the economic side: whatever is the most cost effective wins in infrastructure. That’s why Linux gains more shares in the cloud than in traditional IT shops.

To get to the end, you have to take a mean. In the IaaS cloud, you have to install the underlying OS and middleware before you can run your application. For the PaaS cloud, you can get away from that by focusing on application provisioning.

OS Provisioning

Remember, the software stack inside a virtual machine doesn’t change. It needs OS, middleware and application installed and configured before the application can work.  Read more... (1238 words, estimated 4:57 mins reading time)

With the growth of virtualization, a new term “virtual appliance” has been coined for a special type of virtual machines that are used like applications. What does it really mean?

First, a virtual appliance is still a virtual machine. When seen in vSphere Client, the virtual appliance does not look much different from other typical virtual machines. Secondly, the functionality of the virtual machine is limited to that of an application. More often than not, the virtual machine is installed with one application. Because of this, the underlying OS is stripped down only to the minimum required to support that application. This type of OS is also called Just Enough OS (JEOS). All the existence of the JEOS is to support the application in the virtual appliance.

Now, is it a VM or an application? It could be either, depending how you look at it. For ESX/vCenter, a virtual appliance is a virtual machine. You can manage it just like any other virtual machine. For application users, it’s an application, a special one that is different from a normal application.  Read more... (500 words, estimated 2:00 mins reading time)

Having answered many questions about IP addresses of virtual machines at different occasions, I still see more are coming. I think it’s time to write a blog about it. Hopefully people would search the Internet before raising the question.

First of all, there is a big confusion on the relationship of IP addresses and virtual machines. Many people tend to associate IP addresses with virtual machines, and want to retrieve/change the IP address of a virtual machine.

In fact, a virtual machine is very much like its physical counterpart. It does not have an IP address by itself. In other words, an IP address is NOT an intrinsic attribute of a machine, either virtual or physical. It might have one or more only after an OS is installed. In most cases, it does have one or more IP addresses, which gives the impression that every machine has an IP address.

A virtual machine does have intrinsic attributes such as MAC addresses if NIC cards are configured. Unlike its physical counterpart, a virtual machine’s MAC address can be re-configured. Some software vendors rely on MAC addresses to lock down their licensed software on particular machines. This mechanism can be, therefore, compromised in virtual environments.  Read more... (543 words, estimated 2:10 mins reading time)