The third drop-down section of the main tree manages the Virtual Desktop Infrastructure (VDI) of flexVDI. It is configured through two kind of objects: Terminal and Desktop Policies. Terminal Policies apply to the terminal the user is connecting with, and desktop policies apply to the desktops a user is allowed to access. In order to fully understand these concepts, let's see how the flexVDI Manager decides which desktop is shown when a user connects to the platform:
In this section, we will explain in detail how Terminal and Desktop Policies are configured, and the best practices to manage them in a useful way.
A Terminal Policy groups together a set of terminals (flexVDI Client software). When a terminal identifies itself with its TID, the Manager selects a Terminal Policy for it:
The Manager then uses the Terminal Policy to get the list of Desktop Policies that will be presented to the user. In an unauthenticated policy, this list is directly stored in the policy. In an authenticated one, the list is retrieved from an LDAP server.
A terminal can be moved from one Terminal Policy to another, or even unregistered. In this way, you can create Terminal Policies for specific groups of terminals, and have a "default" policy for other terminals and the new ones. For instance, there can be a group of public kiosk terminals that require no authentication to connect to a desktop, and the rest of terminals, which must be authenticated.
In the end, the result of applying a Terminal Policy is a list of Desktop Policies, from which the user will pick one. The syntax of this list, in the policy or the LDAP directory, is a comma-separated sequence of items. Each item may be:
Each item may be followed by the text that will be presented to the user in the selection box. For instance, an item can be "w7prox64" or "w7prox64=Windows 7 Professional 64-bit". In the first case, the user will see the text "w7prox64", while in the second case the user will see the much more informative text "Windows 7 Professional 64-bit".
Authenticated policies contain all the parameters needed to query an LDAP server:
When the Terminal Policy is authenticated, the client asks the user for a username and a password, and passes them to the Manager. The Manager then authenticates the user against the LDAP server and retrieves the list of Desktop Policies. This list is created by merging the values of the desktop attribute from the following LDAP entries:
If neither the user or any of the groups it is member of contain a list of Desktop Policies, the default list is returned.
You can see how to configure an authenticated policy in the First steps guide.
In many scenarios, you will want to have different authentication domains; e.g. different LDAP branches for each department in a big company, or even different LDAP servers for each client in a multi-tenancy platform. You need to create a different policy for each domain. However, manually registering terminals to each policy can be an cumbersome task. Named Terminal Policies solve this problem by associating a Terminal Policy with the host name the clients are using to connect with the Manager:
Usually, you will want your "default" Terminal Policy to be authenticated and/or use named policies. In this way, your users will be able to move to new, unregistered terminals (like their phone or tablet, or a new computer) and still be able to access the platform without you having to register the new terminals explicitly. Then, you can create additional unauthenticated policies for public kiosk-type terminals. Other common groups of terminals are classrooms, laboratories, office floors, etc.
Use a desktop attribute that already exists in your LDAP directory schema, but is not in use, so that you do not need to modify the schema. If you are using an Active Directory, a suitable attribute would be "info" (or Comment in the AD nomenclature). It can be easily edited with the "AD Users and Computers" tool, where it appears as a big text box labeled "Notes", for both users and groups.
A Desktop Policy contains many information that controls how a desktop is instantiated for a user. Most of it was explained when we configured an unauthenticated Terminal Policy in the First steps guide. Here we will go again through the new Desktop Policy wizard explaining the meaning of all the fields. The first page asks for the following information:
Next, you must select the pool from which resources will be taken. New desktops will consume resources (vCPUs and RAM) from this pool. If not enough resources are present in the pool for new desktops, the VDI session will fail and an error will be returned to the client:
The next page allows you to select the template that will be used to create users' dekstops. Every time a new desktop is needed, a clone of this template will be created:
Then, you will have to decide where you want to store the images of the cloned desktops. As explained before, these images only store the differences with the template's ones. For historic reasons, these images where stored in
/var/lib/flexvd/volatile, in the host where the cloned desktop is started. In this page you can decide whether to keep using that path or select a different volume. It is a best practice to mount fast (SSD) local storage in that path:
Finally, you can decide what capabilities will be available for the desktops of this Desktop Policy, and what happens when a user finishes a VDI session:
Session capabilities can be restricted to prevent information leaks, use of restricted resources, etc... The available capabilities are:
The USB redirection, power actions and the multi-client feature are applied when a new desktop is created, and they will not change during that desktop's lifetime. The other capabilities are applied when a user connects to a desktop and will not change during the session's lifetime. Take that into consideration when you modify the capabilities of a Desktop Policy that currently has running desktops and/or active user sessions.
Besides, the flexVDI Client accepts command line arguments that enable or disable some of these capabilities. In each case, the most restrictive setting applies (like disabling the clipboard or a shorter inactivity timeout).
This page also lets you specify up to three actions that will take place once the user has disconnected from its desktop and the session ends. For each operation you must specify an amount of time and an action. Then, the action will be performed on the desktop that amount of time after the session ends. If the user connects again before the time of an operation elapses, the action is not executed. The possible actions are:
Pause, suspend, stop and shutdown will leave the desktop in a state that is recoverable. Furthermore, the guest will be started again when its user connects. On the other hand, if a desktop is destroyed it will be shut down and its state removed. When the user connects again, a new desktop will be created for him or her.
These operations are best suited to automatically recycle volatile desktops. For instance, if your users connect everyday from Monday to Friday and you want to recycle the desktops on weekends, you can destroy desktops after 1 day. Or you may destroy desktops after just some hours of being idle. Pausing desktops when the users disconnect is also a good way of not wasting CPU resources, because resuming from paused state is almost instantaneous. Using volatile desktops, with precreated instances and automatic recycling provides a great VDI experience.
One of the most common tasks of a flexVDI administrator is to update the template assigned to a Desktop Policy. This can consist in updating the software, installing new programs, applying some patches, etc... In general, any action that modifies a template's disk images. The problem is that a template cannot be directly modified. It must be first converted into a standalone guest, and in order to do so it must have no cloned guests. As a result, a pre-condition to modify the template of a Desktop Policy is to destroy all the desktops cloned from that template. This also means that your desktops must be volatile. More on how to configure your guests so that they are volatile in this page of this guide.
However, in order to avoid destroying the desktops of users that are currently using them while you modify the template, the preferred way of updating a Desktop Policy's template is the following:
From now on, when new desktops are created under this Desktop Policy, they will make use of the new template. The desktops that were already running with the old template will not be affected. Then, you can configure your Desktop Policy so that the desktops are destroyed when the users disconnect, so that the next time they connect an updated desktop will be created for them. Once all the desktops cloned from the original template are destroyed, it can be deleted if desired.