Published: November 12, 2007   |   Updated: February 25, 2008

The SoftGrid sequencer is essentially an application monitoring and packaging tool. However, the sequencer by itself will only package programs to its native .sft file format. With the MSI Utility discussed in the Standalone Mode decision, an MSI installer package is created that can install the .sft file into the client’s cache.

Sequencer Considerations

The SoftGrid application sequencer is an application that packages applications into a virtualized environment.

The sequencer application requires a workstation that should be configured ideally identical to a client workstation found in the production environment in which the SoftGrid infrastructure will be deployed. Applications should be sequenced on the lowest common version OS in the environment. Environments with both Windows® XP and Windows Vista®, in many cases, will sequence applications on a Windows XP–based client. However some applications may require separate sequencing for each OS that will be running the virtualized application.

An important part of building the sequencer workstation is making sure that library dependencies are installed. For instance, if an application uses Microsoft .NET Framework, the appropriate version should be installed on the client.

There are several exceptions to the above requirements. Notably, the sequencer should not install any agents or antivirus software. This requirement stems from the way the sequencer scans for resource usage while applications are being sequenced. It is possible to create a sequenced package with DLLs or other configuration information from antivirus software. In the case of agents, it may be possible to capture information that is unique to a single instance of the agent.

Application dependencies occur when a software package requires a particular application to function properly. If the application cannot be installed on all workstations natively, it will need to be sequenced into the SoftGrid-enabled application. For example, many applications require a custom SQL Server 2005 Express instance. If the instance is not installed by the application, it may be necessary to sequence both the SQL Server Express and the application requiring SQL Server into the same package.

The sequencer workstation can be either a physical workstation or a virtual workstation.

Physical Sequencer

The following considerations should be taken into account when planning to use a physical sequencer:

• When using a physical workstation, a reference disk image of the computer needs to be created once the sequencer is installed. Each time an application is sequenced, the image should be reapplied to the workstation to reset the computer. Physical Machine Sequencing will be able to sequence an application much more quickly.
• With its slower reset time, the system will need to be re-imaged in order to sequence the next application.
• If the application has specific hardware library dependencies, such as graphics accelerators (for example, CAD software), a physical server might be more desirable.

Virtual Sequencer

Virtual machines are ideal for sequencing applications and can be quickly and easily reset using undo disks. They will also require two virtual hard disks, the second disk being dedicated to the virtual drive used by the SoftGrid client.

The following considerations should be taken into account when planning to use a virtual sequencer:

• There is a fast machine reset time. Using undo disks, it is possible to quickly revert a sequencer to its base environment. This is ideal for sequencing many applications.
• The system is slower to sequence applications due to running in a virtual machine. This does not usually cause a significant issue.

The Application Sequencer system environment must also be configured to match deployment environments. A SoftGrid package uses a virtual drive on the client to store sequenced application files. When building the sequencer, it is important to physically designate a drive on the computer used for sequencing. By default, this is a drive mapped to drive Q. On a physical computer, this can be a separate partition mapped to the sequencer drive letter, or it can be a new hard drive in the computer. In a virtual machine, this is best defined as a new virtual drive and is then configured as drive Q in Windows Volume Manager.

Task 1: Placing the Sequencer

Antivirus packages can create issues during sequencing as any changes done to the AV can be captured by the sequencing process. For example, a new signature update could be captured as part of the application sequencing. When this application is run, the signature could potentially interfere with the operation of the clients AV, particularly if there are more recent signature updates. Because of this, sequencers are frequently configured without AV. If the sequencer does not have an antivirus package installed, it is recommended that the sequencer be placed in an isolated environment that is disconnected from the production network. This reduces the risk of the sequencer being affected by malware.

In some cases, it may be necessary to allow the sequencer workstation to communicate with a production server to fully configure and test an application. In these scenarios, it may be necessary to run antivirus software on the sequencer to comply with corporate policy. If antivirus is installed, it is recommended that it is disabled during sequencing. Alternatively, the server infrastructure can be reproduced in the sequencer environment; however, this will increase the complexity of configuring and managing the sequencing environment.

Each sequenced application should also be tested in a pre-staging environment where the normal agents and base applications are already installed. This ensures that the sequenced application is not going to have any issues and will not cause any problems on a fully deployed workstation. This precaution can also be used to scan the sequenced applications for viruses.

Special Note for Standalone Mode

Although the MSI packager can also be placed on the sequencer, it is recommended to run the MSI utility on a separate machine. This is to reduce the risk of introducing a dependency that is not available on the organization workstations. The sequencer configuration should match the configuration of a production machine as closely as possible. The MSI packager could be a workstation or another server.

Task 2: Choosing a Sequencer Location

In situations with multiple SoftGrid instances, the question as to where to place a sequencer is often asked. In most cases, the sequencer environment should be deployed to the same location that manages applications for the organization. If the organization has a distributed administrative model, it could be necessary to have a sequencer environment wherever there is an administrative authority.

Validating with the Business

• Is there a central location where it makes more sense to package applications? As application management becomes more centralized, it might be more practical to re-assign the application responsibilities to a centralized team. This allows for a reduction in overall IT costs. SoftGrid also allows for a very consistent experience, even if the application was not sequenced on location.

Decision Summary

The SoftGrid sequencer needs to be placed in an isolated environment. The sequencer should also be set up so that its configuration is as similar to a reference client system as possible. Deciding whether to sequence on a virtual environment or a physical environment is an important consideration.