This document outlines the basic operating principles of Glazier.
From a high level, imaging any system requires the following:
Glazier is no different. Glazier’s Autobuild library provides a means of dynamically selecting the image(s), application(s), and configuration(s) to be applied to a host. It retrieves any required files over the network, executes scripts and binaries, and modifies the host as required.
Glazier is heavily network-based. Rather than attempt to provide complete, pre-configured operating system images, which are laborious to maintain, Glazier emphasizes maintaining basic images, and distributing all required customization via the network.
Glazier has no graphical interface. Glazier focuses on keeping all data about the imaging process exposed to the administrator, where it is most accessible and most powerful.
A Glazier environment will consist of a minimum of:
Regardless of the platform, imaging requires a working host environment capable of running the installation tools. Glazier can theoretically run from any type of boot environment, but it was designed to work with WinPE.
WinPE gives us all the capabilities needed to discover information about the local host (as Windows will see it), retrieve our installation files, and bootstrap the install process. Customizing a PE environment is fairly simple and familiar to most Windows administrators. PE images can be distributed via the network (PXE boot), via file (ISO), or portable storage (USB, etc).
Because Glazier is Python-based, the PE or other boot media must contain a Python interpreter. You can place the Glazier code and dependencies directly in the PE, or for more advanced users, you can write a custom launcher to accomplish this.
WinPE should be configured to automatically launch the installer tool. For Glazier, this is usually Autobuild.
Producing a new PE image can be an error-prone and time-consuming process. Glazier is a network-based system and follows the general model that most files needed for installation can be retrieved at install time. The theory is that it is much easier to change network-based files in a controlled, predictable, and low-overhead way than it is to regenerate a WIM or PE image containing the same changes. In other words, we always attempt to minimize the need to generate new boot images by pushing most routine changes into Glazier’s dynamic environment.
For advanced users, we recommend creating a simple launcher which will run directly from winpeshl.exe that leverages the configuration file (winpeshl.ini) to retrieve the initial files required from a web server. This prevents the need to generate a new PE if any changes are required to Python, Glazier, or any other bundled dependencies.
Autobuild is the central component of the Glazier system. It contains the logic for host discovery, file retrieval, configuration handling, and for implementing several basic installation actions.
When first run, Autobuild should be directed, via a command-line flag, to the web server hosting the installation configuration files. It will retrieve the root configuration file and begin parsing it. Glazier will compare the commands it finds in these files to what it discovers about the state of the host (hardware, network, etc). It may also be configured to prompt the user for input.
Based on the configuration files and the host state, Autobuild prepares a chronological list of actions. This list of actions instructs every operation performed via Glazier to producing a fully provisioned device.
Once autobuild has reached the end of the available configuration files, it will have produced a list of pending actions for the localhost. It will then begin executing them in order. It will end when the last action is completed, or any of the required actions fail.
Autobuild’s ability to handle configuration is entirely freeform. It could easily be used for tasks other than imaging. In the case of imaging, a successful configuration will tend to follow a common series of events, but these are entirely up to the administrator:
It will take time to build a complete end-to-end configuration for the first time. However, subsequent changes are often trivial, and it becomes very simple to branch into different configurations once you have a working foundation, as explained below.
The Glazier Build YAML Specification page goes into detail about the format of Glazier’s configuration files.
“Text files” may seem like a surprising foundation for an imaging system, however, they are ultimately one of the most powerful and flexible options available. GUI-based systems limit the administrator to only the features and capabilities built into the GUI by the manufacturer. The “data” held behind the GUI is often obscured and inaccessible.
With Glazier, the configuration files hold your imaging data in raw and unrestricted form. Autobuild will parse them, but how you choose to manage them may grant numerous additional benefits.
You can modify Glazier configs in the text editor of your choice, meaning thousands of options are available, for free, on any platform. Because YAML is an open standard, any text editor with YAML support will give additional benefits, such as automatic syntax highlighting.
Like computer code, Glazier’s text files are a perfect fit for a version control system (VCS). It is highly recommended to maintain your Glazier configuration tree (and any associated scripts) inside a VCS. This produces many immediate benefits to the administrator, including:
A simple Glazier deployment will involve a single configuration root, which may be all that is required for small environments. Larger or more sensitive environments will want to employ QA procedures. This is trivial with Glazier’s text-based format, and particularly so when combined with a version control system.
Create multiple “root” directories, such as unstable, testing, and stable. Make initial changes in the unstable root, and deploy them to testing and stable. Once vetted, the configuration files can be copied or integrated over to the next least stable branch, and so on. Changes can be cherry-picked across branches, and the text files allow for simple diffs and patches that are easily reviewed.
Autobuild is the core consumer of config files in the Glazier system, but because the text files are based on the open YAML standard, administrators can implement new configuration parsers in any language or platform that they like.
One practical use of this is test frameworks: it is simple to write code which will consume configuration files for the sake of performing build testing or configuration auditing.
Another option is build simulation. Configs can be parsed and charted, graphed, or printed to observe their behavior when given arbitrary inputs, with no need to involve physical hardware or the delays inherent in performing an actual host installation.
Glazier relies heavily on HTTP(S) as its mechanism for the distribution of content. (We refer to HTTP and HTTPS interchangeably. However, HTTPS is required for Glazier to operate correctly.) HTTP was chosen for a variety of reasons, including:
In a Glazier environment, the web servers host nearly all content except for the initial boot media. This will include all configuration files, as well as binaries (installers, images, etc) and scripts. As Autobuild executes, it retrieves these files on demand.
It is up to the administrator to decide how exactly to structure the files within the web service, as well as how to deploy the files to the web service. In a test environment, the administrator may simply place and edit the files directly within the web host. In a production environment, it is recommended to develop a more formal “deployment” system; ideally, one which can synchronize content from a version control system directly to the web host.
Glazier is implemented in Python, which is free and cross-platform. Parts of Glazier does depend on Windows-specific functionality, such as WMI. This does not mean it cannot be ported to run from other OSes, however, this will require extra effort.
Python requires an interpreter to be available within the OS while Glazier is running. Python interpreters for Windows are freely available.
Glazier is not compiled code. Anyone can open Glazier’s Python files and edit them. This is one of the great strengths of Glazier: with a little knowledge of Python, you can easily extend Glazier with custom functionality.
When it comes to the act of imaging a system, most of Glazier’s time is spent performing Actions. Glazier ships with several core Actions, which are documented in the Actions README.
Adding new Glazier Actions is meant to be as simple as possible. Actions are automatically recognized by Autobuild’s configuration handler. An administrator need only drop a new Python class into the actions module, and the new command becomes immediately accessible for use in config files.
Action classes also expose an (optional) validation capability. This can be integrated with a unit test framework to provide real-time validation of configuration files.
Administrators may prefer to implement some parts of the imaging process in other languages, such as PowerShell, Batch, Go, etc. This is perfectly fine, fully supported, and in some cases even recommended.
As described above, Glazier’s Autobuild tool is essentially a command executor. It works great out of the box with companion scripts or executables and can recognize success or failure conditions based on return codes. For more complex interactions, custom Actions can easily wrap external scripts and executables.