Configuration Management (CM)

Configuration Management (CM) is a continuous process of recording and maintaining consistent and reliable records pertaining to an organization's hardware and software composition, including software version control and hardware updates.

Overview of Configuration Management Tools

Even though each CM tool has its own terms, philosophy and ecosystem, they typically share many characteristics and have similar concepts. Most configuration management tools use a controller/master and node/agent model. Essentially, the controller directs the configuration of the nodes, based on a series of instructions or tasks defined in your provisioning scripts. Below you can find the most common features present in most configuration management tools for servers:

• Automation Framework: Each CM tool provides a specific syntax and a set of features that you can use to write provisioning scripts. Most tools will have features that make their language similar to conventional programming languages, but in a simplified way. Variables, loops, and conditionals are common features provided to facilitate the creation of more versatile provisioning scripts.
• Idempotent Behavior: Configuration management tools keep track of the state of resources in order to avoid repeating tasks that were executed before. If a package was already installed, the tool won’t try to install it again. The objective is that after each provisioning run the system reaches (or keeps) the desired state, even if you run it multiple times. This is what characterizes these tools as having an idempotent behavior. This behavior is not necessarily enforced in all cases, though.
• System Facts: Configuration management tools usually provide detailed information about the system being provisioned. This data is available through global variables, known as facts. They include things like network interfaces, IP addresses, operating system, and distribution. Each tool will provide a different set of facts. They can be used to make provisioning scripts and templates more adaptive for multiple systems.
• Templating System: Most CM tools will provide a built-in templating system that can be used to facilitate setting up configuration files and services. Templates usually support variables, loops, and conditionals that can be used to maximise versatility. For instance, you can use a template to easily set up a new virtual host within Apache, while reusing the same template for multiple server installations. Instead of having only hard-coded, static values, a template should contain placeholders for values that can change from host to host, such as NameServer and DocumentRoot.
• Extensibility: Even though provisioning scripts can be very specialized for the needs and demands of a particular server, there are many cases when you have similar server setups or parts of a setup that could be shared between multiple servers. Most provisioning tools will provide ways in which you can easily reuse and share smaller chunks of your provisioning setup as modules or plugins. Third-party modules and plugins are often easy to find on the Internet, specially for common server setups like installing a PHP web server. CM tools tend to have a strong community built around them and users are encouraged to share their custom extensions. Using extensions provided by other users can save you a lot of time, while also serving as an excellent way of learning how other users solved common problems using your tool of choice.

Choosing a Configuration Management Tool

There are many CM tools available in the market, each one with a different set of features and different complexity levels. Popular choices include Chef, Ansible, and Puppet. The first challenge is to choose a tool that is a good fit for your needs. There are a few things you should take into consideration before making a choice:

• Infrastructure Complexity: Most configuration management tools require a minimum hierarchy consisting of a controller machine and a node that will be managed by it. Puppet, for example, requires an agent application to be installed on each node, and a master application to be installed on the controller machine. Ansible, on the other hand, has a decentralized structure that doesn’t require installation of additional software on the nodes, but relies on SSH to execute the provisioning tasks. For smaller projects, a simplified infrastructure might seem like a better fit, however it is important to take into consideration aspects like scalability and security, which may not be enforced by the tool. Some tools can have more components and moving parts, which might increase the complexity of your infrastructure, impacting on the learning curve and possibly increasing the overall cost of implementation.
• Learning Curve: CM tools provide a custom syntax, sometimes using a Domain Specific Language (DSL), and a set of features that comprise their framework for automation. As with conventional programming languages, some tools will demand a higher learning curve to be mastered. The infrastructure requirements might also influence the complexity of the tool and how quickly you will be able to see a return of investment.
• Cost: Most CM tools offer free or open source versions, with paid subscriptions for advanced features and services. Some tools will have more limitations than others, so depending on your specific needs and how your infrastructure grows, you might end up having to pay for these services. Training should also be considered a potential extra cost, not only in monetary terms, but also regarding the time that will be necessary to get your team up to speed with the tool you end up choosing.
• Advanced Tooling: Most tools offer paid services that can include support, extensions, and advanced tooling. It’s important to analyse your specific needs, the size of your infrastructure and whether or not there is a need for using these services. Management panels, for instance, are a common service offered by these tools, and they can greatly facilitate the process of managing and monitoring all your servers from a central point.
• Community and Support: A strong and welcoming community can be extremely resourceful for support and for documentation, since users are typically happy to share their knowledge and their extensions (modules, plugins, and provisioning scripts) with other users. This can be helpful to speed up your learning curve and avoid extra costs with paid support or training.