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Puppet – Coding Style ”; Previous Next In Puppet, the coding style defines all the standards which one needs to follow while trying to convert the infrastructure on the machine configuration into a code. Puppet works and performs all its defined tasks using resources. Puppet’s language definition helps in specifying all the resources in a structured way, which is required to manage any target machine that needs to be managed. Puppet uses Ruby as its encoding language, which has multiple inbuilt features that makes it very easy to get things done with a simple configuration on the code side. Fundamental Units Puppet uses multiple fundamental coding styles which is easy to understand and manage. Following is a list of few. Resources In Puppet, resources are known as fundamental modeling unit which are used to manage or modify any target system. Resources cover all the aspects of a system such as file, service, and package. Puppet comes with an in-built capability wherein it allows the users or developers to develop custom resources, which help in managing any particular unit of a machine In Puppet, all the resources are aggregated together either by using “define” or “classes”. These aggregation features help in organizing a module. Following is a sample resource which consists of multiple types, a title, and a list of attributes with which Puppet can support multiple attributes. Each resource in Puppet has its own default value, which could be overridden when required. Sample Puppet Resource for File In the following command, we are trying to specify a permission for a particular file. file { ”/etc/passwd”: owner => superuser, group => superuser, mode => 644, } Whenever the above command gets executed on any machine, it will verify that the passwd file in the system is configured as described. The file before: colon is the title of resource, which can be referred as resource in other parts of Puppet configuration. Specifying Local Name in Addition to the Title file { ”sshdconfig”: name => $operaSystem ? { solaris => ”/usr/local/etc/ssh/sshd_config”, default => ”/etc/ssh/sshd_config”, }, owner => superuser, group => superuser, mode => 644, } By using the title, which is always the same it is very easy to refer file resource in configuration without having to repeat the OS related logic. Another example could be using a service that depends on a file. service { ”sshd”: subscribe => File[sshdconfig], } With this dependency, the sshd service will always restart once the sshdconfig file changes. The point to be remember here is File[sshdconfig] is a declaration as File as in lower case but if we change it to FILE[sshdconfig] then it would have been a reference. One fundamental point that one needs to keep in mind while declaring a resource is, it can be declared only once per config file. Repeating declaration of the same resource more than once will cause an error. Through this fundamental concept, Puppet makes sure that the configuration is well modeled. We even have the capability to manage resource dependency which helps is managing multiple relationships. service { ”sshd”: require => File[”sshdconfig”, ”sshconfig”, ”authorized_keys”] } Metaparameters Metaparameters are known as global parameters in Puppet. One of the key features of metaparameter is, it works with any type of resource in Puppet. Resource Default When one needs to define a default resource attribute value, Puppet provides a set of syntax to archive it, using a capitalized resource specification that has no title. For example, if we want to set the default path of all the executable it can be done with the following command. Exec { path => ”/usr/bin:/bin:/usr/sbin:/sbin” } exec { ”echo Testing mataparamaters.”: } In the above command, the first statement Exec will set the default value for exec resource. Exec resource requires a fully qualified path or a path which looks like an executable. With this, one can define a single default path for the entire configuration. Defaults work with any resource type in Puppet. Defaults are not global values, however, they only affect the scope in which they are defined or the very next variable to it. If one wants to define default for a complete configuration, then we define the default and the class in the very next section. Resource Collections Aggregation is method of collecting things together. Puppet supports a very powerful concept of aggregation. In Puppet, aggregation is used for grouping resource which is the fundamental unit of Puppet together. This concept of aggregation in Puppet is achieved by using two powerful methods known as classes and definition. Classes and Definition Classes are responsible for modeling the fundamental aspects of node. They can say node is a web server and this particular node is one of them. In Puppet, programming classes are singleton and they can get evaluated once per node. Definition on the other hand can be used many times on a single node. They work similarly as one has created his own Puppet type using the language. They are created to be used multiple times with different input each time. This means one can pass variable values into the definition. Difference between Class and Definition The only key difference between a class and definition is while defining the building structure and allocating resources, class gets evaluated only once per node, wherein on the other hand, a definition is used multiple times on the same single node. Classes Classes in Puppet are introduced using the class keyword and the content of that particular class is wrapped inside the curly braces as shown in the following example. class unix { file { ”/etc/passwd”: owner => ”superuser”, group => ”superuser”, mode => 644; ”/etc/shadow”: owner => ”vipin”, group => ”vipin”, mode => 440; } } In the following example, we have used some short hand which is similar to the above. class unix { file { ”/etc/passwd”: owner => ”superuser”, group => ”superuser”, mode => 644; } file {”/etc/shadow”: owner => ”vipin”, group => ”vipin”, mode => 440; }