Learning Puppet - II: Applying Classes

In my previous post about learning Puppet, I left a few open questions that I will attempt to answer as I continue learning.

1. How can I apply Puppet classes?
2. How can I install modules?
3. How can I define functions in Puppet?

In the last post, I was unable to apply a class so I moved ahead without it. Let us look at that in this post.

To apply a class, I created a module, created its init.pp file and added a class in it.

Let us consider the module name to be mod. The init.pp will be located at mod/manifests/init.pp. I just keep it empty to begin with. The name of the class in that file has to match the module name though.

class mod{
}

Moving on to create a class of interest, let us add one to install Openjdk. The file would be mod/manifests/jdk.pp.

class mod::jdk () {
  notice("Installing openJDK")
  # Install java
  package { 'openjdk':
    ensure => installed,
    name => 'java-1.8.0-openjdk-headless',
    alias => 'openjdk',
  }
}

To apply the manifest, the command would be as follows:

puppet apply --modulepath=/path/to/parent/of/module -e "include mod::jdk"

Finding where a package is installed

Recently, I faced an issue on a CentOS box where I had to find the location of a package. My application was running on it and I wanted to modify its config. I was unable to pick the config in /etc so I figured it must be in the folder in which the application is installed.

The application was installed as a daemon but it seems the PATH was not updated. I searched in the usual locations of binaries and packages but I could not find it. The only option left for me was to find out where it was installed.

Using the following command showed all the files of the application package.

rpm -ql <my application>

From the list, I could see where my config file was placed during install.

Increasing the maximum number of file descriptors allowed per user on Cent OS 6

For some applications like elasticsearch, the maximum number of file descriptors needs to quite high. The way of modifying the value varies from distro to distro. In Cent OS6, the following did not work.

1. Using sysctl as root
sysctl -w fs.file-max=100000

2. Using ulimit as root

After the above approaches, when you check the value using the following, the value will show up.

cat /proc/sys/fs/file-max

However, setting the values as root, does not change the values for other regular users. To set it specifically for any user, change the value in /etc/security/limits.conf file. Setting only the soft or hard limit will not be sufficient. Therefore, the following lines should be added.

<user> soft nofile <value>

<user> hard nofile <value>

After the modifications, it is required to logout and log back into the system.