Managing Packages

Package management is a critical task for any system administrator. In this tutorial we will show you how easy it is to install, manage and remove packages using CFEngine. Please note that this guide assumes you are using CFEngine 3.7.0 or a later version.

As a first example, we will use CFEngine to update OpenSSL, which is timely given the recent disclosure of the Heartbleed vulnerability. If we simply want to make sure the latest version of OpenSSL is installed in all our hosts, we can use the packages promise type, like this:

body common control
{
      inputs => { "$(sys.libdir)/stdlib.cf" };
      bundlesequence => { "manage_packages" };
}

bundle agent manage_packages
{
packages:
  "openssl"
    policy => "present",
    version => "latest",
    package_module => yum;
}

The package_module promise attribute tells CFEngine which package manager we want to use. Defaults can be set up by using the package_module common control attribute. When we run this on an CentOS 6 system, we can verify the openssl version before and after running the policy, and we get the following output:


# yum list installed | grep openssl
openssl.x86_64          1.0.0-27.el6    @anaconda-CentOS-201303020151.x86_64/6.4
openssl-devel.x86_64    1.0.0-27.el6    @anaconda-CentOS-201303020151.x86_64/6.4
# cf-agent -K ./manage_packages.cf
# yum list installed | grep openssl
openssl.x86_64          1.0.1e-42.el6   @base                                   
openssl-devel.x86_64    1.0.1e-42.el6   @base         

Additionally, you may want to make sure certain packages are not installed on the system. On my CentOS 6 system, I can see that the telnet package is installed.


# yum list installed | grep telnet
telnet.x86_64           1:0.17-48.el6   @base 
# which telnet
/usr/bin/telnet

Making sure this package is removed from the system is easy: adding one more promise to our previous policy, this time using the absent policy:


bundle agent manage_packages
{
packages:
  "openssl"
    policy => "present",
    version => "latest",
    package_module => yum;

  "telnet"
    policy => "absent",
    package_module => yum;
}

Note that we leave the previous line in place. This way, CFEngine will continue to ensure that the openssl package is always updated to its latest version. We can now see the policy in action:


# cf-agent -K ./manage_packages.cf
# yum list installed | grep telnet
# which telnet
/usr/bin/which: no telnet in (/sbin:/bin:/usr/sbin:/usr/bin:/var/cfengine/bin)

The packages promise also supports version pinning, so that you can specify exactly the version you want to have installed. It is modular and extensible, so that it is easy to add support for new platforms and package managers. For complete documentation, please have a look at the reference manual for the packages promise.

Of course, running the policy by hand is only good for initial testing. Once your policy works the way you need, you will want to deploy it to your entire infrastructure by integrating your policy into your regular cf-agent execution, thus making sure that the desired state of your packages is always kept automatically on all your machines. To do so, you need to do the following:

Remove the “body common control” declaration from manage_packages.cf.
Copy manage_packages.cf to /var/cfengine/masterfiles/ in your policy hub.
In /var/cfengine/masterfiles/promises.cf, add “manage_packages.cf” to the inputs declaration, and “manage_packages” to the bundlesequence declaration.

Run cf-promises on your hub to verify that there are no errors in your promises.cf file.
Wait a few minutes for the new policy to propagate and start taking effect in your entire infrastructure. This is where the real power of CFEngine becomes apparent! With few changes in a single place, you can control the desired state of your entire infrastructure, whether it’s composed of a few or many thousands of machines.

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