Ansible is a very simple, clean and elegant tool to provision your production or development machines. It can be also used to setup and configure your development desktop, for example from a plain Ubuntu 14.04 LTS installation. For this task, we will soon run into the need to check, download and install applications as .deb packages because there is no ppa repository available (e.g. for dropbox, vagrant, etc.). In this blogpost, I will discribe how I solved this problem using Ansible.

## Checking if .deb Package is already installed

We want to install the package my_package - so first, we need to make sure that it is not yet already installed. We will use the bash command dpkg-query -W my_package to check for the availability of the package. We also want to register the output of this command - which can be done with the register statement in Ansible - in order to use the output as a conditional statement for other tasks.

In the above code, I added the failed_when statement, to not let the command fail when it exits with an error code 1 - which means the package was not found. Additionally, we set the changed_when statement, to return the state changed only when the package is not found.

## Downloading and installing a .deb package

Once we know that a package is not yet installed, we want to download and install it. To do so, we will use the 2 variables my_package_url and my_package_name that we need to register somewhere (preferably in the vars/ directory of the current role) and the get_url module from Ansible. We solely want to download the file, if it is not already installed - which we can check with the when statement and the previously registered vagrant_check_deb variable. We can check the return code from a registered command by using the .rc attribute.

Finally, we install the package - again just if the package was not previously installed.

## Further Readings

This technique is used in my project dev-env, a Ansible based installer for a local development environment. The source code of this project and the complete Ansible configuration and roles can be found on GitHub.