Open Source For You — December 2017

Admin How To

34 | DECEMBER 2017 | OPEN SOURCE FOR YOU | http://www.OpenSourceForU.com

Installing and working with Molecule is simple. Follow

the steps shown below. First, get the OS updated as follows:

sudo apt-get update && sudo apt-get -y upgrade

Next, install Docker:

sudo apt install docker.io

Now install Molecule with the help of Python Pip:

sudo apt-get install python-pip python-dev build-essential

sudo pip install --upgrade pip

sudo pip install molecule

After the install, do a version check of Molecule. If the

molecule version is not the latest, upgrade it as follows:

sudo pip install --upgrade molecule

It is always good to work with the latest version of

Molecule as there are significant changes compared to an

earlier version. Enabling or disabling modules in the latest

version of Molecule is more effective. For example, a common

problem faced is the forced audit errors that make Molecule

fail. When starting to test with Molecule, at times audit errors

can pose a roadblock. Disabling the Lint module during the

initial phase can give you some speed to concentrate on writing

tests rather than trying to fix the audit errors.

Here are a few features of Molecule explained, though the

full toolset offers more.

1. Create: This creates a virtualised provider, which in our
   case is the Docker container.


2. Converge: Uses the provisioner and runs the Ansible
   scripts to the target running Docker containers.


3. Idempotency: Uses the provisioner to check the
   idempotency of Ansible scripts.


4. Lint: This does code audits of Ansible scripts, test code,
   test scripts, etc.


5. Verify: Runs the test scripts written.


6. Test: Runs the full steps needed for Molecule, i.e., create,
   converge, Lint, verify and destroy.
   The roles need to be initialised by the following command:

molecule init role –role-name abc

This will create all the folders needed to create the role,

and is similar to the following command:

ansible-galaxy init abc

There are certain differences in the directory structure,

and some amount of manual folder creation may be

required.

Table 1: A comparison of folders created by Ansible and Molecule

Folders creat-

ed by Ansible-

galaxy init

Folders

created by

Molecule init

Remarks

Default Default No changes are

needed and folder

Handler Handler structure is identical

Meta Meta

README.md README.md

Tasks Tasks

Vars Vars

Files Files Folders needs to be

created manually

to take advantage

of file and template

module of ansible

templates templates

molecule All Molecule related

scripts and test

scripts are placed in

this folder

The Molecule folder has files in which one can put

in a pre-created Molecule playbook and test scripts. The

environment that is created is named default. This can be

changed as per the project’s requirements.

One file that will be of interest is molecule.yml, which

is placed at:

./molecule/default/molecule.yml

Another file which describes the playbook for the role is

playbook.yml placed at:

./molecule/default/playbook.yml

Note: Molecule initialises the environment called

default but engineers can use a name as per the

environment used in the project.

Figure 1: molecule.xml sample file