Ansible inventories, Ad-Hoc commands and first playbook

Hi folks,

Welcome to our first post in this one we will be talking about ansible, installation, inventories, ad-hoc commands and a basic playbook, everything will be technical (less theory). Invetories are the base of running ansible playbooks and Ad-Hoc commands.

Installation

We will be using Centos 7 during this post.

$cat /etc/redhat-release

CentOS Linux release 7.2.1511 (Core)

If you are using an earlier release you will need to install epel release (Extra Packages for Enterprise Linux) by executing below command:

 $sudo yum -y install epel-release

Then to list all repositories with yum to confirm it was installed

$yum repolist

If not, we can continue here:
To make sure let's execute next command to verify if ansible is in our repository

$yum list | grep ansible

ansible.noarch                       2.1.1.0-1.el7          epel

ansible-inventory-grapher.noarch     1.0.1-2.el7            epel

ansible-lint.noarch                  3.1.3-1.el7            epel

ansible-openstack-modules.noarch     0-20179d751a.el7       epel

ansible1.9.noarch                    1.9.6-2.el7            epel

kubernetes-ansible.noarch            0.6.0-0.1.ebd5.el7     epel

In this case will be installing latest version (2.1) by executing:

$yum -y install ansible

 ** Remember to install we need to have enough privileges.

To confirm it was successfully installed execute:

$ansible --version
  ansible 2.1.0.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = Default w/o overrides

Ansible inventories

Imagine we have below Virtual Machines (for now on VM)

vmdbmongodb01
vmdbmongodb02
vmdbmysql01
vmdbmysql02
vmdbpostgresql01
vmdbpostgresql02
vmdev01
vmdhcp01
vmemail01
vmemail02
vmnagios01
vmnagios02
vmweb01
vmweb02
vmweb03
vmweb04
vmweb05

Basic ansible inventory's structure
We will create a basic inventory using the above list with a title between square brakets []
Our first inventory is completed :D

$cat hosts
[my_servers]
vmdbmongodb01
vmdbmongodb02
vmdbmysql01
vmdbmysql02
vmdbpostgresql01
vmdbpostgresql02
vmdev01
vmdhcp01
vmemail01
vmemail02
vmnagios01
vmnagios02
vmweb01
vmweb02
vmweb03
vmweb04
vmweb05

Inventory divided depending on its function
As we all know every server has a different role, so we need to apply different configuration, ACL's and/or  install different applications depending on its rol, as shown below; servers are grouped by rol:

$cat hosts
[mongo_servers]
vmdbmongodb01
vmdbmongodb02

[mysql_servers]
vmdbmysql01
vmdbmysql02

[postgres_servers]
vmdbpostgresql01
vmdbpostgresql02

[dev_servers]
vmdev01

[dhcp_servers]
vmdhcp01

[mail_servers]
vmemail01
vmemail02

[nagios_servers]
vmnagios01
vmnagios02

[web_servers]
vmweb01
vmweb02
vmweb03
vmweb04
vmweb05

Tips and tricks
Ansible is a powerful configuration management tool, we can use regex to create our inventories, let's improve above inventory.

$cat hosts
[mongo_servers]
vmdbmongodb[01:02]

[mysql_servers]
vmdbmysql[01:02]

[postgres_servers]
vmdbpostgresql[01:02]

[dev_servers]
vmdev01

[dhcp_servers]
vmdhcp01

[mail_servers]
vmemail[01:02]

[nagios_servers]
vmnagios[01:02]

[web_servers]
vmweb[01:05]

Note this inventory will work as good as the one above, When we have thousands of servers will save thousand of lines. e.g. what about if we have from vmserver01 to vmserver150. we can reduce it as
shown below (we will be saving 149 lines, it will make inventory easier to read)

[my_thousand_servers]
vmserver[01:150]

Also if we are using a domain on vmserver servers we can use:

[my_thousand_servers]
vmserver[01:150].mydomain.com

Ad-Hoc commands

This is the first ad-hoc command we are executing and is divided as follows :

ansible Command to execute (obviously)

mongo_servers The part of the inventory we want to execute (from ansible default location, if you would like to execute another inventory just add -i /example/path/my_inventory)

-m ping Standard for  module and ping is the module we are invoking

--ask-pass This line will ask us for our password (the one we use to get into the servers)

If our command is executed as below, It will trigger errors due to it does not have right privileges to get into those servers (It is not the same ping ansible module that ping linux command!!!)

ansible mongo_servers -m ping

After creating my key and copying to those servers it works fine

ssh-keygen -t rsa

ssh-copy-id vmdbmongodb01

ssh-copy-id vmdbmongodb02

We can execute it many ways, for example, using

-u User to exectue command as (sorea)

--private-key Path where the selectioned user's key is located

On the underlined part is taken by default the sorea's keys

Note: This last pasrt is being executed with a different user (root) 

First playbook

This playbook is to install mongodb package using ansible yum module, for achieve this step we use below page as reference:

https://docs.mongodb.com/manual/tutorial/install-mongodb-on-red-hat/#packages

As pre-step we needed to create a new repo using ansible yum module due to all mongodb packages are located there:

Below playbooks can be found in:
https://github.com/soreaort/all-it/tree/master/ansible/mongdb_installation

$ cat create_mongodb_repo.yml

---

- name: Create MongoDB repo mongodb-org-3.2

  hosts: mongo_servers

  become: yes

  become_user: root

  tasks:

    - name: Creating repo

      yum_repository:

       name: MongoDB-mongodb-org-3.2

       description: mongodb-org-3.2

       baseurl: https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.2/x86_64/

       gpgcheck: yes

       enabled: yes

       gpgkey: https://www.mongodb.org/static/pgp/server-3.2.asc

And was executed as follows: (by default using our keys)

$ ansible-playbook create_mongodb_repo.yml

The main playbook is to install mongodb-org package from mongodb repository (already created)

$ cat install_mongodb.yml

---

- name: Install and enable MongoDB

  hosts: mongo_servers

  become: yes

  become_user: root

  tasks:

    - name: Installing MongoDB

      yum: name=mongodb-org state=present enablerepo=MongoDB-mongodb-org-3.2

    - name: Staring and enabling MongoDB

      service: name=mongod state=started enabled=yes

Executed as:
$ ansible-playbook install_mongodb.yml

Final step is validating everything is working fine on target servers:

[sorea@vmdbmongodb02 ~]$ service mongod status