Paras - Ansible/Puppet/Terraform

Ansible_Documentation

Tasks and hosts

Ansible runs tasks on hosts, and all you need is SSH. In other words, Ansible runs in one place (your laptop, or a deploy box like Rundeck or Tower, or somewhere else), opens up SSH connections to your remote hosts and then runs commands directly on them.

What is a task?

A task can be anything from creating a bucket in AWS S3, to launching an instance in Azure, installing pip on a server, updating a config file, or simply checking the time on a remote host. In this tutorial we focus on tasks to configure a remote Ubuntu host.

For example, this task installs pip on Ubuntu:

- name: ensure pip is installed

    apt:

      name: python-pip

      state: installed

Every task uses a module. Here we use the apt module, a wrapper for the apt package manager, letting you specify what to do in YAML syntax. There are hundreds of different modules included in Ansible.

What is a host?

The host is where the tasks get run. It can be any number of remote hosts that you have SSH access to, or localhost.

Your hosts respective IP addresses or hostnames need to be stored in an inventory file for Ansible to be aware of them. Later when you run Ansible, you will specify one or more hosts, or groups of hosts, defined in the inventory file.

Ansible_Documentation

Creating an inventory

In this tutorial you have access to one host named host01. To let Ansible know about it, put its hostname in an inventory file. Let's call our inventory myhosts, with one group called group1.

echo "[paras]" > myhosts

Then add the host to the group:

echo "host01 ansible_ssh_user=ubuntu" >> myhosts

Here we're also passing the username to use for SSH access, as an inventory parameter.

Running Ansible

Ad-hoc Tasks

To run an ad-hoc task, using a single module, use ansible.

For example, to check the current date and time of the remote host:

ansible paras-i myhosts -m command -a date

(if the command fails the first time, try again in few seconds, as the test host may not yet have been provisioned)

group1 = group to run against. You can also use the name of an individual host, so host01 would work just as well for this example.
myhosts = name of the inventory file listing all available hosts
command = module to use (the command module returns the result of a bash command)
date = argument for the module, in this case a standard shell command date.

When you run the command above, Ansible establishes an SSH connection with the remote host, executes the command, captures the output and returns it.

$ ansible paras -i myhosts -m ping

host01 | success >> {

"changed": false,

"ping": "pong"

}

Running a playbook

Playbook

A playbook is an entirely different way of running Ansible, that is far more powerful.

What is a play?

A play is a set of tasks mapped to a set of hosts. Plays are organised inside a text file called a playbook.

Running a playbook

This playbook runs one task, on our one host, host01. Note the indentation - it's important for how the file gets parsed. Blank lines are ignored, but makes the playbook more readable for humans.

---

- hosts: host01

    become: true

    tasks:

      - name: ensure latest sysstat is installed

        apt:

          name: sysstat

          state: latest

The above code is already in a file called site.yml. Let's check the contents:

cat site.yml

To run the playbook, use the ansible-playbook command with the inventory file myhosts:

ansible-playbook -i myhosts site.yml

Ansible should return the result 'Changed=1', indicating that the package was installed.

Playbook breakdown

What happened here?

--- denotes the beginning of a YAML file
hosts: host tells Ansible to run the tasks on the host host
become: true makes all your tasks run as sudo
- name: is basically a comment, describing what the task does
apt: specifies the module we want to use
name: is an argument to the apt module, that specifies the name of the package to install.

To see all arguments for a specific module, allowed values, and other details, you can use the CLI documentation that is included with Ansible:

ansible-doc apt

To close the documentation, enter q in the terminal.

NOTE: This tutorial is using Ubuntu. If your own hosts are RHEL/CentOS, you should use the yum module instead.

Ansible ensures

A fundamental principle of Ansible is that it ensures a desired state.

From the previous example:

- name: ensure latest sysstat is installed

    apt:

      name: sysstat

      state: latest

This tells Ansible to check if the latest version of sysstat is installed. If it is, Ansible will do nothing more, since the "latest" state is already achieved. If sysstat is not already there, or of an older version than what is available, Ansible installs the latest version.

If you run the playbook again, Ansible does the former, and instead of "Changed: 1", you will get "OK: 2, Changed 0". Try it out:

ansible-playbook -i myhosts site.yml

Ensure a package is removed

The apt module allows you to specify the state you wish the package to be in. If you want a specific version, you append it to the package name, for example:

- name: ensure sysstat is installed at version 10.2.0-1

    apt:

      name: sysstat=10.2.0-1

      state: installed

If you want to ensure that the package is not installed, you can declare that with state: absent, and Ansible will ensure it.

Update the playbook to remove sysstat.

sed -i -e 's/state: latest/state: absent/' -e 's/ensure.*/ensure sysstat is removed/' site.yml

Then re-run the playbook:

ansible-playbook -i myhosts site.yml

In summary, the same playbook should always be able to run on a host and - assuming there are no errors - produce exactly the desired state, regardless of what state the host started in. For example, should your playbook halt halfway through due to a network error, it would still finish successfully when you re-run it.

Install Docker using Ansible on remote hosts

$ ansible group1 -i myhosts -m systemd -a "name=docker-ce state=started" -m apt -a "name=dockerstate=present" -b

host01 | success >> {

"changed": true,

"stderr": "",

"stdout": "Reading package lists...\nBuilding dependency tree...\nReading state information...\nThe following package was automatically installed and is no longer required:\n libsensors4\nUse 'apt-get autoremove' to remove it.\nThe following NEW packages will be installed:\n docker\n0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.\nNeed to get 12.2 kB of archives.\nAfter this operation, 65.5 kB of additional disk space will be used.\nGet:1 http://archive.ubuntu.com/ubuntu/ trusty-updates/universe docker amd64 1.5-1 [12.2 kB]\nFetched 12.2 kB in 0s (54.7 kB/s)\nSelecting previously unselected package docker.\n(Reading database ... 57453 files and directoriescurrently installed.)\nPreparing to unpack .../docker_1.5-1_amd64.deb ...\nUnpacking docker (1.5-1) ...\nProcessing triggers for man-db (2.6.7.1-1ubuntu1) ...\nSetting up docker (1.5-1) ...\n"

}

ansible group1 -i myhosts -m command -a "docker ps"

host01 | success | rc=0 >>

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES

Now create a playbook to install Docker on the remote hosts

$ ansible-playbook -i myhosts create_docker_container.yml

PLAY [host01] *****************************************************************

GATHERING FACTS ***************************************************************

ok: [host01]

TASK: [create docker image] ***************************************************

changed: [host01]

PLAY RECAP ********************************************************************

host01 : ok=2 changed=1 unreachable=0 failed=0

$ ansible group1 -i myhosts -m command -a "docker ps"

host01 | success | rc=0 >>

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES

cb83ff9b8d08 jenkins/jenkins "/sbin/tini -- /us..." 21 seconds ago Up 21 seconds 50000/tcp, 0.0.0.0:8090->8080/tcp valaxy_demo

$ cat create_docker_container.yml

---

- hosts: host01

become: true

tasks:

- name: create docker image

shell: docker run -d --name valaxy_demo -p 8090:8080 jenkins/jenkins

Ansible Vs Puppet - What is the difference between Ansible and Puppet

This is one of the common DevOps interview questions. What is the difference between Ansible and Puppet? When will you choose Ansible over Puppet?

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