Tag Archives: how to install ansible

Installing Ansible and running the first command

How to install Ansible and how to run a simple command using Ansible.

Ansible installation

In this article, we will walk you through step by step procedure to install Ansible and then run the first ping command on its clients.

We will be using our lab setup built using containers for this exercise. In our all articles related to Ansible, we are referring Ansible server as Ansible control machine i.e. where Ansible software is installed and running. Ansible clients are machines who are being managed using this Ansible.

Pre-requisite

Ansible control machine requirements

It should be a Linux machine. Ansible can bot be installed on Windows OS. and secondly it should have Python installed.

It’s preferred to have passwordless SSH setup between Ansible control machine and managed machine for smooth executions but not mandatory.

Ansible managed machine requirement

It should have libselinux-python installed if SELinux is enabled which is obviously most of the time.

A Python interpreter should be installed.


Ansible installation

Installation of Ansible is an easy task. Its a package so install it like you install any other package in your Linux. Make sure you have subscribed to the proper repo which has an Ansible engine available to install.

I enabled EPEL repo on my Oracle Linux running in Virtual box and installed it using –

[root@ansible-srv ~]# yum install ansible

Once the installation is done, you need to add your client list in file /etc/ansible/hosts. Our setup files look like below :

[root@ansible-srv ~]# cat /etc/ansible/hosts
[all:vars]
ansible_user=ansible-usr

[webserver]
k-web1 ansible_host=172.17.0.9
k-web2 ansible_host=172.17.0.3

[middleware]
k-app1 ansible_host=172.17.0.4
k-app2 ansible_host=172.17.0.5

[database]
k-db1 ansible_host=172.17.0.6

Here, we defined the Ansible default user in the inventory file itself. Since we do not have DNS and using containers in our setup, I defined hostname and IP as mentioned above.


Running first Ansible command

As I explained earlier in the Lab setup article, I configured passwordless SSH from the Ansible control machine to the managed node.

Let’s run our first ansible command i.e. ping one hosts. Command syntax is – ansible -m <module> <target>

[root@ansible-srv ~]# ansible -m ping k-db1
k-db1 | SUCCESS => {
    "ansible_facts": {
        "discovered_interpreter_python": "/usr/bin/python3"
    },
    "changed": false,
    "ping": "pong"
}

We used the ping module here and the target host is k-db1. And we received back pong i.e. command successfully executed. In this output –

  • SUCCESS is command exit status
  • ansible_facts is data collected by Ansible while executing a command on the managed node.
  • changed indicates if the task has to make any changes

Let’s run another simple command like hostname

[root@ansible-srv ~]# ansible -m command -a hostname k-db1
k-db1 | CHANGED | rc=0 >>
k-db1

Here in the second line you see the command stdout i.e. output. and return code rc i.e. exit code of the command is 0 confirming command execution was successful.

Install Ansible in Linux

Small tutorial about how to install Ansible in Linux and run ansible command on the remote clients from the control server.

Ansible installation in Linux

What is Ansible ?

Ansible is an open-source configuration management tool developed by Red Hat. You can have enterprise support for it from Red Hat subscriptions. Ansible is written in Python, Ruby, and Power shell. It uses SSH in the background to communicate with clients and execute tasks. The best feature of Ansible is being agent-less hence no load on clients and configurations can be pushed from the server at any time.

Ansible installation

The first pre-requisite of Ansible is: Primary or control server should have password-less SSH connection configured for Ansible user for all its client servers. You can configure passwordless SSH in two commands steps using ssh-keygen and ssh-copy-id.

For our understanding, we have 1 control server kerneltalks1 and 1 client kerneltalks2 and we have configured passwordless SSH for user shrikant (which we treat as Ansible user here)

Lets install Ansible on control server i.e. kerneltalks1

Ansible can be installed using the normal package installation procedure. Below are quick commands for your reference.

  • RHELsubscription-manager repos --enable rhel-7-server-ansible-2.6-rpms; yum install ansible
  • CentOS, Fedora : yum install ansible
  • Ubuntuapt-add-repository --yes --update ppa:ansible/ansibleapt-get install ansible
  • Git clone : git clone https://github.com/ansible/ansible.git
    • cd ./ansiblemake rpm
    • rpm -Uvh ./rpm-build/ansible-*.noarch.rpm

I installed Ansible on my CentOS machine using above command.

[root@kerneltalks1 ~]# ansible --version
ansible 2.7.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /bin/ansible
  python version = 2.7.5 (default, Aug  4 2017, 00:39:18) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)]

Ansible default config structure

After installation, Ansible creates/etc/ansible directory with default configuration in it.  You can find ansible.cfg and hosts files in it.

[root@kerneltalks1 ~]# ll /etc/ansible
total 24
-rw-r--r--. 1 root root 20269 Oct  9 01:34 ansible.cfg
-rw-r--r--. 1 root root  1016 Oct  9 01:34 hosts
drwxr-xr-x. 2 root root     6 Oct  9 01:34 roles

ansible.cfg is default configuration file for ansible executable

hosts is a list of clients on which control server executes commands remotely via password-less SSH.

Running first command via Ansible

Let’s configure kerneltalks2 and run our first Ansible command on it remotely from kerneltalks1 control server.

You need to configure the password less ssh as we discussed earlier. Then add this server name in /etc/ansible/hosts file.

root@kerneltalks1 # cat /etc/ansible/hosts
[testservers]
 172.31.81.83 

Here IP mentioned is of kerneltalks2 and you can specify the grouping of servers in square braces. And you are good to go. Run ansible command with ping module (-m switch). There are many modules comes in-built with ansible which you can use rather than using equivalent shell commands.

[shrikant@kerneltalks1 ~]$ ansible -m ping all
172.31.81.83 | SUCCESS => {
    "changed": false,
    "ping": "pong"
}

You can see the output is a success on the mentioned IP. So we installed and ran the first successful command using ansible!

Common errors

1. If you try to run ansible command on a group of the server which does not exist in the host file. You will see below error –

[shrikant@kerneltalks1 ~]$ ansible -m ping testserver
 [WARNING]: Could not match supplied host pattern, ignoring: testserver

 [WARNING]: No hosts matched, nothing to do

You need to check /etc/ansible/hosts file (or hosts files being referred by your ansible installation) and make sure the server group mentioned on command exists in it.

2. If you do not configure passwordless SSH from the control server to the client or If the client is not reachable over the network you will see below error.

[root@kerneltalks1 ansible]# ansible -m ping all
kerneltalks2 | UNREACHABLE! => {
    "changed": false,
    "msg": "Failed to connect to the host via ssh: Warning: Permanently added 'kerneltalks2,172.31.81.83' (ECDSA) to the list of known hosts.\r\nPermission denied (publickey,gssapi-keyex,gssapi-with-mic,password).\r\n",
    "unreachable": true
}

You need to check the connectivity and passwordless ssh access from the control server.