{"id":724,"date":"2018-06-05T13:19:43","date_gmt":"2018-06-05T13:19:43","guid":{"rendered":"https:\/\/www.nicktailor.com\/?p=724"},"modified":"2020-06-17T07:37:32","modified_gmt":"2020-06-17T07:37:32","slug":"how-to-setup-ansible-on-centos-7","status":"publish","type":"post","link":"https:\/\/nicktailor.com\/tech-blog\/how-to-setup-ansible-on-centos-7\/","title":{"rendered":"How to setup ansible on centos 7"},"content":{"rendered":"

Prerequisites<\/span><\/p>\n

To follow this tutorial, you will need:<\/span><\/p>\n

Step 1 \u2014 Installing Ansible<\/span><\/p>\n

To <\/span>begin exploring Ansible as a means of managing our various servers, we need to install the Ansible software on at least one machine.<\/span><\/p>\n

To get Ansible for CentOS 7, first ensure that the CentOS 7 EPEL repository is installed:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>sudo<\/span> yum install <\/span>epel<\/span>-release<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

Once the repository is installed, install Ansible with\u00a0<\/span>yum<\/span>:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>sudo<\/span> yum install ansible<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

We now have <\/span>all of<\/span> the software required to administer our servers through Ansible.<\/span><\/p>\n

Step 2 \u2014 Configuring Ansible Hosts<\/span><\/p>\n

Ansible keeps track of <\/span>all of<\/span> the ser<\/span>vers that it knows about through a “hosts” file. We need to set up this file first before we can begin to communicate with our other computers.<\/span><\/p>\n

Open the file with root privileges like this:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>sudo<\/span> vi \/etc\/ansible\/hosts<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

You will see a file that has a lot <\/span>of example configurations commented out. Keep these examples in the file to help you learn Ansible’s configuration if you want to implement more complex scenarios in the future.<\/span><\/p>\n

The hosts file is <\/span>fairly flexible<\/span> and can be configured in a few different way<\/span>s. The syntax we are going to use though looks something like this:<\/span><\/p>\n

Example hosts file<\/span><\/p>\n

[<\/span>group_name<\/span>]<\/span><\/p>\n

alias <\/span>ansible_ssh_host<\/span>=<\/span>your_server_ip<\/span><\/p>\n

The\u00a0<\/span>group_name<\/span>\u00a0is an organizational tag that lets you refer to any servers listed under it with one word. The <\/span>alias is just a name to refer to that server.<\/span><\/p>\n

Imagine you have three servers you want to control with Ansible. Ansible communicates with client computers through SSH, so each server you want to manage should be accessible from the Ansible server by typing:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ssh<\/span> root@<\/span>your_server_ip<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

You should not be prompted for a password. While Ansible certainly has the ability to handle <\/span>password-based<\/span> SSH authentication, SSH keys help keep things simple.\u00a0<\/span><\/p>\n

We will assume that our servers’ IP addresses are\u00a0<\/span>192.168.0.1<\/span>,\u00a0<\/span>192.168.0.2<\/span>, and\u00a0<\/span>192.168.0.3<\/span>. <\/span>Let’s<\/span> set this up so that we can refer to these individually as\u00a0<\/span>host1<\/span>,\u00a0<\/span>host2<\/span>, and\u00a0<\/span>host3<\/span>, or as a group as\u00a0<\/span>servers<\/span>. To configure this, you would add this block to your hosts file:<\/span><\/p>\n

\/etc\/ansible\/hosts<\/span><\/p>\n

[servers]<\/span><\/p>\n

host1 <\/span>ansible_ssh_host<\/span>=<\/span>192.168.0.1<\/span><\/p>\n

host2 <\/span>ansible_ssh_host<\/span>=<\/span>192.168.0.2<\/span><\/p>\n

host3 <\/span>ansible_ssh_host<\/span>=<\/span>192.168.0.3<\/span><\/p>\n

 <\/p>\n

Hosts can be in multiple groups and groups can configure parameters for <\/span>all of<\/span> their members. <\/span>Let’s<\/span> try this out now.<\/span><\/p>\n

Ansible will, by default, try to connect to remote hosts using your curr<\/span>ent username. If that user <\/span>doesn’t<\/span> exist on the remote system, a connection attempt will result in this error:<\/span><\/p>\n

Ansible connection error<\/span><\/p>\n

host1 | UNREACHABLE! => {<\/span><\/p>\n

“changed”: false,<\/span><\/p>\n

“<\/span>msg<\/span>“: “Failed to connect to the host via <\/span>ssh<\/span>.”,<\/span><\/p>\n

“unreachable”: <\/span>true<\/span><\/p>\n

}<\/span><\/p>\n

Let’s<\/span> specifically tell Ansible that it should connect to servers in the “servers” group with the nick<\/span>\u00a0user. Create a directory in the Ansible configuration structure called\u00a0<\/span>group_vars<\/span>.<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>sudo<\/span> mkdir<\/span> \/etc\/ansible\/<\/span>group_vars<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

Within this folder, we <\/span>can create YAML-formatted files for each group we want to configure:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>sudo<\/span> nano \/etc\/ansible\/<\/span>group_vars<\/span>\/servers<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

Add this code to the file:<\/span><\/p>\n

\/etc\/ansible\/<\/span>group_vars<\/span>\/servers<\/span><\/p>\n

—<\/span><\/p>\n

ansible_ssh_user<\/span>: ansible<\/strong>nick<\/strong><\/span><\/p>\n

YAML files start with “—“, so make sure you <\/span>don’t<\/span> forget that part.<\/span><\/p>\n

Save and close this file when you are finished. Now Ansible will always use the ansiblenick<\/strong><\/span>\u00a0user for the\u00a0<\/span>servers<\/span>\u00a0group, regardless of the current user.<\/span><\/p>\n

If you want to specify configuration details for every server, regardless of group <\/span>association, you can put those details in a file at\u00a0<\/span>\/etc\/ansible\/<\/span>group_vars<\/span>\/all<\/span>. Individual hosts can be configured by creating files under a directory at\u00a0<\/span>\/etc\/ansible\/<\/span>host_vars<\/span>.<\/span><\/p>\n

Step 3 \u2014 Using Simple Ansible Commands<\/span><\/p>\n

Now that we have our hosts set up and <\/span>enough configuration details to allow us to successfully connect to our hosts, we can try out our very first command.<\/span><\/p>\n

Ping <\/span>all of<\/span> the servers you configured by typing:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ansible -m ping all<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

Ansible will return output like this:<\/span><\/p>\n

Output<\/span><\/p>\n

host1 | SUCCESS => {<\/span><\/p>\n

“changed”: false,<\/span><\/p>\n

“ping”: “pong”<\/span><\/p>\n

}<\/span><\/p>\n

.<\/span><\/span><\/p>\n

host3 | SUCCESS => {<\/span><\/p>\n

“changed”: false,<\/span><\/p>\n

“ping”: “pong”<\/span><\/p>\n

}<\/span><\/p>\n

.<\/span><\/span><\/p>\n

host2 | SUCCESS => {<\/span><\/p>\n

“changed”: false,<\/span><\/p>\n

“ping”: “pong”<\/span><\/p>\n

}<\/span><\/p>\n

This is a basic test to make sure that Ansible has a connection to <\/span>all of<\/span> its <\/span>hosts.<\/span><\/p>\n

The\u00a0<\/span>-m ping<\/span>\u00a0portion of the command is an instruction to Ansible to use the “ping” module. These are basically <\/span>commands<\/span> that you can run on your remote hosts. The ping module operates in many ways like the normal ping utility in Linux, but instead it<\/span> checks for Ansible connectivity.<\/span><\/p>\n

The\u00a0<\/span>all<\/span>\u00a0portion means “all hosts.” You could just as easily specify a group:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ansible -m ping servers<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

You can also specify an individual host:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ansible -m ping host1<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

You can specify multiple hosts by separating them <\/span>with colons:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ansible -m ping host<\/span>1:host<\/span>2<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

The\u00a0<\/span>shell<\/span>\u00a0module lets us send a terminal command to the remote host and retrieve the results. For instance, to find out the memory usage on our host1 machine, we could use:<\/span><\/p>\n

\n
\n
\u2022<\/span>\u00a0<\/span>ansible -m shell -a ‘free -m’ host1<\/span><\/div>\n<\/div>\n
\n
\u2022<\/span>\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n

As <\/span>you can see, you pass arguments into a script by using the\u00a0<\/span>-a<\/span>\u00a0switch. <\/span>Here’s<\/span> what the output might look like:<\/span><\/p>\n

Output<\/span><\/p>\n

host1 | SUCCESS | <\/span>rc<\/span>=0 >><\/span><\/p>\n

total used free shared buffers cached<\/span><\/p>\n

Mem: 3954 227 <\/span> 3726 0 14 93<\/span><\/p>\n

-\/+ buffers\/cache: 119 3834<\/span><\/p>\n

Swap: 0 0 0<\/span><\/p>\n

.<\/span><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Prerequisites To follow this tutorial, you will need: Step 1 \u2014 Installing Ansible To begin exploring Ansible as a means of managing our various servers, we need to install the Ansible software on at least one machine. To get Ansible for CentOS 7, first ensure that the CentOS 7 EPEL repository is installed: \u2022\u00a0sudo yum install epel-release \u2022\u00a0 Once theRead More …<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[51,58],"tags":[],"class_list":["post-724","post","type-post","status-publish","format-standard","hentry","category-ansible","category-centos"],"_links":{"self":[{"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/posts\/724","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/comments?post=724"}],"version-history":[{"count":7,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/posts\/724\/revisions"}],"predecessor-version":[{"id":1057,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/posts\/724\/revisions\/1057"}],"wp:attachment":[{"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/media?parent=724"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/categories?post=724"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nicktailor.com\/tech-blog\/wp-json\/wp\/v2\/tags?post=724"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}