day44.md

On the forty forth day, I learned the following things about Ansible.

There are three ways to push the code from ansible server to the node(s).

1. Ad-hoc commands
2. Modules
3. Playbooks

1. Ad-hoc commands

• Ad-hoc means temporary. It will do the things for a short period of time.

• It can run individually to perform quick funtions like creating the files, running or stopping the machines, etc.

• Ad-hoc commands are the linux commands that will be used for temporary purpose.

• The linux commands have no idempotency. It means that it will do one task repeatedly multiple times. It's the drawback of ad-hoc.

• These ad-hoc commands are not used for configuration management and deployment because the commands are of one time usage.

• The ansible ad-hoc commands uses the /usr/bin/ansible that contains the commands and this command line tool is used to automate a single task.

Steps to use ad-hoc commands

• Start the instances first and then go to the directory where the ansible key is present and use it in the machine by writing ssh -i <file-name.pem> ec2-user@<public-ip-address> command of all three instances.

• Go to ansible server by typing su - ansible.

• ansible <groupname> -a "ls" will execute the ls command in a particular group. -a is an argument that will tell that whatever I am writing in the inverted command should be executed.

• ansible <groupnme>[0] -a "touch filename" will create a file in node1 in a particular group.

• ansible all -a "touch filename" will create a file in all the nodes and in all the groups.

• ansible <groupname> -a "ls -al" will give a long list of hidden files in a particular group.

• ansible <groupname> -a "sudo yum install httpd -y" will install the httpd package in all the nodes in a particular group.

• ansible <groupname> -ba "yum install httpd -y" will install the httpd package in all the nodes in a particular group. Here the sudo is not used. Instead the b(become) is used to perform the sudo functionality.

• ansible <groupname> -ba "yum remove httpd -y" will remove the httpd package in all the nodes of a particular group.

• To check a package, write which httpd. It will show you nothing.

2. Ansible Modules

• Module is a single command or single work that will be executed one at a time.

• Ansible ships with a number of modules(called module library) that can be executed on remote hosts or through playbooks.

• It is present by default in the package.

• Your library of modules can reside on any machine and there are no servers, daemons or database required.

• Where the ansible modules are stored?

  • The default location for the inventory file is /etc/ansible/hosts.

Steps to use modules

• ansible <groupname> -b -m yum -a "pkg=httpd state=present" will install the httpd package in all the nodes of a particular group. The m sign is for module. After that, the a is used to insert the argument but this time there is no linux commands. Instead there is a module command. The next step is the pkg=httpd that will show the package and the state=present will install the package. You can replace present with install also but the present is the standard.

  • To install = present
  • To update = latest
  • To uninstall = absent

• To check a package, write which httpd in both the nodes. It will show the httpd package.

• ansible <groupname> -b -m yum -a "pkg=httpd state=latest" will update the httpd package in all the nodes of a particular group. The state=latest will update the package.

• ansible <groupname> -b -m yum -a "pkg=httpd state=absent" will remove the httpd package in all the nodes of a particular group. The state=absent will remove the package.

• To check a package, write which httpd in both the nodes. It will show you nothing.

• ansible <groupname> -b -m yum -a "pkg=httpd state=present" will install the service in all the nodes and then run the service.

• To check a package, write which httpd in both the nodes. It will show the httpd package.

• To check the status of the service in the nodes, type sudo service httpd status. It will show you the inactive message.

• Type ansible <groupname> -b -m service -a "name=httpd state=started" in the ansible server and it will start the httpd service in all the nodes of a particular group. state=started will start the service.

• To check the status of the service in the nodes, type sudo service httpd status again. It will show you the active message.

• ansible <groupname> -b -m user -a "name=<name>" will create a user in all the nodes of a particular group.

• To check it, type cat /etc/passwd in the nodes terminal and they will show you the newly created user at the end.

• First create a file in the ansible server to copy it.

• ansible <groupname> -b -m copy -a "src=<filename> dest=/tmp" will copy a file from the ansible server and paste it into /tmp directory of all the nodes in a particular group.

• If you want to copy a file into a particular node then type ansible <groupname>[0] -b -m copy -a "src=<filename> dest=/tmp".

• To check the directory, type ls /tmp/ in a particular node.

• ansible <groupname> -b -m user -a "name=<name> state=absent" will remove a user in all the nodes of a particular group.

How the ansible server will know that a package is already present?

• It is possible with the help of idempotency. It means that the ansible server contains the setup module that will send a request to the nodes and that setup module will check a package whether it is present or not. If it is present then it will not overwrite it. If it is present then it will write it in those nodes.

• The setup command will know whether a package is already present or not.

• Run ansible <groupname> -m setup in a server and it will show you all the information of the nodes in a particular group.

• ansible <groupname> -m setup -a "filter=*ipv4*" will give you the ip-address of all the nodes in a particular group.

Explaining it in a video

Here you can get an explanation in a video. 44/60 Day of DevOps Challenge