Modules Deep Dive
Overview
Ansible have categorized modules based on their functionalities. You can check out more details about the ansible modules in the ansible documentation. These are some of them:
-
SYSTEM MODULES These are performed on the system level, which includes the following:
- User
- Group
- Hostname
- Systemd
- Service
- and more...
-
COMMAND MODULES These are used to execute commands or scripts on hosts. This includes:
- Command
- Expect
- Raw
- Script
- Shell
- and more...
-
FILE MODULES Used for working on files. Examples are:
- Acl
- Archive
- Unarchive
- Copy
- File
- Find
- LininFile
- and more...
-
DATABASE MODULES These is useful in working with databases.
- Mongodb
- Mssql
- Mysql
- Postgresql
- and more...
-
CLOUD MODULES This have a wide selection of modules we can use on the cloud.
- Amazon
- Atomic
- Azure
- Centurylink
- and more...
-
WINDOWS MODULES Useful in a Windows environment.
- win_copy
- win_command
- win_domain
- win_file
- win_iis_website
- and more...
COMMAND MODULE
Executes a command on a remote node. Below is a sample playbook, command.yaml. Ignore the register and debug for now as they will be further discussed in other notes.
-
name: Demo of using command module
hosts: server1
tasks:
-
name: 'Check date'
command: date
register: date
-
name: 'Display test-file.conf contents'
command: cat /etc/test-file.conf
register: display
-
name: 'Switch first to /etc then display test-file.conf contents'
command: chdir=/etc cat test-file.conf
register: change
# This will show the output of the tasks 1-3.
-
name: 'Show variables'
debug:
msg: "{{date}}"
-
name: 'Show variables'
debug:
msg: "{{display}}"
-
name: 'Show variables'
debug:
msg: "{{change}}"
Now try running the command.yaml. You should get a verbose output.
eden@master ansible-lab$ ansible-playbook command.yaml
-i inventory.txt
PLAY [Demo of using command module] ********************************************
TASK [Gathering Facts] *********************************************************
ok: [server1]
TASK [Check date] **************************************************************
changed: [server1]
TASK [Display test-file.conf contents] *****************************************
changed: [server1]
TASK [Switch first to /etc then display test-file.conf
contents] ***************
changed: [server1]
TASK [Show variables] **********************************************************
ok: [server1] => {
"msg": {
"changed": true,
"cmd": [
"date"
],
"delta": "0:00:00.003777",
"end": "2021-01-24 05:00:31.992738",
"failed": false,
"rc": 0,
"start": "2021-01-24 05:00:31.988961",
"stderr": "",
"stderr_lines": [],
"stdout": "Sun Jan 24 05:00:31 UTC 2021",
"stdout_lines": [
"Sun Jan 24 05:00:31 UTC 2021"
]
}
}
TASK [Show variables] **********************************************************
ok: [server1] => {
"msg": {
"changed": true,
"cmd": [
"cat",
"/etc/test-file.conf"
],
"delta": "0:00:00.003765",
"end": "2021-01-24 05:00:32.366377",
"failed": false,
"rc": 0,
"start": "2021-01-24 05:00:32.362612",
"stderr": "",
"stderr_lines": [],
"stdout": "This is a sample file for the Practice 2 in the Ansible lab.",
"stdout_lines": [
"This is a sample file for the Practice 2 in the Ansible lab."
]
}
}
TASK [Show variables] **********************************************************
ok: [server1] => {
"msg": {
"changed": true,
"cmd": [
"cat",
"test-file.conf"
],
"delta": "0:00:00.003579",
"end": "2021-01-24 05:00:32.725967",
"failed": false,
"rc": 0,
"start": "2021-01-24 05:00:32.722388",
"stderr": "",
"stderr_lines": [],
"stdout": "This is a sample file for the Practice 2 in the Ansible lab.",
"stdout_lines": [
"This is a sample file for the Practice 2 in the Ansible lab."
]
}
}
PLAY RECAP *********************************************************************
server1 : ok=7 changed=3 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
Here we have create-folder.yaml which uses a parameter called parameter which checks first if the folder or file already exists before creating them.
-
name: 'Create ansible-test folder in target machine'
hosts: server1
tasks:
-
name: 'Create ansible-test folder on server1'
command: mkdir ./ansible-test creates=./ansible-test
Running create-folder.yaml
eden@master ansible-lab$ ansible-playbook create-folder.yaml -i inventory.txt
PLAY [Create ansible-test folder in target machine] ****************************
TASK [Gathering Facts] *********************************************************
ok: [server1]
TASK [Create ansible-test folder on server1] ***********************************
[WARNING]: Consider using the file module with state=directory rather than
running 'mkdir'. If you need to use command because file is insufficient you
can add 'warn: false' to this command task or set 'command_warnings=False' in
ansible.cfg to get rid of this message.
changed: [server1]
PLAY RECAP *********************************************************************
server1 : ok=2 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
Checking server1, we see that the folder was created.
eden@server1 ~$ pwd
/home/eden
eden@server1 ~$ ll
total 0
drwxrwxr-x. 2 eden eden 6 Jan 24 05:19 ansible-test
SCRIPT
Runs a local script (located on the master or controller machine) on a remote node after transferring it. The way ansible does this, it copies the script onto the remote nodes and runs them there.
A sample playbook which uses the script module:
-
name: Demo for usign script module
hosts: all
tasks:
-
name: Run script on remote server
script: /some/local/script.sh -arg1 -arg2
SERVICES MODULE
Used to manage and maintain services on a system. This includes start, stop, or restarting services. For this, there's two ways to write the statements:
The first method is having the parameters of the services module in one line:
-
name: Start services in order
host: all
tasks:
-
name: Start the DB service
service: name=mysql state=started
The second method is writing the parameters in separate lines.
-
name: Start services in order
host: all
tasks:
-
name: Start the DB service
service:
name: mysql
state: started
Why is the state STARTED and not START? Recall that we are telling Ansible the desired state. Thus we use started to instruct Ansible to ensure thathttpd is started. This also means:
if httpd is not already started ----> start it if httpd is already started, ----> do nothing
As mentioned before, this is the concept of IDEMPOTENCY - an operation is idempotent is the result of performing it once is exactly the same as the result of performing it repeatedly without any intervening actions
LINEINFILE MODULE
Search for a line in a file and replace it or add it if it does nto exist. For example, we're given a task to add servers to the /ansible-test/sample-file.txt file in server1. (Note that you shuold have a ~/ansible-test/sample-file.txt in server1)
- server 10.0.0.125
- server 10.0.0.126
The way to do this is to use the lineinfile module.
Here we have add.yaml
-
name: Add servers to /ansible-test/sample-file.txt on server1
hosts: server1
tasks:
-
name: Add first server to /ansible-test/sample-file.txt
lineinfile:
path: ~/ansible-test/sample-file.txt
line: 'server 10.0.0.125'
-
name: Add second server to /ansible-test/sample-file.txt
lineinfile:
path: ~/ansible-test/sample-file.txt
line: 'server 10.0.0.126'
Running add.yaml
eden@master ansible-lab$ ansible-playbook add.yaml -i inventory.txt
PLAY [Add servers to /ansible-test/sample-file.txt on server1] ******************************************************
TASK [Gathering Facts] **********************************************************************************************
ok: [server1]
TASK [Add first server to /ansible-test/sample-file.txt] ************************************************************
changed: [server1]
TASK [Add second server to /ansible-test/sample-file.txt] ***********************************************************
changed: [server1]
PLAY RECAP **********************************************************************************************************
server1 : ok=3 changed=2 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
Checking on server1, you should see that the two server addresses are added to the destination file.
eden@server1 ansible-test$ pwd
/home/eden/ansible-test
eden@server1 ansible-test$ cat sample-file.txt
server 10.0.0.125
server 10.0.0.126