Tag: ansible-playbook

Ansible – gather facts (playbook)

admin

Ansible provides valuable information about the nodes (server/system) through ansible gather facts.

Ansible ad-hoc command uses a setup module to get the facts, refer to our earlier post for more detail on the Ansible Ad-Hoc setup module.

Ansible playbook on the other hand by default collects the fact information. This fact information is stored in a variable called ansible_facts.

Example

---
 - name: Ansible Playbook - Get facts 
   hosts: localhost

   tasks: 
   - name: Ansible-playbook will gather facts by default. The facts are stored in ansible_facts variable.
     debug:
      msg:
      - "{{ansible_facts }}"

The above playbook will print all ansible fact information like the setup command, but we do not need all this information, or we need a few details. To fetch the required details we must know the keys.

We can get the keys using two methods,

Run the ansible ad-hoc command

ansible localhost -m setup | grep ansible
ansible gather facts – ad-hoc command

As we can see from the above output, all variables are listed with the prefix ansible. We can directly use these variables in our playbook to fetch the specific fact information.

The second method is to run the setup command and then add an ansible prefix to the dictionary root keys.

ansible gather facts – default facts

As we can see from the ansible fact output we can select the key name and just add the prefix ansible to create the variable.

Example

---
 - name: Ansible Playbook - Get facts 
   hosts: localhost

   tasks: 
   - name: Ansible-playbook will gather facts by default. The facts are stored in ansible_facts variable.
     debug:
      msg:
      - "{{ansible_facts }}"

   - name: get indiviual tasks from the facts. 
     debug:
      msg:
      - "{{ansible_distribution}}"
      - "{{ansible_system}}"
      - "{{ansible_lsb['description']}}"
ansible gather facts – custom output

Ansible – Variables through command line argument

admin

sometimes we do not want to declare a variable value hard-coded in the playbook file instead, we want it to be passed dynamically during execution.

Ansible does support passing variables dynamically through command arguments.

We have covered Ansible Variables, and the Ansible Data Types in our earlier post,

To pass variables through the command line argument, use flag –extra-var or -e.

Syntax

ansible-playbook <playbook_name> -e <var>=<varvalue>

or

ansible-playbook <playbook_name> --extra-var <var>=<varvalue>

We can pass single as well as multiple variables through command arguments.

# Pass variable through the command line argument
---
 - name: Playbook - Variable through command line argument
   hosts: localhost

   tasks:
   - name: Pass single variable through cmd argument
     debug:
      msg:
      - "The Operating System runnings is {{os}}"
      - "The Operating System is {{os}} and base_version : {{version}}"

Example: Single command argument

ansible-playbook ansible_vars_cmd_arg.yml -e os=linux

or

ansible-playbook ansible_vars_cmd_arg.yml -e "{'os' : 'ubuntu'}"

or

ansible-playbook ansible_vars_cmd_arg.yml --extra-var "{'os' : 'ubuntu'}"
ansible single variable command argument

Example: Multiple variable command argument

ansible-playbook ansible_vars_cmd_arg.yml -e "os=Ubuntu version=20.04"

or

ansible-playbook ansible_vars_cmd_arg.yml -e "{'os':'ubuntu', 'version':'20.04'}"

or

ansible-playbook ansible_vars_cmd_arg.yml --extra-var "{'os':'ubuntu', 'version':'20.04'}"
ansible multiple variable command argument

We can also pass complex data types List and Maps, through command arguments

Example: List variable command argument

ansible-playbook ansible_vars_cmd_arg.yml -e "{'list_var':['Ubuntu','Windows','Mac']}"
ansible list variable command argument

Example: Map variable command argument

ansible-playbook ansible_vars_cmd_arg.yml -e "{'list_var':{'os':'Ubuntu','version':'20.04'}}"
ansible map variable command argument

We can pass variable files through command arguments. More details on declaring file variables.

Example: File variable command argument

# Pass variable through the command line argument
---
 - name: Playbook - Variable through command line argument
   hosts: localhost

   tasks:
   - name: Pass variable file through command argument
     debug:
      msg:
      # map_os is a variable defined in file variable.yml
      - "Passing variable through variable file {{map_os}}"

Syntax

ansible-playbook <playbook-file> -e "@<variable_file.yml>"
or
ansible-playbook <playbook-file> --extra-var "@<variable_file.yml>"

Example

ansible-playbook ansible_vars_cmd_arg.yml -e "@variable.yml"
ansible file variable command argument

Summary: Ansible does provide us with various methods to pass variables dynamically. Dynamic variable passing through command argument allows reusing the code.

For a real-time example, let us consider that we want to install/un-install multiple packages on our system/servers. In normal circumstances, we would go writing tasks for each package.

To avoid writing tasks for each package, we can pass the package name as variables dynamically and the same piece of configuration code can be used for installing multiple packages by just passing the package name through the command arguments.

More details on Ansible Variables can be found on Ansible Official Documents

Ansible – Variable file

admin

Ansible does support passing the variables through files. The variable files can be created in JSON and YAML format.

We have covered Ansible Variables, and the Ansible Data Types in our earlier post,

Example of Ansible YAML variable file,

# variables in yaml
---
 number: 10
 str_ex: "john"
 lists_ex:
 - "new york"
 - "london"
 - "sydney"
 - "mumbai"
 map_ex: 
 - "name": "john"
 - "address": "Chicago"
 - "country": "US"
 map_ex_2: {"os": "windows", "patch": "2.5", "version": 10}

Example of Ansible JSON variable file,

{
    "number": 6,
    "name": "Mike",
    "list": [1, "apple", 5, "fruit"],
    "map": {"os": "Ubuntu", "patch": "2.5", "version": 18.10}
}

Ansible playbook supports both single variable files as well multiple variable files.

Ansible playbook with single variable file,

---
# ansible play for variable through file
 - name: Ansible supports variables from json and yaml files
   hosts: localhost
   vars_files: variable.yml
   
   tasks:
   - name: Lets print vales from single variable file
     debug:
      msg:
      - "Printing value form variable file {{map_ex_2}}"
      - "printing the secong map example {{map_ex}}"
ansible-playbook variable single file

Ansible playbook with multiple variable files,

 # Ansible play to read variable through multiple files
 - name: ansible playbook from multiple files
   hosts: localhost
   vars_files:
   - variable.yml
   - variable.json

   tasks:
   - name: Lets print the variables from two different files
     debug:
      msg:
      - "Reading variable through json {{map}}"
      - "Reading variable through YAML {{map_ex_2}}"
ansible-playbook variable multiple files

Summary:

Ansible variable files help in organizing variables in a single YAML/JSON file. That allows ease in the modification of the variables.

We don’t need to define the variables in each playbook. Instead, the variables can be defined in a file and called in all playbooks as per the requirements.

More details on Ansible Variables can be found on Ansible Official Documents

Ansible – register variable

admin

Often we require to store the result of our command outputs in any variables, so we can use them further as inputs or just display them on our output screen.

Ansible does offer us to store or print the output results, this can be done using the Ansible register variable.

We have covered Ansible Variables, and the Ansible Data Types in our earlier post,

Syntax:

---
 - name: Lets learn Ansible registry
   hosts: localhost

   tasks:
   - name: lets get the bash version
     shell: "bash --version"
     register: bash_version

   - name: lets print the raw output  
     debug:
      msg:
      - "The shell module raw output "
      - "{{bash_version}}"

In the above ansible playbook, we are running the command bash –version. Ansible will run the command but will not display the output.

The register will store the output value of the bash –version command and we can further display the output using the debug module.

Ansible registry

Now let’s play around with the output and get the specific output we want, in our case we need the bash version from the above dictionary/map.

We have covered the Ansible Map data type,

   - name: lets print specific key from output value
     debug:
      msg: # Print array/dictonary/map values 
      - "We can print specific key in three different ways"
      - "Method 1 : Output stdout key from raw output -  " 
      - "{{bash_version.stdout}}"
      - "Method 2 : Output stdout key from raw output -  "
      - "{{bash_version['stdout']}}"
      - "Method 3 : Output stdout key from raw output -  "
      - "{{bash_version.get('stdout')}}"

In our case, the output is in Map/Dictionary format, use the key name to fetch specific values from the Map.

ansible output

Now, let’s split the string using Ansible Split function, as we can see in the below code snippet, we can go on extracting the pattern from the string as per our requirements.

- name: lets split string in the output value 
     debug:
      msg:
      - "Lets Split the output value string - "
      - "{{bash_version.stdout.split('\n')}}"
      - "lets get the first string value - "
      - "{{bash_version.stdout.split('\n')[0]}}"
      - "Now, lets get further stplit it with space - "
      - "{{bash_version.stdout.split('\n')[0].split()}}"
      - "Lets print the version - "
      - "{{bash_version.stdout.split('\n')[0].split()[3]}}"
ansible split string

You can find the full ansible playbook code below,

---
 - name: Lets learn Ansible registry
   hosts: localhost

   tasks:
   - name: lets get the bash version
     shell: "bash --version"
     register: bash_version

   - name: lets print the raw output  
     debug:
      msg:
      - "The shell module raw output "
      - "{{bash_version}}"

   - name: lets print specific key from output value
     debug:
      msg: # Print array/dictonary/map values 
      - "We can print specific key in three different ways"
      - "Method 1 : Output stdout key from raw output -  " 
      - "{{bash_version.stdout}}"
      - "Method 2 : Output stdout key from raw output -  "
      - "{{bash_version['stdout']}}"
      - "Method 3 : Output stdout key from raw output -  "
      - "{{bash_version.get('stdout')}}"

   - name: lets split string in the output value 
     debug:
      msg:
      - "Lets Split the output value string - "
      - "{{bash_version.stdout.split('\n')}}"
      - "lets get the first string value - "
      - "{{bash_version.stdout.split('\n')[0]}}"
      - "Now, lets get further stplit it with space - "
      - "{{bash_version.stdout.split('\n')[0].split()}}"
      - "Lets print the version - "
      - "{{bash_version.stdout.split('\n')[0].split()[3]}}"

Summary

  • Ansible registers can be used to output the module into the variables.
  • These variables can be used further to print the output and used as input variables in the playbook.

Ansible – Data Structure / Collection data type

admin

Ansible support complex data type like data structure or collection types like List, Map, etc.

We have covered Ansible Variables, and the Ansible Data Types in our earlier post,

Ansible Data Structure or Collection types supports,

  • Lists, are a collection of items and are generally represented using the [] brackets. The items in the list are indexed and can be accessed using index values starting from zero.
  • We can define a list in two ways, as shown below.
vars:
    var_list: ['db_server', 'web_server', 'app_server']
    var_list_2:
    - 'db'
    - 'web'
    - 'app'
  • A Map is similar to the python dictionary. In Map, you can have key, and value pairs.
  • We can define Map in two ways as shown below.
vars:
    var_dict: {'db_server':'mysql', 'web_server':'apache', 'app_server':'php'}
    var_dict_2:
     'db': 'mysql'
     'web': 'apache'
     'app': 'php'

Example code of List and Map,

---
 # Ansible Data Structure
 - name: Playbook - Ansible Data Structure 
   hosts: localhost
   vars:
    # Ansible List
    var_list: ['db_server', 'web_server', 'app_server']
    var_list_2:
    - 'db'
    - 'web'
    - 'app'
    # Ansible Map
    var_dict: {'db_server':'mysql', 'web_server':'apache', 'app_server':'php'}
    var_dict_2:
     'db': 'mysql'
     'web': 'apache'
     'app': 'php'

   tasks:
   - name: Lets print the list
     debug: var=var_list
   
   - name: Lets print the dict
     debug: var=var_dict

   - name: lets print the second list
     debug: var=var_list_2

   - name: lets print the second dict
     debug: var=var_dict_2

   - name: Lets print specific list value
     debug:
      msg:
       - "The second value of list is {{var_list[1]}}"
       - "The second value of the dict is {{var_dict_2['web']}}"
       - Another method of calling value from dict {{var_dict.get('app_server')}}
       - lets get all the dict keys {{var_dict.keys()}}
       - lets get all the dict values {{var_dict.values()}}

The below screencap shows the output of the list and map using different methods as defined in the above code.

Ansible – Data Structure

Ansible – variable data type

admin

Ansible variables support various data types, similar to many programming languages.

We have covered the Ansible variables in our earlier post, Ansible Variables

Ansible does offer us a way to check the type of variables used in our playbooks. To check the variables data types in your playbook, use the “type_debug” keyword.

Example:

- name: Playbook - to get the data types
   hosts: localhost
   vars: 
    y: 15
    server_name: "db_server"
    boolean_value: false
    float_value: 10.10

   tasks:
   - name: Lets get the data type
     debug:
      msg:
       - "Variable : {{y}}, is of type {{y | type_debug}}"
       - "Variable : {{server_name}}, is of type {{server_name | type_debug}}"
       - "Variable : {{boolean_value}}, is of type {{boolean_value | type_debug}}"
       - "Variable : {{float_value}}, is of type {{float_value | type_debug}}"

As you can see in the above code, we need to pass pipe operator | and then type_debug.

ansible variable data type

Ansible – Ansible playbook dry run

admin

The dry run is the best way to analyze the possible outcome of the configuration management code. Ansible playbook dry run command allows us to check the potential effects on our infrastructure/applications upon execution of the Ansible playbook.

Syntax

ansible-playbook pkg_install.yml --check
Ansible playbook dry run –check command

The ansible-playbook –check command will only provide us the information on changes the code will perform without actually executing the changes.

Ansible – Command to check playbook syntax

admin

Ansible playbooks are one of the best available tools for system/server configuration management, but often we get YAML syntax errors that keep us away from writing the playbooks.

Ansible does provide us with a command to validate the syntax of our playbook for any errors prior to running the Ansible playbook.

Syntax

> ansible-playbook pkg_install.yml --syntax-check

Ansible syntax-check throwing error for a space error in the playbook file.

Ansible-playbook syntax-check error

Ansible syntax-check command output for syntactically correct playbook.

ansible-playbook syntax-check no error