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Ansible-part7: set facts, set variable

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what is set_fact

Set fact is a module which allows setting new variables. These variables are set on a host-by-host base just like facts discovered by the setup module.

In ansible, there are some default info of hosts in hostvars variable, such as “ansible_check_mode”, “group_names” etc, and also the “ansible_facts”, which is not default show up, only when gather_facts is set to “yes”, it will show the details of ansible_fact. Except these two kinds of info, I can also use set_fact module to create my own info pair.

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- name: set fact
  hosts: all
  gather_facts: no

  tasks:
    - name: gather facts
      debug:
        var: hostvars[ansible_host]    #ansible_host is variable name, which means cube4200 and ansible-node1 in this case

Let’s look at he output of this playbook,

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anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$ ansible-playbook site.yml 

PLAY [set fact] ************************************************************************

TASK [gather facts] ********************************************************************
ok: [cube4200] => {
    "hostvars[ansible_host]": {
        "ansible_check_mode": false, 
        "ansible_connection": "ssh", 
        "ansible_diff_mode": false, 
        "ansible_facts": {}, 
        "ansible_forks": 5, 
        "ansible_inventory_sources": [
            "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts"
        ], 
        "ansible_playbook_python": "/usr/bin/python2", 
        "ansible_run_tags": [
            "all"
        ], 
        "ansible_skip_tags": [], 
        "ansible_user": "anna", 
        "ansible_verbosity": 0, 
        "ansible_version": {
            "full": "2.9.9", 
            "major": 2, 
            "minor": 9, 
            "revision": 9, 
            "string": "2.9.9"
        }, 
        "group_names": [
            "web2"
        ], 
        "groups": {
            "all": [
                "cube4200", 
                "ansible-node1"
            ], 
            "ungrouped": [], 
            "web1": [
                "ansible-node1"
            ], 
            "web2": [
                "cube4200"
            ]
        }, 
        "inventory_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "inventory_file": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts", 
        "inventory_hostname": "cube4200", 
        "inventory_hostname_short": "cube4200", 
        "omit": "__omit_place_holder__a53469922527cea947bde7fea01f0f911fe92d8c", 
        "playbook_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module"
    }
}
ok: [ansible-node1] => {
    "hostvars[ansible_host]": {
        "ansible_check_mode": false, 
        "ansible_connection": "ssh", 
        "ansible_diff_mode": false, 
        "ansible_facts": {}, 
        "ansible_forks": 5, 
        "ansible_inventory_sources": [
            "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts"
        ], 
        "ansible_playbook_python": "/usr/bin/python2", 
        "ansible_run_tags": [
            "all"
        ], 
        "ansible_skip_tags": [], 
        "ansible_user": "pi", 
        "ansible_verbosity": 0, 
        "ansible_version": {
            "full": "2.9.9", 
            "major": 2, 
            "minor": 9, 
            "revision": 9, 
            "string": "2.9.9"
        }, 
        "group_names": [
            "web1"
        ], 
        "groups": {
            "all": [
                "cube4200", 
                "ansible-node1"
            ], 
            "ungrouped": [], 
            "web1": [
                "ansible-node1"
            ], 
            "web2": [
                "cube4200"
            ]
        }, 
        "inventory_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "inventory_file": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts", 
        "inventory_hostname": "ansible-node1", 
        "inventory_hostname_short": "ansible-node1", 
        "omit": "__omit_place_holder__a53469922527cea947bde7fea01f0f911fe92d8c", 
        "playbook_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module"
    }
}

PLAY RECAP *****************************************************************************
ansible-node1              : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
cube4200                   : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

eventhought gather_facts is “no”, ansible still show some basic info of every hosts.
If gather_facts is “yes”, except the default info, ansible will show ansible-facts info which included a lots of system info of every hosts.

If I add set_fact module, and create a variable named test_set_fact, it will show in the output of hostvars, notice line 56 and line 105

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- name: set fact
  hosts: all
  gather_facts: no

  tasks:
    - name: test facts
      set_fact:
        test_set_fact: "variable from set fact"
    - debug:
        var: hostvars[ansible_host]    #ansible_host is variable name, which means cube4200 and ansible-node1 in this case

Let’s look at the output

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anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$ ansible-playbook site.yml 

PLAY [set fact] ***************************************************************************************************************************************************************************************************************************************

TASK [test facts] *************************************************************************************************************************************************************************************************************************************
ok: [cube4200]
ok: [ansible-node1]

TASK [debug] ******************************************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "hostvars[ansible_host]": {
        "ansible_check_mode": false, 
        "ansible_connection": "ssh", 
        "ansible_diff_mode": false, 
        "ansible_facts": {}, 
        "ansible_forks": 5, 
        "ansible_inventory_sources": [
            "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts"
        ], 
        "ansible_playbook_python": "/usr/bin/python2", 
        "ansible_run_tags": [
            "all"
        ], 
        "ansible_skip_tags": [], 
        "ansible_user": "anna", 
        "ansible_verbosity": 0, 
        "ansible_version": {
            "full": "2.9.9", 
            "major": 2, 
            "minor": 9, 
            "revision": 9, 
            "string": "2.9.9"
        }, 
        "group_names": [
            "web2"
        ], 
        "groups": {
            "all": [
                "cube4200", 
                "ansible-node1"
            ], 
            "ungrouped": [], 
            "web1": [
                "ansible-node1"
            ], 
            "web2": [
                "cube4200"
            ]
        }, 
        "inventory_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "inventory_file": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts", 
        "inventory_hostname": "cube4200", 
        "inventory_hostname_short": "cube4200", 
        "omit": "__omit_place_holder__d4f2446f1f2a785d53a7d7fe3b7b731b4fa322b3", 
        "playbook_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "test_set_fact": "variable from set fact"
    }
}
ok: [ansible-node1] => {
    "hostvars[ansible_host]": {
        "ansible_check_mode": false, 
        "ansible_connection": "ssh", 
        "ansible_diff_mode": false, 
        "ansible_facts": {}, 
        "ansible_forks": 5, 
        "ansible_inventory_sources": [
            "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts"
        ], 
        "ansible_playbook_python": "/usr/bin/python2", 
        "ansible_run_tags": [
            "all"
        ], 
        "ansible_skip_tags": [], 
        "ansible_user": "pi", 
        "ansible_verbosity": 0, 
        "ansible_version": {
            "full": "2.9.9", 
            "major": 2, 
            "minor": 9, 
            "revision": 9, 
            "string": "2.9.9"
        }, 
        "group_names": [
            "web1"
        ], 
        "groups": {
            "all": [
                "cube4200", 
                "ansible-node1"
            ], 
            "ungrouped": [], 
            "web1": [
                "ansible-node1"
            ], 
            "web2": [
                "cube4200"
            ]
        }, 
        "inventory_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "inventory_file": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module/hosts", 
        "inventory_hostname": "ansible-node1", 
        "inventory_hostname_short": "ansible-node1", 
        "omit": "__omit_place_holder__d4f2446f1f2a785d53a7d7fe3b7b731b4fa322b3", 
        "playbook_dir": "/home/anna/Desktop/ansible-code/inventory/modules/set-fact module", 
        "test_set_fact": "variable from set fact"
    }
}

PLAY RECAP ********************************************************************************************************************************************************************************************************************************************
ansible-node1              : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
cube4200                   : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

At last line of every hosts,I can see the "test_set_fact": "variable from set fact", which is the variable and value I set in the playbook before.

How to use set_fact varible

I can call this variable directly in playbook

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tasks:
    - name: test facts
      set_fact:
        test_set_fact: "variable from set fact"
    - debug:
        var: test_set_fact

debug module will show only test_set_fact variable

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anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$ ansible-playbook site.yml 

PLAY [set fact] ***************************************************************************************************************************************************************************************************************************************

TASK [test facts] *************************************************************************************************************************************************************************************************************************************
ok: [cube4200]
ok: [ansible-node1]

TASK [debug] ******************************************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "test_set_fact": "variable from set fact"
}
ok: [ansible-node1] => {
    "test_set_fact": "variable from set fact"
}

another example
I am going to get the every hosts’s hostname info.

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tasks:
    - name: test facts
      set_fact:
        test_set_fact: "variable from set fact"
    - command: cat /etc/hosts
      register: hosts_result
    - debug:
        var: hosts_result

I put all the output of command cat /etc/hosts into variable named hosts_result, then it will show like this

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anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$ ansible-playbook site.yml 

PLAY [set fact] ***************************************************************************************************************************************************************************************************************************************

TASK [test facts] *************************************************************************************************************************************************************************************************************************************
ok: [cube4200]
ok: [ansible-node1]

TASK [command] ****************************************************************************************************************************************************************************************************************************************
changed: [ansible-node1]
changed: [cube4200]

TASK [debug] ******************************************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "hosts_result": {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python"
        }, 
        "changed": true, 
        "cmd": [
            "cat", 
            "/etc/hosts"
        ], 
        "delta": "0:00:00.011381", 
        "end": "2020-06-13 14:38:12.510727", 
        "failed": false, 
        "rc": 0, 
        "start": "2020-06-13 14:38:12.499346", 
        "stderr": "", 
        "stderr_lines": [], 
        "stdout_lines": [
            "127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4", 
            "::1         localhost localhost.localdomain localhost6 localhost6.localdomain6"
        ]
    }
}
ok: [ansible-node1] => {
    "hosts_result": {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python"
        }, 
        "changed": true, 
        "cmd": [
            "cat", 
            "/etc/hosts"
        ], 
        "delta": "0:00:00.014459", 
        "end": "2020-06-13 21:38:08.778027", 
        "failed": false, 
        "rc": 0, 
        "start": "2020-06-13 21:38:08.763568", 
        "stderr": "", 
        "stderr_lines": [], 
        "stdout_lines": [
            "127.0.0.1\tlocalhost", 
            "::1\t\tlocalhost ip6-localhost ip6-loopback", 
            "ff02::1\t\tip6-allnodes", 
            "ff02::2\t\tip6-allrouters", 
            "", 
            "127.0.1.1\ttreehouses"
        ], 
        "warnings": [
            "Platform linux on host ansible-node1 is using the discovered Python interpreter at /usr/bin/python, but future installation of another Python interpreter could change this. See https://docs.ansible.com/ansible/2.9/reference_appendices/interpreter_discovery.html for more information."
        ]
    }
}

PLAY RECAP ********************************************************************************************************************************************************************************************************************************************
ansible-node1              : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
cube4200                   : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

but I only want the “stdout_lines” info, so I am going to set “stdout_lines” to a variable named host_ip, and use set_fact module to do this, modified the playbook like this:

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tasks:
    - command: cat /etc/hosts
      register: hosts_result
    - set_fact:
       host_ip: "{{hosts_result['stdout_lines']}}"
    - debug:
        var: host_ip

So the output will be like this

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anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$ ansible-playbook site.yml 

PLAY [set fact] ************************************************************************

TASK [command] *************************************************************************
changed: [ansible-node1]
changed: [cube4200]

TASK [set_fact] ************************************************************************
ok: [cube4200]
ok: [ansible-node1]

TASK [debug] ***************************************************************************
ok: [cube4200] => {
    "host_ip": [
        "127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4", 
        "::1         localhost localhost.localdomain localhost6 localhost6.localdomain6"
    ]
}
ok: [ansible-node1] => {
    "host_ip": [
        "127.0.0.1\tlocalhost", 
        "::1\t\tlocalhost ip6-localhost ip6-loopback", 
        "ff02::1\t\tip6-allnodes", 
        "ff02::2\t\tip6-allrouters", 
        "", 
        "127.0.1.1\ttreehouses"
    ]
}

PLAY RECAP *****************************************************************************
ansible-node1              : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
cube4200                   : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

anna@ansible-controller:~/Desktop/ansible-code/inventory/modules/set-fact module$

It will show only the host ip which I want.