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Ansible-part12: block rescue and always

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Blocks

Blocks allow for logical grouping of tasks and in play error handling.

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- name: test blocks resuce and always
  hosts: web2
  tasks:
    - name: first command
      debug: 
        msg: "first message success"
    - name: second command
      command: /bin/false
    - name: third command
      debug:
        msg: "this is third command"

There are three tasks in this playbook, but the second one is a wrong command, which will failed to be executed.

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anna@ansible-controller:~/Desktop/ansible-code/inventory/block-resuce-always$ ansible-playbook -i hosts site.yml 

PLAY [test blocks resuce and always] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ********************************************************************************************************************************************************************************************************************************
ok: [cube4200]

TASK [first command] **********************************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "first message sucess"
}

TASK [second command] *********************************************************************************************************************************************************************************************************************************
fatal: [cube4200]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.011635", "end": "2020-06-21 21:31:18.222247", "msg": "non-zero return code", "rc": 1, "start": "2020-06-21 21:31:18.210612", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}

PLAY RECAP ********************************************************************************************************************************************************************************************************************************************
cube4200                   : ok=2    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0

Since the second faild, so the third one will be skipped. I don’t want this happen, So I use block to solove this.

Blocks error handling

Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages. Blocks only deal with ‘failed’ status of a task. A bad task definition or an unreachable host are not ‘rescuable’ errors.

three key words: block rescure always are similar as try exception and final in python.
block section: will execute normally
rescue section: will execute only when block section has error
always section: will run no matter what the task status is.

I add block into playbook

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- name: test blocks recue and always
  hosts: web2
  tasks:
    - block:
      - name: test block, this is first command
        debug: 
          msg: "first message success"
      - name: second command
        command: /bin/false
      rescue:
      - name: third command, this is excuted only when block failed, otherwise will be skipped
        debug:
          msg: "some command in block failed, so this message be excuted"

after running

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anna@ansible-controller:~/Desktop/ansible-code/inventory/block-resuce-always$ ansible-playbook -i hosts site.yml 

PLAY [test blocks resuce and always] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ********************************************************************************************************************************************************************************************************************************
ok: [cube4200]

TASK [test block, this is first command] **************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "first message success"
}

TASK [second command] *********************************************************************************************************************************************************************************************************************************
fatal: [cube4200]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.010445", "end": "2020-06-21 21:42:37.100618", "msg": "non-zero return code", "rc": 1, "start": "2020-06-21 21:42:37.090173", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}

TASK [third command, this is excuted only when block failed, otherwise will be skipped] ***************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "some command in block failed, so this message be excuted"
}

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

eventhough the second command failed, the third command still be excuted since it is in the rescue section.

I am testing another situation

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tasks:
    - block:
      - name: test block, this is first command
        debug: 
          msg: "first message success"
      - name: second command
        command: /bin/date
      rescue:
      - name: third command, this is excuted only when block failed, otherwise will be skipped
        debug:
          msg: "some command in block failed, so this message be excuted"

In this playbook, the second command is correct. what will happed to rescue section?

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anna@ansible-controller:~/Desktop/ansible-code/inventory/block-resuce-always$ ansible-playbook -i hosts site.yml 

PLAY [test blocks resuce and always] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ********************************************************************************************************************************************************************************************************************************
ok: [cube4200]

TASK [test block, this is first command] **************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "first message success"
}

TASK [second command] *********************************************************************************************************************************************************************************************************************************
changed: [cube4200]

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

It shows the rescue section isn’t be excuted any more.

Let’s look at always scenario

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tasks:
    - block:
      - name: test block, this is first command
        debug: 
          msg: "first message success"
      - name: second command
        command: /bin/date
      rescue:
      - name: third command, this is excuted only when block failed, otherwise will be skipped
        debug:
          msg: "some command in block failed, so this message be excuted"
      always:
      - name: test always. whatever this task have to be executed.
        debug:
          msg: "this section definitely be executed!!"

whatever happen, the always section will be executed, but rescue section isn’t excuted since the second command successed.

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anna@ansible-controller:~/Desktop/ansible-code/inventory/block-resuce-always$ ansible-playbook -i hosts site.yml 

PLAY [test blocks resuce and always] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ********************************************************************************************************************************************************************************************************************************
ok: [cube4200]

TASK [test block, this is first command] **************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "first message success"
}

TASK [second command] *********************************************************************************************************************************************************************************************************************************
changed: [cube4200]

TASK [test always. whatever this task have to be executed.] *******************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "this section definitely be executed!!"
}

PLAY RECAP ********************************************************************************************************************************************************************************************************************************************
cube4200                   : ok=4    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

last scenario

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tasks:
    - block:
      - name: test block, this is first command
        debug: 
          msg: "first message success"
      - name: second command
        command: /bin/da
      rescue:
      - name: third command, this is excuted only when block failed, otherwise will be skipped
        debug:
          msg: "some command in block failed, so this message be excuted"
      always:
      - name: test always. whatever this task have to be executed.
        debug:
          msg: "this section definitely be executed!!"

the second command failed, both rescue and always will be excuted.

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anna@ansible-controller:~/Desktop/ansible-code/inventory/block-resuce-always$ ansible-playbook -i hosts site.yml 

PLAY [test blocks resuce and always] ******************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ********************************************************************************************************************************************************************************************************************************
ok: [cube4200]

TASK [test block, this is first command] **************************************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "first message success"
}

TASK [second command] *********************************************************************************************************************************************************************************************************************************
fatal: [cube4200]: FAILED! => {"changed": false, "cmd": "/bin/da", "msg": "[Errno 2] No such file or directory", "rc": 2}

TASK [third command, this is excuted only when block failed, otherwise will be skipped] ***************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "some command in block failed, so this message be excuted"
}

TASK [test always. whatever this task have to be executed.] *******************************************************************************************************************************************************************************************
ok: [cube4200] => {
    "msg": "this section definitely be executed!!"
}

PLAY RECAP ********************************************************************************************************************************************************************************************************************************************
cube4200                   : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=1    ignored=0