Ansible playbook的block
环境
- 控制节点：Ubuntu 22.04
- Ansible 2.10.8
- 管理节点：CentOS 8
block
顾名思义，通过block可以把task按逻辑划分到不同的“块”里面，实现“块操作”。此外，block还提供了错误处理功能。
task分组
下面的例子，把3个task放到一个block里面。
创建文件 testBlock1.yml 如下：
---
- name: testBlock1
hosts: all
tasks:
- name: My task 1
block:
- name: Part1
debug:
msg: "Hello Zhang San"
- name: Part2
debug:
msg: "Hello Li Si"
- name: Part3
debug:
msg: "Hello Wang Wu"
when: 2 > 1
运行结果如下：
➜ temp ansible-playbook testBlock1.yml
PLAY [testBlock1] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Zhang San"
}
TASK [Part2] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Li Si"
}
TASK [Part3] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Wang Wu"
}
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=4 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
如果把block的判断条件 when: 2 > 1 改为 when: 2 == 1 ，则运行结果如下：
➜ temp ansible-playbook testBlock1.yml
PLAY [testBlock1] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
skipping: [192.168.1.55]
TASK [Part2] ***************************************************************************************
skipping: [192.168.1.55]
TASK [Part3] ***************************************************************************************
skipping: [192.168.1.55]
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=1 changed=0 unreachable=0 failed=0 skipped=3 rescued=0 ignored=0
可见，由于条件不满足，block里的3个task都没有执行。
错误处理
如果block里的某个task出错了，则后面的task不再运行。
创建文件 testBlock2.yml 如下：
---
- name: testBlock2
hosts: all
tasks:
- name: My task 1
block:
- name: Part1
debug:
msg: "Hello Zhang San"
- name: Part2
command: /bin/false # will trigger an error
- name: Part3
debug:
msg: "Hello Li Si"
运行结果如下：
➜ temp ansible-playbook testBlock2.yml
PLAY [testBlock2] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Zhang San"
}
TASK [Part2] ***************************************************************************************
fatal: [192.168.1.55]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.001904", "end": "2023-10-26 08:50:36.850526", "msg": "non-zero return code", "rc": 1, "start": "2023-10-26 08:50:36.848622", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=2 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0
可见，由于Part2出错，Part3并没有运行。
Ansible的错误处理有两个关键字：
rescue：类似于catchalways：类似于finally
先加上 always 看看效果：
---
- name: testBlock2
hosts: all
tasks:
- name: My task 1
block:
- name: Part1
debug:
msg: "Hello Zhang San"
- name: Part2
command: /bin/false # will trigger an error
- name: Part3
debug:
msg: "Hello Li Si"
always:
- name: Always do this
debug:
msg: "End End End"
➜ temp ansible-playbook testBlock2.yml
PLAY [testBlock2] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Zhang San"
}
TASK [Part2] ***************************************************************************************
fatal: [192.168.1.55]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.002734", "end": "2023-10-26 08:52:19.329781", "msg": "non-zero return code", "rc": 1, "start": "2023-10-26 08:52:19.327047", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}
TASK [Always do this] ******************************************************************************
ok: [192.168.1.55] => {
"msg": "End End End"
}
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=3 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0
可见，Part2出错， always 也会运行（当然，Part3不会运行）。
注意：加上 always ，failed仍然是1。
现在来试一下 rescue ：
---
- name: testBlock2
hosts: all
tasks:
- name: My task 1
block:
- name: Part1
debug:
msg: "Hello Zhang San"
- name: Part2
command: /bin/false # will trigger an error
- name: Part3
debug:
msg: "Hello Li Si"
always:
- name: Always do this
debug:
msg: "End End End"
rescue:
- name: Rescue tasks
debug:
msg: "Something is wrong!"
运行结果如下：
➜ temp ansible-playbook testBlock2.yml
PLAY [testBlock2] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
ok: [192.168.1.55] => {
"msg": "Hello Zhang San"
}
TASK [Part2] ***************************************************************************************
fatal: [192.168.1.55]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.001726", "end": "2023-10-26 09:00:01.785445", "msg": "non-zero return code", "rc": 1, "start": "2023-10-26 09:00:01.783719", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}
TASK [Rescue tasks] ********************************************************************************
ok: [192.168.1.55] => {
"msg": "Something is wrong!"
}
TASK [Always do this] ******************************************************************************
ok: [192.168.1.55] => {
"msg": "End End End"
}
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=4 changed=0 unreachable=0 failed=0 skipped=0 rescued=1 ignored=0
注意，always是在rescue之后运行的（Part3仍然不会运行）。
注：如果task没有出错， rescue 不会被触发。
rescue与handler
我们知道，当task运行成功，状态改变时，可以用 notify 来触发handler。但如果后续的task出错了，则当前task的handler并不会触发。如果有 rescue ，则handler仍然会被触发（在 always 之后）。在 rescue 中可以通过 meta: flush_handlers 来立即触发handler（在 always 之前）。
---
- name: testBlock2
hosts: all
tasks:
- name: My task 1
block:
- name: Part1
debug:
msg: "Hello Zhang San"
changed_when: true
notify: Run me even after an error
- name: Part2
command: /bin/false # will trigger an error
- name: Part3
debug:
msg: "Hello Li Si"
always:
- name: Always do this
debug:
msg: "End End End"
rescue:
- name: Rescue tasks
#debug:
# msg: "Something is wrong!"
meta: flush_handlers
handlers:
- name: Run me even after an error
debug:
msg: 'This handler runs even on error'
运行结果如下：
➜ temp ansible-playbook testBlock2.yml
PLAY [testBlock2] **********************************************************************************
TASK [Gathering Facts] *****************************************************************************
ok: [192.168.1.55]
TASK [Part1] ***************************************************************************************
changed: [192.168.1.55] => {
"msg": "Hello Zhang San"
}
TASK [Part2] ***************************************************************************************
fatal: [192.168.1.55]: FAILED! => {"changed": true, "cmd": ["/bin/false"], "delta": "0:00:00.002172", "end": "2023-10-26 09:11:26.530609", "msg": "non-zero return code", "rc": 1, "start": "2023-10-26 09:11:26.528437", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}
RUNNING HANDLER [Run me even after an error] *******************************************************
ok: [192.168.1.55] => {
"msg": "This handler runs even on error"
}
TASK [Always do this] ******************************************************************************
ok: [192.168.1.55] => {
"msg": "End End End"
}
PLAY RECAP *****************************************************************************************
192.168.1.55 : ok=4 changed=1 unreachable=0 failed=0 skipped=0 rescued=1 ignored=0
本例中，Part1运行成功，且改变了状态，所以触发了handler Run me even after an error 。但由于Part2出错，如果没有 rescue ，则Part1的handler不会触发。加上 rescue 之后，就会触发Part1的handler。本例中加上了 meta: flush_handlers ，所以会立即触发handler。
参考
https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_blocks.html