きっかけ
今回は、時々つまづく Ansible の変数の仕様に関するメモです。
最近、Amazon Linux 1（そろそろ完全に廃止しないといけない……）と Amazon Linux 2 で処理を分岐させたいことがあり、同僚にこういう書き方でできるよと教えてもらいました。
- name: Task for Amazon Linux 2 debug: msg="Task for Amazon Linux 2" when: (ansible_distribution_file_variety == "Amazon" and ansible_distribution_major_version == "2")
以前は ansible_distribution_major_version がいずれも NA になっていたようなのですが、現在は Amazon Linux 2 なら "2" が返されるようです。
ただ、毎回この長い when を書くのは面倒なので、以下のように playbook の冒頭で定義するようにしてみました。
- hosts: hogehoge
vars:
amzn2: (ansible_distribution_file_variety == "Amazon" and ansible_distribution_major_version == "2")
tasks:
- name: Task for Amazon Linux 2
debug: msg="Task for Amazon Linux 2"
when: amzn2
- name: Task NOT for Amazon Linux 2
debug: msg="Task NOT for Amazon Linux 2"
when: not amzn2
しかし、この書き方をすると、以下の DEPRECATION WARNING が出てしまいます。
TASK [Task for Amazon Linux 2] ***************************************************************************************
[DEPRECATION WARNING]: evaluating (ansible_distribution_file_variety == "Amazon" and
ansible_distribution_major_version == "2") as a bare variable, this behaviour will go away and you might need to add
|bool to the expression in the future. Also see CONDITIONAL_BARE_VARS configuration toggle.. This feature will be
removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
ok: [hogehoge] => {
"msg": "Task for Amazon Linux 2"
}
TASK [Task NOT for Amazon Linux 2] ***********************************************************************************
skipping: [hogehoge]
なるほど。じゃあ、面倒ですけど、警告文にあるように |bool を書き足します。
- hosts: hogehoge
vars:
amzn2: (ansible_distribution_file_variety == "Amazon" and ansible_distribution_major_version == "2")
tasks:
- name: Task for Amazon Linux 2
debug: msg="Task for Amazon Linux 2"
when: amzn2|bool
- name: Task NOT for Amazon Linux 2
debug: msg="Task NOT for Amazon Linux 2"
when: not amzn2|bool
すると、DEPRECATION WARNING は出なくなったのですが、実行結果が期待と真逆になってしまいました……なんで？
TASK [Task for Amazon Linux 2] ***************************************************************************************
skipping: [hogehoge]
TASK [Task NOT for Amazon Linux 2] ***********************************************************************************
ok: [hogehoge] => {
"msg": "Task NOT for Amazon Linux 2"
}
結論
文字列比較の結果を代入する際に "{{ }}" で囲むと、文字列ではなく boolean として代入されます。DEPRECATION WARNING にある |bool は不要です。
上の例で言うと、
vars:
amzn2: "{{ ansible_distribution_file_variety == \"Amazon\" and ansible_distribution_major_version == \"2\" }}"
と書くと、以下のように DEPRECATION WARNING が出ず、実行結果も期待通りになりました。
TASK [Task for Amazon Linux 2] ***************************************************************************************
ok: [hogehoge] => {
"msg": "Task for Amazon Linux 2"
}
TASK [Task NOT for Amazon Linux 2] ***********************************************************************************
skipping: [hogehoge]
実験
文字列比較の内容は何でもいいので、("1" == "1") という単純な条件式で実験します。以下の実験は、Ansible 2.9 の最新版（2.9.6）で行いました。
いろいろな方法での代入
まず、代入した値をそのまま debug モジュールで出力してみます。
playbook:
- hosts: localhost
connection: local
vars:
var1: True
var2: False
var3: "True"
var4: "False"
var5: ("1" == "1")
var6: ("1" == "1")|bool
var7: "{{ ('1' == '1') }}"
var8: "{{ ('1' == '1')|bool }}"
tasks:
- name: Print vars
debug: msg="{{ item }}"
with_items:
- "{{ var1 }}"
- "{{ var2 }}"
- "{{ var3 }}"
- "{{ var4 }}"
- "{{ var5 }}"
- "{{ var6 }}"
- "{{ var7 }}"
- "{{ var8 }}"
結果:
% ansible-playbook test.yml
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match
'all'
PLAY [localhost] *****************************************************************************************************
TASK [Gathering Facts] ***********************************************************************************************
ok: [localhost]
TASK [Print vars] ****************************************************************************************************
ok: [localhost] => (item=True) => {
"msg": true
}
ok: [localhost] => (item=False) => {
"msg": false
}
ok: [localhost] => (item=True) => {
"msg": true
}
ok: [localhost] => (item=False) => {
"msg": false
}
ok: [localhost] => (item=("1" == "1")) => {
"msg": "(\"1\" == \"1\")"
}
ok: [localhost] => (item=("1" == "1")|bool) => {
"msg": "(\"1\" == \"1\")|bool"
}
ok: [localhost] => (item=True) => {
"msg": true
}
ok: [localhost] => (item=True) => {
"msg": true
}
PLAY RECAP ***********************************************************************************************************
localhost : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
| 変数名 | 代入方法 | 結果 |
|---|---|---|
| var1 | True を代入 | boolean true |
| var2 | False を代入 | boolean false |
| var3 | "True" という文字列を代入 | boolean true |
| var4 | "False" という文字列を代入 | boolean false |
| var5 | 条件式を代入 | 条件式の文字列 |
| var6 | 条件式を |bool 付きで代入 |
条件式の文字列 |
| var7 | 条件式を "{{ }}" で囲んで代入 |
boolean true |
| var8 | 条件式に |bool を付けた上で "{{ }}" で囲んで代入 |
boolean true |
条件式を "{{ }}" で囲めば、その結果が boolean として代入されるし、囲まなければ文字列として代入されることがわかります。いずれにせよ、代入の時点で |bool の有無は全く関係ないようです。
when 節への文字列の渡し方
代入時に boolean になっている場合は当然成功するので、ここからは代入時に文字列になってしまった場合のみを考えます。
|bool の有無と、結果が True になるかどうかの4通りで実験しました。Playbook が長くなるので、以下には var1 のタスクだけ記載しています。
---
- hosts: localhost
connection: local
vars:
var1: ("1" == "1")
var2: ("1" == "1")|bool
var3: ("1" == "2")
var4: ("1" == "2")|bool
tasks:
- name: 1. var1 should be printed
debug: msg="{{ var1 }}"
when: var1
- name: 2. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: not var1
- name: 3. var1 should be printed
debug: msg="{{ var1 }}"
when: var1|bool
- name: 4. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: not var1|bool
- name: 5. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: not (var1|bool)
- name: 6. var1 should be printed
debug: msg="{{ var1 }}"
when: "{{ var1 }}"
- name: 7. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: "{{ not var1 }}"
# Template error
# - name: 8. var1 should NOT be printed
# debug: msg="{{ var1 }}"
# when: not "{{ var1 }}"
- name: 9. var1 should be printed
debug: msg="{{ var1 }}"
when: "{{ var1|bool }}"
- name: 10. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: "{{ not var1|bool }}"
- name: 11. var1 should NOT be printed
debug: msg="{{ var1 }}"
when: not "{{ var1|bool }}"
結果はこうなりました。
% ansible-playbook test.yml
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match
'all'
PLAY [localhost] *****************************************************************************************************
TASK [Gathering Facts] ***********************************************************************************************
ok: [localhost]
TASK [1. var1 should be printed] *************************************************************************************
[DEPRECATION WARNING]: evaluating u'var1' as a bare variable, this behaviour will go away and you might need to add
|bool to the expression in the future. Also see CONDITIONAL_BARE_VARS configuration toggle. This feature will be
removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
ok: [localhost] => {
"msg": "(\"1\" == \"1\")"
}
TASK [2. var1 should NOT be printed] *********************************************************************************
skipping: [localhost]
TASK [3. var1 should be printed] *************************************************************************************
skipping: [localhost]
TASK [4. var1 should NOT be printed] *********************************************************************************
ok: [localhost] => {
"msg": "(\"1\" == \"1\")"
}
TASK [5. var1 should NOT be printed] *********************************************************************************
ok: [localhost] => {
"msg": "(\"1\" == \"1\")"
}
TASK [6. var1 should be printed] *************************************************************************************
[WARNING]: conditional statements should not include jinja2 templating delimiters such as {{ }} or {% %}. Found: {{
var1 }}
ok: [localhost] => {
"msg": "(\"1\" == \"1\")"
}
TASK [7. var1 should NOT be printed] *********************************************************************************
[WARNING]: conditional statements should not include jinja2 templating delimiters such as {{ }} or {% %}. Found: {{
not var1 }}
skipping: [localhost]
TASK [9. var1 should be printed] *************************************************************************************
[WARNING]: conditional statements should not include jinja2 templating delimiters such as {{ }} or {% %}. Found: {{
var1|bool }}
skipping: [localhost]
TASK [10. var1 should NOT be printed] ********************************************************************************
[WARNING]: conditional statements should not include jinja2 templating delimiters such as {{ }} or {% %}. Found: {{
not var1|bool }}
ok: [localhost] => {
"msg": "(\"1\" == \"1\")"
}
TASK [11. var1 should NOT be printed] ********************************************************************************
[WARNING]: conditional statements should not include jinja2 templating delimiters such as {{ }} or {% %}. Found: not
"{{ var1|bool }}"
skipping: [localhost]
まとめると、1番の when: varX または 6番の when: {{ varX }} の書き方をすると、DEPRECATION WARNING は出るが、想定通りの結果になりました。それ以外は、文字列の中身に関わらず同じ結果になりました。
| when の書き方 | var1 | var2 | var3 | var4 |
|---|---|---|---|---|
1. varX |
ok | ok | skipping | skipping |
2. not varX |
skipping | skipping | skipping | skipping |
3. varX|bool |
skipping | skipping | skipping | skipping |
4. not varX|bool |
ok | ok | ok | ok |
5. not (varX|bool) |
ok | ok | ok | ok |
6. {{ varX }} |
ok | ok | skipping | skipping |
7. {{ not varX }} |
skipping | skipping | skipping | skipping |
9. {{ varX|bool }} |
skipping | skipping | skipping | skipping |
10. {{ not varX|bool }} |
ok | ok | ok | ok |
11. not {{ varX|bool }} |
skipping | skipping | skipping | skipping |
結局、この DEPRECATION WARNING で |bool を付けろ、と言っている意味はわからずじまいでした。誰か詳しい人いたら教えてください……。
[DEPRECATION WARNING]: evaluating (ansible_distribution_file_variety == "Amazon" and ansible_distribution_major_version == "2") as a bare variable, this behaviour will go away and you might need to add |bool to the expression in the future. Also see CONDITIONAL_BARE_VARS configuration toggle.. This feature will be removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
