Ansible loop sequentially with_nested multiple array

Question

I want to use with_nested but with 2 different array sequentially,

devices:

• data: /dev/vdb
• data: /dev/vdc

hostname:

• host1
• host2
• host3

I was trying use this way

- name: debug
  debug: msg="{{ item[0] }} {{ item[1] }}"
  with_nested:
    - "{{ devices }}"
    - "{{ hostname }}"

But the result like this :

- /dev/vdb host1
- /dev/vdb host2
- /dev/vdb host3
- /dev/vdc host1
- /dev/vdc host2
- /dev/vdc host3

I expected result like this:

- /dev/vdb host1
- /dev/vdc host1
- /dev/vdb host2
- /dev/vdc host2
- /dev/vdb host3
- /dev/vdc host3

Answer 1

It's a nested look, equivalent to:

for item0 in devices: for item1 in hostname: print(item0, item1)

For each item in devices, it will iterate over all the items in hostname...giving exactly the results you've described. You're still getting the same list of pairs that you expect, just in a different order.

If you reverse the arguments to with_nested, like this:

    - name: debug
      debug:
        msg: "{{ item[0] }} {{ item[1] }}"
      with_nested:
        - "{{ hostname }}"
        - "{{ devices }}"

You'll get the pairs in the order you want, albeit swapped:

PLAY [localhost] *****************************************************************************************************************************************************************************

TASK [debug] *********************************************************************************************************************************************************************************
ok: [localhost] => (item=['host1', '/dev/vdb']) => {
    "msg": "host1 /dev/vdb"
}
ok: [localhost] => (item=['host1', '/dev/vdc']) => {
    "msg": "host1 /dev/vdc"
}
ok: [localhost] => (item=['host2', '/dev/vdb']) => {
    "msg": "host2 /dev/vdb"
}
ok: [localhost] => (item=['host2', '/dev/vdc']) => {
    "msg": "host2 /dev/vdc"
}
ok: [localhost] => (item=['host3', '/dev/vdb']) => {
    "msg": "host3 /dev/vdb"
}
ok: [localhost] => (item=['host3', '/dev/vdc']) => {
    "msg": "host3 /dev/vdc"
}

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