Getting changed/failed hosts list from a previous task | Ansible - ansible

Question

All,
Example: If i've got 20 hosts for a playbook and running them with Serial:10, below shell command runs on 10 hosts at a time. Once done handler task is called, wherein the task which creates dict (_dict) doesn't give a dictionary output thus the second task - Failed host - failed with mentioned error.
- name: Run some shell command
shell: "echo 2 > /abcd/abcd.txt"
when: random condition is satisfied
register: update2
ignore_errors: yes
notify: abc_handler
- handler:
- name: abcd_handler
set_fact:
_dict: "{{ dict(ansible_play_hosts|zip(
ansible_play_hosts|map('extract', hostvars, 'update2'))) }}"
run_once: true
- name: Find failed hosts
set_fact:
_failed: "{{ _dict|dict2items|json_query('[?value.failed].key') }}"
run_once: true
Handler First task output:
"changed: false"
"ansible_facts": {
"_dict": "{u'host1': {'stderr_lines': [], u'changed': True,...u'host2':.....u'host10'}"
2nd handler task gives the mentioned error when the dict2items is run for above values.
Thank you.

Answer 1

Q: "List of hosts where a certain task executed, changed something, or got failed."
A: For example, the command makes no changes at test_11 changes the file at test_12, and fails at test_13
- hosts: test_11,test_12,test_13
tasks:
- shell:
cmd: "echo 2 > /tmp/test/abcd.txt"
creates: /tmp/test/abcd.txt
register: update1
ignore_errors: true
TASK [shell] ***********************************************************
changed: [test_12]
fatal: [test_13]: FAILED! => changed=true
cmd: echo 2 > /tmp/test/abcd.txt
delta: '0:00:00.045992'
end: '2021-04-25 23:22:31.623804'
msg: non-zero return code
rc: 2
start: '2021-04-25 23:22:31.577812'
stderr: '/bin/sh: cannot create /tmp/test/abcd.txt: Permission denied'
stderr_lines: <omitted>
stdout: ''
stdout_lines: <omitted>
...ignoring
ok: [test_11]
Let's create a dictionary with the data first, e.g.
- set_fact:
_dict: "{{ dict(ansible_play_hosts|
zip(ansible_play_hosts|
map('extract', hostvars, 'update1'))) }}"
run_once: true
gives
_dict:
test_11:
changed: false
cmd: echo 2 > /tmp/test/abcd.txt
failed: false
rc: 0
stdout: skipped, since /tmp/test/abcd.txt exists
stdout_lines:
- skipped, since /tmp/test/abcd.txt exists
test_12:
changed: true
cmd: echo 2 > /tmp/test/abcd.txt
delta: '0:00:00.032474'
end: '2021-04-25 23:14:36.361510'
failed: false
rc: 0
start: '2021-04-25 23:14:36.329036'
stderr: ''
stderr_lines: []
stdout: ''
stdout_lines: []
test_13:
changed: true
cmd: echo 2 > /tmp/test/abcd.txt
delta: '0:00:00.054980'
end: '2021-04-25 23:14:35.565811'
failed: true
msg: non-zero return code
rc: 2
start: '2021-04-25 23:14:35.510831'
stderr: '/bin/sh: cannot create /tmp/test/abcd.txt: Permission denied'
stderr_lines:
- '/bin/sh: cannot create /tmp/test/abcd.txt: Permission denied'
stdout: ''
stdout_lines: []
Note that test_11 is reported ok not skipped despite the registered variable showing "stdout: skipped, since /tmp/test/abcd.txt exists".
The analysis is now trivial, e.g.
- set_fact:
_failed: "{{ _dict|dict2items|json_query('[?value.failed].key') }}"
run_once: true
gives the list of the failed hosts
_failed:
- test_13
and the next task
- set_fact:
_changed: "{{ (_dict|dict2items|json_query('[?value.changed].key'))|
difference(_failed) }}"
_ok: "{{ _dict|dict2items|json_query('[?value.changed == `false`].key') }}"
run_once: true
gives
_changed:
- test_12
_ok:
- test_11
Note that
The failed hosts need to be subtracted from the changed hosts because failed hosts are also reported as changed.
There will be no registered variable if a task is skipped.
Serial
Split the playbook into 2 plays if serial is used. e.g.
shell> cat playbook.yml
- hosts: all
serial: 10
tasks:
- shell:
cmd: "echo 2 > /tmp/test/abcd.txt"
creates: /tmp/test/abcd.txt
register: update1
ignore_errors: true
- hosts: all
tasks:
- set_fact:
_dict: "{{ dict(ansible_play_hosts|zip(
ansible_play_hosts|map('extract', hostvars, 'update1'))) }}"
run_once: true

Answer 2

It seems you would like to get the hosts on which the command task (shown in the question) failed or changed, and then target them for some other tasks.
There are two things required for this:
If the command task fails, playbook execution will stop and hence none of the following tasks will run. So we need to add ignore_errors flag to the task
add_host module to create a new group of hosts when the task failed or changed
So finally tasks like below should do the trick:
- hosts: some_group
serial: 1
- name: update file count
shell: "echo 2 > /home/ec2-user/abcd.txt"
when:
- count.stdout == "1"
register: update1
ignore_errors: true
- name: conditionally add the hosts from current play hosts to a new group
add_host:
groups:
- new_group
host: "{{ ansible_hostname }}"
when: >
cmd_stat is failed or
cmd_stat is changed
# Then have a play targeting the new group
- hosts: new_group
tasks:
# Tasks to be performed
Though the use of serial might make the whole playbook run longer if there are lot of hosts.