ansible-2.2.0.0 group_by intermittent bug

[stanrate]

ISSUE TYPE

• Bug Report

COMPONENT NAME

group_by

ANSIBLE VERSION

ansible 2.2.0.0

CONFIGURATION

OS / ENVIRONMENT

SUMMARY

The problem occurs on 2.2 but not on 2.1
A test case was created containing the following statement:
debug: var=groups['mygroup1']|list
If dynamic host group "mygroup1" created in a previous playbook by the group_by module contains four hosts, four hosts are output by the debug statement. If "mygroup1" contains eight hosts, only the first host is output by the debug statement most of the time but sometimes the second host is output. This is an intermittent problem. The problem does not occur when the host group contains 3 or 4 hosts but always occurs when the group contains 7 or 8 hosts.

STEPS TO REPRODUCE

• name: Populate host group with host names

hosts: host1:host2:host3:host4

hosts: host1:host2:host3:host4:host5:host6:host7:host8
gather_facts: no
tasks:

• name: task1
  group_by: key='mygroup1'

• name: Run playbook on all hosts in host group "mygroup1"
  hosts: mygroup1
  gather_facts: no
  tasks:

  • name: task1
    debug: var=inventory_hostname

• name: Show hosts in host group "mygroup1"
  hosts: localhost
  gather_facts: no
  tasks:

  • name: task1
    debug: var=groups['mygroup1']|list

EXPECTED RESULTS

TASK [task1] *******************************************************************
ok: [localhost] => {
"groups['mygroup1']|list": [
"host1",
"host2",
"host3",
"host4",
"host5",
"host6",
"host7",
"host8",
]
}

ACTUAL RESULTS

TASK [task1] *******************************************************************
ok: [localhost] => {
    "groups['mygroup1']|list": [
        "host1", 
    ]
}

[stanrate]

Since upgrading from Ansible 2.1 to 2.2, several playbooks that use the "group_by" module do not produce the correct results because variable substitution using the dynamic host group does not result in a complete list of hostnames. Most of the time, ansible only produces output for the first host in the host group and ignores the rest of the hosts. When using jinja2 filters as in the following example, ansible only processes the first host in dynamic host group x created by the group_by module:
{{ groups['x']|list }}
Note that the bug does not occur if the dynamic host group contains a small number of hosts e.g. 2, 3 or 4 hosts. The bug occurs when the dynamic host group contains a larger number of hosts e.g. 7, 8 or 9 hosts.

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[stanrate]

A workaround is to use the add_host module rather than the group_by module (broken in Ansible 2.2) to create a dynamic adhoc host group. The playbook worked correctly after the following line:

group_by: key='mygroup1'

was replaced with:

add_host: hostname={{item}} groups='mygroup1'
with_items: "{{ansible_play_hosts}}"

[ansibot]

This issue was migrated to ansible/ansible#29452