Ansible role of duplicate works for the absolute parameters only - ansible

Question

I have playbook like this
test_playbook/
├── dep_test.yaml
├── my_hosts_file
└── roles
├── common
│   └── vars
│   └── main.yaml
├── dep_test
│   ├── meta
│   │   └── main.yaml
│   └── tasks
│   └── main.yaml
├── dep_test_a
│   └── tasks
│   └── main.yaml
└── dep_test_b
├── meta
│   └── main.yaml
└── tasks
└── main.yaml
Files content are as below.
dep_test.yaml
- hosts: my_host
gather_facts: no
roles:
- common
- dep_test
my_hosts_file
[my_host]
localhost
roles/common/vars/main.yaml
python_version: "3"
roles/dep_test/tasks/main.yaml
- name: debug test
debug:
msg: test debug
roles/dep_test/meta/main.yaml
dependencies:
- role: dep_test_a
# pyenv_versions: ["{{ python_version }}"]
pyenv_versions: ["3"]
- role: dep_test_b
# python_versions: ["{{ python_version }}"]
python_versions: ["3"]
roles/dep_test_a/tasks/main.yaml
- name: Dep test a
debug:
msg: "Dependency test a called with {{ pyenv_versions }}"
roles/dep_test_b/tasks/main.yaml
- name: Dep test b
debug:
msg: "Dependency test b called with {{ python_versions }}"
roles/dep_test_b/meta/main.yaml
dependencies:
- role: dep_test_a
# pyenv_versions: "{{ python_versions }}"
pyenv_versions: ["3"]
When I pass parameter as ["3"] it works fine and apply the Role Duplication and Execution
ansible-playbook dep_test.yaml -i my_hosts_file -u root --ask-pass
SSH password:
PLAY [my_host] ****************************************************************************************************
TASK [dep_test_a : Dep test a] ************************************************************************************
ok: [localhost] => {
"msg": "Dependency test a called with [u'3']"
}
TASK [dep_test_b : Dep test b] ************************************************************************************
ok: [localhost] => {
"msg": "Dependency test b called with [u'3']"
}
TASK [dep_test : debug test] **************************************************************************************
ok: [localhost] => {
"msg": "test debug"
}
PLAY RECAP ********************************************************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=0
When I change the parameter from ["3"] to use the variable form common/vars/main.yaml's python_version, it fail the Duplication rule and execute same role with duplicate arguments.
After change code would be
roles/dep_test/meta/main.yaml
dependencies:
- role: dep_test_a
pyenv_versions: ["{{ python_version }}"]
# pyenv_versions: ["3"]
- role: dep_test_b
python_versions: ["{{ python_version }}"]
# python_versions: ["3"]
roles/dep_test_b/meta/main.yaml
dependencies:
- role: dep_test_a
pyenv_versions: "{{ python_versions }}"
# pyenv_versions: ["3"]
Playbook execution output.
ansible-playbook dep_test.yaml -i my_hosts_file -u root --ask-pass
SSH password:
PLAY [my_host] ****************************************************************************************************
TASK [dep_test_a : Dep test a] ***********************************************************************************
ok: [localhost] => {
"msg": "Dependency test a called with [u'3']"
}
TASK [dep_test_a : Dep test a] ************************************************************************************
ok: [localhost] => {
"msg": "Dependency test a called with [u'3']"
}
TASK [dep_test_b : Dep test b] ************************************************************************************
ok: [localhost] => {
"msg": "Dependency test b called with [u'3']"
}
TASK [dep_test : debug test] **************************************************************************************
ok: [localhost] => {
"msg": "test debug"
}
PLAY RECAP ********************************************************************************************************
localhost : ok=4 changed=0 unreachable=0 failed=0
Role dep_test_a called 2 times with same arguments [u'3']
TASK [dep_test_a : Dep test a] ***********************************************************************************
ok: [localhost] => {
"msg": "Dependency test a called with [u'3']"
}
TASK [dep_test_a : Dep test a] ************************************************************************************
ok: [localhost] => {
"msg": "Dependency test a called with [u'3']"
}
One for the dependencies in dep_test role and another for dep_test_b.
As per the rule of dependencies, this should be called only once.
Question: Why dependent role runs twice when passing the parameter?

Answer 1

Question: Why dependent role runs twice when passing the parameter?
Answer: Because Ansible uses lazy evaluation, hence Jinja2 templating is not being triggered until the variable is used.
Passing a variable to a role is not considered a usage, so it passes and compares the templates, not the values.
You call the dep_test_a role twice:
- role: dep_test_a
pyenv_versions: ["{{ python_version }}"]
and:
- role: dep_test_a
pyenv_versions: "{{ python_versions }}"
["{{ python_version }}"] is not equal to "{{ python_versions }}", thus Ansible executes the role twice.
And btw, the code to illustrate the behaviour in the question can be shortened to:
- hosts: localhost
connection: local
gather_facts: no
vars:
my_var1: 1
my_var2: 1
roles:
- role: my_role
role_param: "{{ my_var1 }}"
- role: my_role
role_param: "{{ my_var2 }}"