Ansible how to set_fact with condition or var base on condition - ansible

Question

I have 3 types of servers: dev, qa and prod. I need to send files to server specific home directories, i.e:
Dev Home Directory: /dev/home
QA Home Directory:/qa/home
PROD Home Directory: /prod/home
I have var set as boolean to determine the server type and think of using set_fact with condition to assign home directories for the servers. My playbook looks like this:
---
- hosts: localhost
var:
dev: "{{ True if <hostname matches dev> | else False }}"
qa: "{{ True if <hostname matches qa> | else False }}"
prod: "{{ True if <hostname matches prod> | else False }}"
tasks:
- set_facts:
home_dir: "{{'/dev/home/' if dev | '/qa/home' if qa | default('prod')}}"
However, then I ran the playbook, I was getting error about 'template expected token 'name', got string> Anyone know what I did wrong? Thanks!

Answer 1

Use match test. For example, the playbook
shell> cat pb.yml
- hosts: localhost
vars:
dev_pattern: '^dev_.+$'
qa_pattern: '^qa_.+$'
prod_pattern: '^prod_.+$'
dev: "{{ hostname is match(dev_pattern) }}"
qa: "{{ hostname is match(qa_pattern) }}"
prod: "{{ hostname is match(prod_pattern) }}"
tasks:
- set_fact:
home_dir: /prod/home
- set_fact:
home_dir: /dev/home
when: dev|bool
- set_fact:
home_dir: /qa/home
when: qa|bool
- debug:
var: home_dir
gives (abridged)
shell> ansible-playbook pb.yml -e hostname=dev_007
home_dir: /dev/home
Notes:
The variable prod is not used because /prod/home is default.
prod/home is assigned to home_dir first because it's the default. Next tasks can conditionally overwrite home_dirs.
Without the variable hostname defined the playbook will crash.
A simpler solution that gives the same result is creating a dictionary of 'pattern: home_dir'. For example
- hosts: localhost
vars:
home_dirs:
dev_: /dev/home
qa_: /qa/home
prod_: /prod/home
tasks:
- set_fact:
home_dir: "{{ home_dirs|
dict2items|
selectattr('key', 'in' , hostname)|
map(attribute='value')|
list|
first|default('/prod/home') }}"
- debug:
var: home_dir

Answer 2

Adding an alternative method to achieve this. This kind of extends the group_vars suggestion given by #mdaniel in his comment.
Ansible has a ready-made mechanism to build the variables based on the inventory hosts and groups. If you organize your inventory, you can avoid a lot of complication in trying to match host patterns.
Below is a simplified example, please go through the link above for more options.
Consider an inventory file /home/user/ansible/hosts:
[dev]
srv01.dev.example
srv02.dev.example
[qa]
srv01.qa.example
srv02.qa.example
[prod]
srv01.prod.example
srv02.prod.example
Using group_vars:
Then you can have below group_var files in /home/user/ansible/group_vars/ (matching inventory group names):
dev.yml
qa.yml
prod.yml
In dev.yml:
home_dir: "/dev/home"
In qa.yml:
home_dir: "/qa/home"
In prod.yml:
home_dir: "/prod/home"
Using host_vars:
Or you can have variables specific to hosts in host_vars directory /home/user/ansible/host_vars/:
srv01.dev.example.yml
srv01.prod.example.yml
# and so on
In srv01.dev.example.yml:
home_dir: "/dev/home"
In srv01.prod.example.yml:
home_dir: "/prod/home"
These variables will be picked based on which hosts you run the playbook, for example the below playbook:
---
- hosts: dev
tasks:
- debug:
var: home_dir
# will be "/dev/home"
- hosts: prod
tasks:
- debug:
var: home_dir
# will be "/prod/home"
- hosts: srv01.dev.example
tasks:
- debug:
var: home_dir
# will be "/dev/home"
- hosts: srv01.prod.example
tasks:
- debug:
var: home_dir
# will be "/prod/home"