Ansible: how to construct a variable from another variable and then fetch it's value

Question

Here is my problem I need to use one variable \'target_host\' and then append \'_host\' to it\'s value to get another variable name whose value I need. If you look at my pl

Answer 1

You have two ways to choose:
1. General using.

vars:
    - target_host: smtp
    - smtp: smtp.max.com
tasks: 
    - name: testing
        debug: msg={{ target_host }}
    - name: testing
        debug: msg={{ smtp }}
    - name: testing
        debug: msg={{ vars[target_host] }}

2. Using fact

tasks: 
    - set_fact: target_host=smtp
    - set_fact: smtp=smtp.max.com
    - name: testing
        debug: msg={{ target_host }}
    - name: testing
        debug: msg={{ smtp }}
    - name: testing
        debug: msg={{hostvars[inventory_hostname][target_host]}}

Answer 2

If you have a variable like

vars: myvar: xxx xxx_var: anothervalue

the working Ansible syntax:

- debug: msg={{ vars[myvar + '_var'] }}

will give you the analogue of:

- debug: msg={{ xxx_var }}

Answer 3

You can try global array var:

regions:
  us-east-1:
    endpoint: rds.us-east-1.amazonaws.com
  cn-north-1:
    endpoint: rds.cn-north-1.amazonaws.com.cn
  cn-northwest-1:
    endpoint: rds.cn-northwest-1.amazonaws.com.cn

And use it to get value depending of another:

region_endpoint: "{{ regions[region].endpoint}}"

In your case:

target_host:
  imap:
    host: imap.max.com
  smtp:
    host: smtp.max.com

then:

region_endpoint: "{{ target_host[service].host}}"

Answer 4

There are many answers above. It helped me a lot. But i have not found a single answer how to keep these variable in vars-> main.yml file. So you have to create a dictionary in vars-> main.yml file.

vars -> main.yml file

cassandra_version: 2.1.16
file_sha_cassandra: "apache-cassandra-{{ cassandra_version }}_sha256"
# Create Dictionary here
cassandra:
    apache-cassandra-2.1.16_sha256: "sha256: checksum_of_file"
    ##Add more variable

Now you have to call this in task -> main.yml file:

---
  - name: Down load Cassandra Binaries
    get_url:
       url: "file_url"
       dest: "{{ base_directory }}"
       checksum: "{{ cassandra[file_sha_cassandra] }}"
       timeout: 800

Answer 5

You can use "hostvars" to pass the variable, host facts can be loaded from group vars or host vars

yml

---
- name: "Play to for dynamic groups"
  hosts: x0
  vars:
    - target_host: smtp
  tasks:
    - set_fact: smtp_host="smtp.max.com"
    - set_fact: host_var_name={{target_host}}_host
    - set_fact: dym_target_host={{hostvars[inventory_hostname][host_var_name]}}

    - name: testing
      debug: msg={{ target_host }}
    - name: testing
      debug: msg={{ smtp_host }}
    - name: testing
      debug: msg={{ target_host }}_host
    - name: testing
      debug: msg={{ dym_target_host }}

output:

PLAY [Play to for dynamic groups] *********************************************

GATHERING FACTS ***************************************************************
ok: [x0]

TASK: [set_fact smtp_host="smtp.max.com"] *************************************
ok: [x0]

TASK: [set_fact host_var_name=smtp_host] **************************************
ok: [x0]

TASK: [set_fact dym_target_host={{hostvars[inventory_hostname][host_var_name]}}] ***
ok: [x0]

TASK: [testing] ***************************************************************
ok: [x0] => {
    "msg": "smtp"
}

TASK: [testing] ***************************************************************
ok: [x0] => {
    "msg": "smtp.max.com"
}

TASK: [testing] ***************************************************************
ok: [x0] => {
    "msg": "smtp_host"
}

TASK: [testing] ***************************************************************
ok: [x0] => {
    "msg": "smtp.max.com"
}

PLAY RECAP ********************************************************************
x0                         : ok=8    changed=0    unreachable=0    failed=0

Answer 6

You need to put quotes around it:

- hosts: local
  vars: [ target_host: smtp ]
  tasks:
    debug: msg="{{ target_host }}_host"

-- edit --

Kashyap I need to go one more level than this. Imagine there is another variable 'smtp_host' and I want to construct that variable at runtime using another variable(target_host) and attaching a string '_host' to it. = {{ {{ target_host }}_host }} – Max

My bad. Didn't read carefully enough.

This (AFAIK) isn't possible. The primary limitation that stops us doing this (no matter how you spin it), is 'variable expansion' in ansible is a single pass process and what you want requires multiple-passes.

Only [seriously hacky] ways I can think of are:

• Create the playbook dynamically from your playbook using template and execute it.
• I heard that Jinja2 engine does multi-pass evaluation. May be if you put these strings in a template and then use the lookup('template', ...) filter. Unfortunately I have no experience with Jinja2 templates so not quite sure if this is even an option.