CODEWITHSUNDEEP
ansibleyamljinja2
user3925030
user3925030

Reputation: 87

Choosing host from inventory group based on a host variable

I have an ansible inventory file that looks like this:

[web]
web1.so.com tech=apache
web2.so.com tech=nginx

I'd like to list the web hosts in a config file only if the tech is nginx. So in this case i'd like the ansible template to produce the below in the config file.

server: web2.so.com

How can I get ansible to insert web hosts only if tech=nginx?

I would usually access hosts by setting using groups in the ansible template:

server: "{{groups['web']}}"

But i'm aware this will list all of the hosts in the web group.

I can't figure out how to only choose hosts that have tech=nginx, and in this use case it's not possible to split them up into web-nginx and web-apache groups.

It's also not possible to hardcode it to use web2 as the apache host could change with each rebuild.

Upvotes: 0

Views: 1197

Answers (2)

Zeitounator
Zeitounator

Reputation: 44799

You can create groups dynamically with the add_host or group_by modules.

In your case, using group_by as in the following example should meet your requirements:

---
- name: Create dynamic tech groups
  hosts: all
  gather_facts: false

  tasks:
    - name: Create the groups depending on tech
      group_by:
        key: "tech_{{ tech }}"
      when: tech is defined

- name: Do something on nginx group
  hosts: tech_nginx
  gather_facts: false

  tasks:
    - name: Show it works
      debug:
        msg: "I'm running on {{ inventory_hostname }}"

Of course, once this is done, you can use groups['tech_nginx'] elsewhere in your playbook to get the list of hosts in that group.

Upvotes: 1

Vladimir Botka
Vladimir Botka

Reputation: 68189

Q: "List the web hosts in a config file only if the tech is nginx."

A: It is possible to use json_query. For example the play below

- hosts: all
  tasks:
    - set_fact:
        nginx_list: "{{ hostvars|dict2items|
                        json_query('[?value.tech==`nginx`].key') }}"
      run_once: true
    - debug:
        var: nginx_list

gives the variable nginx_list which can be used in the configuration.

ok: [web1.so.com] => {
    "nginx_list": [
        "web2.so.com"
    ]
}
ok: [web2.so.com] => {
    "nginx_list": [
        "web2.so.com"
    ]
}

For example lineinfile below

- lineinfile:
    path: /tmp/webservers.cfg
    regex: "^nginx\\s*=(.*)$"
    line: "nginx = {{ nginx_list|join(', ') }}"
    create: true
  delegate_to: localhost

gives

$ cat /tmp/webservers.cfg 
nginx = web2.so.com

Upvotes: 0

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