Ansible docker_container etc_hosts with variable key - docker

Question

I've an ansible script through which I spawn a docker container and add few hosts entries to it, since etc_hosts takes key as host name and corresponding IP address. In my case I need to have both host name and IP address to be driven by some variable, for instance
docker_container:
name: image-name
image: image-to-be-pulled
state: started
restart_policy: always
etc_hosts:
"{{ domain_1 }}": "{{ domain_1_ip }}"
domain_2 : "{{ domain_2_ip }}"
domain_3 : "{{ domain_3_ip }}"
When I make above configuration then it makes an entry to host file as
xx.xx.xx.xxx {{ domain_1 }}
Ideally the the host file should contain host name against the IP, can someone suggest how can i achieve this. Thanks in advance

Answer 1

Try this syntax:
docker_container:
name: image-name
image: image-to-be-pulled
state: started
restart_policy: always
etc_hosts: >
{
"{{ domain_1 }}": "{{ domain_1_ip }}",
"domain_2" : "{{ domain_2_ip }}",
"domain_3" : "{{ domain_3_ip }}"
}
This will form dict-like string that ansible's templator will evaluate into dict.
Pay attention, that every item should be quoted and pairs are separated by commas.

Answer 2

I had success with...
in my play(book):
- vars:
my_etc_hosts:
{
"host1.example.com host1": 10.3.1.5,
"host2.example.com host2": 10.3.1.3
}
(no ">" character, compared to the accepted answer)
Separated from the playbook, the role with...
in the task:
- name: have the container created
docker_container:
etc_hosts: "{{ my_etc_hosts | default({}) }}"
in defaults/main.yml:
my_etc_hosts: {}
Additionally (not needed by the task above, but part of another template task):
in a template, with jinja2:
{% for host in my_etc_hosts | default([]) %}
--add-host "{{ host }}":{{ my_etc_hosts[host] }} \
{% endfor %}
(As a plus, you see how two hostnames for one IP address can be handled: "fqdn alias1". If you instead split them into two values, they will form two lines in /etc/hosts with the same IP, which is not correct according to the man page.)