Ansible known_hosts module with non-standard port - ansible

Question

I'm provisioning a new server, and want to automatically add its public key to my local known_hosts file. My server is running on port 2222.
hosts:
[remotes]
my_server ansible_host:42.42.42.42 ansible_port:2222
playbook.yml:
---
hosts: all
gather_facts: no
tasks:
- name: get host key
local_action: command ssh-keyscan -t rsa -p {{ansible_port}} -H {{ansible_host}}
register: host_key
- name: add host key
when: host_key is success
delegate_to: localhost
known_hosts:
name: "{{item}}"
state: present
hash_host: yes
key: "{{host_key.stdout}}"
with_items:
- "{{ansible_host}}"
- "{{inventory_hostname}}"
This adds new entries to the known_hosts.
BUT ssh 42.42.42.42:2222 and ssh my_server:2222 still show the unknown key warning.
I suspect it's because 1) I'm running on a non-standard port (the docs for the known_host module don't show an option for setting the port), or 2) something to do with the hashing option.
How do I do this?

Answer 1

I found a solution buried in an old issue. The trick is to use [host]:port instead of host.
---
hosts: all
gather_facts: no
tasks:
# add entry to known_hosts for server's IP address
- name: get host key
local_action: command ssh-keyscan -t rsa -p {{ansible_port}} -H {{ansible_host}}
register: host_key
- name: add host key
when: host_key is success
delegate_to: localhost
known_hosts:
name: "[{{ansible_host}}]:{{ansible_port}}" # <--- here
state: present
hash_host: yes
key: "{{host_key.stdout}}"
# add entry to known_hosts for server's hostname
- name: get host key
local_action: command ssh-keyscan -t rsa -p {{ansible_port}} -H {{inventory_hostname}}
register: host_key
- name: add host key
when: host_key is success
delegate_to: localhost
known_hosts:
name: "[{{inventory_hostname}}]:{{ansible_port}}" # <--- here
state: present
hash_host: yes
key: "{{host_key.stdout}}"
I couldn't find a way to avoid the repetition, because with_items can't be applied to multiple tasks at once, so it's ugly but it works.
This allows ssh 42.42.42.42:2222 and ssh my_server:2222 without prompts (though my_server must be defined in /etc/hosts and/or ~/.ssh/config).