Ansible concat vars to string - ansible

Question

I've spent most of the day trying to solve this problem and have thus far failed. I am building some playbooks to automate functions in Splunk, and am attempting to convert a list of hosts from an inventory group E.G.
[search_head]
1.2.3.4
5.6.7.8
My expected (desired) result from the debug output of the play should be:
https://1.2.3.4:8089, https://5.6.7.8:8089
I am attempting to complete this by running the following playbook against a running host:
---
- name: Build search head list to initialize the captain
hosts: search_head
remote_user: ansible
vars:
inventory_file: ./inventory-ec2-single-site
search_head_uri: "{{ lookup('template', './bootstrap-sh-deployer.j2') }}"
pre_tasks:
- include_vars:
dir: 'group_vars'
extensions:
- yml
- yaml
tasks:
- name: dump array
debug:
msg: "{{ search_head_uri }}"`
With the template bootstrap-sh-deployer.j2:
{%- set search_head_uri = [] %}
{% for host in groups['search_head'] %}
{%- if search_head_uri.append("https://{{ host }}:8089") %}
{%- endif %}
{%- if not loop.last %}, {% endif -%}
{%- endfor %}
However, the current play returns search_head_uri: ", " which tells me that the loop is running, but {{ host }} is not resolving.

Answer 1

Once you open a Jinja2 expression or a statement you should use Jinja2 syntax. You cannot nest them (i.e. you can't use {{ }} inside {% %}).
{%- if search_head_uri.append("https://" + host + ":8089") %}

Answer 2

This worked - Combination of the answer above to fix jinja formatting and using hostvars to get to the ansible_nodename.
{%- set search_head_uri = [] %}
{% for host in groups['search_head'] %}
{{ "https://" + hostvars[host]['ansible_nodename'] + ":8089" }}
{%- if not loop.last %}, {% endif -%}
{%- endfor %}