haproxy implementation - generation of "backend servers" from groups of hosts

Issue

This is the result of my template receiving the variable haproxy_services:

backend galera-back
  server aio1_galera_container-b5f33b58 {# hostvars[aio1_galera_container-b5f33b58]["ansible_ssh_host"] #}:3306 check port 3306 inter 3306 rise 1 fall 1

Which is problematic, I'd like to have the ip instead of a string "{# hostvars[aio1_galera_container-b5f33b58]["ansible_ssh_host"] #}"
It's because I can't use {{ }} inside a filter. So what should I do?

plugins-filter-haproxy.py

def haproxy_backend_servers(servers_group, default_port, params=False, connection='ansible_ssh_host'):
    """Return a list of dicts of servers from a group (servers_group), and
    formatted for haproxy backend usage. Each item of the list is a server,
    with its name, ip, port and parameters.

    :param servers_group: Ansible group name
    :type servers_group: ``list``
    :param default_port: port to service is listening on in the backend network
    :type default_port: ``int``
    :param params: list of params to pass into haproxy.
    :type params: ``list``
    :param connection: Network connection name.
    :type connection: ``str``
    :returns: ``list``
    """

    if params is False:
        params = [ "check port %s" % ( default_port ) , "inter {{ haproxy_default_interval }}" , "rise %s" % ( len(servers_group) ) , "fall %s"  % ( len(servers_group) ) ]

    return_list = list()
    for server in servers_group:
        entry = {
            'name': server,
            'ip': '{{ hostvars[%s]["%s"] }}:%s' % (
                server, connection, default_port
            ),
            """'ip': "%s:%s" % ( hostvars[server][connection] , default_port )
            ,"""
            'params': params
        }
        return_list.append(entry)
    else:
        return return_list

vars-haproxy_services_example.yml

galera_params:
  - check port 3306
  - rise 1
  - fall 1
galera_default_port: 3306
haproxy_services:
  galera:
    frontends:
      - name: galera
        binds:
          - ip: '*:3306'
        balance_type: 'tcp'
        options:
          - tcplog
        timeout_client: 5000s
        default_backend: galera-back
    backends:
      - name: galera-back
        balance_type: tcp
        balance: leastconn
        options:
          - "mysql-check user monitoring"
        timeout_server: 5000s
        servers: "{{ groups['galera_all'][0:1] | haproxy_backend_servers(galera_default_port,galera_params) }}"
        backups: "{{ groups['galera_all'][1:] | haproxy_backend_servers(galera_default_port,galera_params) }}"

I didn't paste the template, but it's basically there: https://github.com/evrardjp/ansible-haproxy/blob/master/templates/service.j2
and the task running the template is here: https://github.com/evrardjp/ansible-haproxy/blob/master/tasks/haproxy_post_install.yml#L47-L51