HAProxy rules for Horizon emit warnings when using "split" HAProxy config template

[Jason Anderson]

**Bug Report**

What happened:

When using the "haproxy_single_service_split.cfg.j2" template for the `haproxy_service_template` var, HAProxy will emit warnings upon startup around the Horizon section:

  [WARNING] 103/153158 (35) : parsing [/etc/haproxy/services.d/horizon.cfg:4] : 'balance' ignored because frontend 'horizon_external_front' has no backend capability.
  [WARNING] 103/153158 (35) : parsing [/etc/haproxy/services.d/horizon.cfg:22] : 'balance' ignored because frontend 'horizon_front' has no backend capability.

What you expected to happen:

No warnings are emitted by HAProxy.

How to reproduce it (minimal and precise):

Set these vars:

enable_horizon: yes
enable_haproxy: yes
haproxy_service_template: "haproxy_single_service_split.cfg.j2"

Then deploy/reconfigure HAProxy.

**Environment**:
* OS (e.g. from /etc/os-release): CentOS 7
* Kernel (e.g. `uname -a`): Linux 3.10.0-1062.1.2.el7.x86_64
* Docker version if applicable (e.g. `docker version`): 19.03.3
* Kolla-Ansible version (e.g. `git head or tag or stable branch` or pip package version if using release): stable/train
* Docker image Install type (source/binary): source
* Docker image distribution: centos
* Are you using official images from Docker Hub or self built? self-built (Kolla stable/train)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/719677
Committed: https://git.openstack.org/cgit/openstack/kolla-ansible/commit/?id=5c760df3d5f1886290b8dd86eb515acc06e66c9a
Submitter: Zuul
Branch: master

commit 5c760df3d5f1886290b8dd86eb515acc06e66c9a
Author: Jason Anderson <email address hidden>
Date: Mon Apr 13 15:06:00 2020 -0500

    [horizon] Move 'balance' HAProxy keyword

    The "balance" keyword is not valid in a frontend section. From the
    HAProxy documentation[1]:

    balance <algorithm> [ <arguments> ]
    balance url_param <param> [check_post [<max_wait>]]
      Define the load balancing algorithm to be used in a backend.
      May be used in sections : defaults | frontend | listen | backend
                                     yes | no | yes | yes

    When running HAProxy using the "split" template style, where a
    frontend/backend pair are used instead of one listen section, HAProxy
    will emit warnings for the Horizon config due to this.

    [1]: https://www.haproxy.org/download/1.5/doc/configuration.txt

    Closes-Bug: #1872540
    Change-Id: I91cee275d91a51944298618493f4ea0cd80282cc

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/train
Review: https://review.opendev.org/720516

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/stein
Review: https://review.opendev.org/720517

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/720516
Committed: https://git.openstack.org/cgit/openstack/kolla-ansible/commit/?id=b18d3b5bc5cc4daa63f3bdde7dd7179c4eefee63
Submitter: Zuul
Branch: stable/train

commit b18d3b5bc5cc4daa63f3bdde7dd7179c4eefee63
Author: Jason Anderson <email address hidden>
Date: Mon Apr 13 15:06:00 2020 -0500

    [horizon] Move 'balance' HAProxy keyword

    The "balance" keyword is not valid in a frontend section. From the
    HAProxy documentation[1]:

    balance <algorithm> [ <arguments> ]
    balance url_param <param> [check_post [<max_wait>]]
      Define the load balancing algorithm to be used in a backend.
      May be used in sections : defaults | frontend | listen | backend
                                     yes | no | yes | yes

    When running HAProxy using the "split" template style, where a
    frontend/backend pair are used instead of one listen section, HAProxy
    will emit warnings for the Horizon config due to this.

    [1]: https://www.haproxy.org/download/1.5/doc/configuration.txt

    Closes-Bug: #1872540
    Change-Id: I91cee275d91a51944298618493f4ea0cd80282cc
    (cherry picked from commit 5c760df3d5f1886290b8dd86eb515acc06e66c9a)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/720517
Committed: https://git.openstack.org/cgit/openstack/kolla-ansible/commit/?id=6450daba07256eb394930657d293ea6a6cb80ef6
Submitter: Zuul
Branch: stable/stein

commit 6450daba07256eb394930657d293ea6a6cb80ef6
Author: Jason Anderson <email address hidden>
Date: Mon Apr 13 15:06:00 2020 -0500

    [horizon] Move 'balance' HAProxy keyword

    The "balance" keyword is not valid in a frontend section. From the
    HAProxy documentation[1]:

    balance <algorithm> [ <arguments> ]
    balance url_param <param> [check_post [<max_wait>]]
      Define the load balancing algorithm to be used in a backend.
      May be used in sections : defaults | frontend | listen | backend
                                     yes | no | yes | yes

    When running HAProxy using the "split" template style, where a
    frontend/backend pair are used instead of one listen section, HAProxy
    will emit warnings for the Horizon config due to this.

    [1]: https://www.haproxy.org/download/1.5/doc/configuration.txt

    Closes-Bug: #1872540
    Change-Id: I91cee275d91a51944298618493f4ea0cd80282cc
    (cherry picked from commit 5c760df3d5f1886290b8dd86eb515acc06e66c9a)