`redis-server` installation fails when IPv6 is disabled

[907th]

I used this Redis role after OS hardening role which disabled all IPv6 settings in sysctl.conf. That resulted in the failure of apt-get install redis-server (I'm on Ubuntu server) command.

Error output is:

Reading package lists...
Building dependency tree...
Reading state information...
redis-server is already the newest version (5:4.0.9-1ubuntu0.1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up redis-server (5:4.0.9-1ubuntu0.1) ...
Job for redis-server.service failed because a timeout was exceeded.
See \"systemctl status redis-server.service\" and \"journalctl -xe\" for details.
invoke-rc.d: initscript redis-server, action \"start\" failed.
* redis-server.service - Advanced key-value store
   Loaded: loaded (/lib/systemd/system/redis-server.service; disabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: timeout) since Wed 2019-01-30 15:26:36 MSK; 7ms ago
     Docs: http://redis.io/documentation,
           man:redis-server(1)

Jan 30 15:26:36 eps-lw-banking systemd[1]: \u001b[0;1;31m\u001b[0;1;39m\u001b[0;1;31mFailed to start Advanced key-value store.\u001b[0m
dpkg: error processing package redis-server (--configure):
 installed redis-server package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 redis-server

The problem is that default redis.conf from redis-server package contains bind 127.0.0.1 ::1 line, so Redis tries to bind on disabled IPv6 address and hangs.

I found discussions of this problem on Ubuntu and Debian bugtrackers. I understand that this is more redis-server package problem than the problem of this role, but it would be great if this role had a workaround for this situation.

By default, this role is configured to set bind to 127.0.0.1 (redis_bind_interface setting), so I found the following solution: I changed the order of Redis configuration and Redis installation tasks in the play, and I also added the task for creating the /etc/redis dir:

- name: Ensure Redis configuration dir exists.
  file:
    path: "{{ redis_conf_path | dirname }}"
    state: directory
    mode: 0755

- name: Ensure Redis is configured.
  template:
    src: redis.conf.j2
    dest: "{{ redis_conf_path }}"
    mode: 0644
  notify: restart redis

# Setup/install tasks.
- include_tasks: setup-Debian.yml
  when: ansible_os_family == 'Debian'

Now, when redis-server installation happens, the installer uses preconfigured redis.conf and all works even if IPv6 is totally disabled.

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