Test ansible playbook using rpm-based distros with systemd as Docker containers - travis-ci

Question

I am writing ansible playbook for the Ansible.Galaxy that will install nginx on any Linux distros.
But I felt to test it with Travis CI and Docker on images that include Systemd. Because SystemD gives an error:
Failed to get D-Bus connection: No connection to service manager.
As you can see https://travis-ci.org/weldpua2008/ansible-nginx/jobs/78864352
There were errors.
So I try to represent it:
~# git clone https://github.com/weldpua2008/ansible-nginx.git
~# cd ansible-nginx
~# docker run -ti --rm=true -v `pwd`:/ansible-nginx:rw centos:7 /bin/bash ^C
~# cd ansible-nginx/
~/ansible-nginx# docker run -ti --rm=true -v `pwd`:/ansible-nginx:rw centos:7 /bin/bash
[root#2f6955a46b42 /]# /ansible-nginx/tests/test-on-rpm.sh
TASK: [ansible-nginx | create document root directory if needed] **************
ok: [localhost]
TASK: [ansible-nginx | Starting nginx service] ********************************
failed: [localhost] => {"failed": true}
msg: no service or tool found for: nginx
FATAL: all hosts have already failed -- aborting
PLAY RECAP ********************************************************************
to retry, use: --limit #/root/test.retry
localhost : ok=5 changed=2 unreachable=0 failed=1
Maybe there isn't this service?
[root#2f6955a46b42 /]# systemctl enable nginx.service
[root#2f6955a46b42 /]# systemctl -t service -a
Failed to get D-Bus connection: No connection to service manager.
[root#2f6955a46b42 /]# chkconfig --list
Note: This output shows SysV services only and does not include native
systemd services. SysV configuration data might be overridden by native
systemd configuration.
If you want to list systemd services use 'systemctl list-unit-files'.
To see services enabled on particular target use
'systemctl list-dependencies [target]'.
It's how I try to start service in ansible: https://github.com/weldpua2008/ansible-nginx/blob/master/tasks/main-centos.yml#L24
- name: Starting nginx service
service: name=nginx state=started
tags:
- nginx
I tied to solve with https://github.com/docker/docker/issues/7459

Answer 1

This is caused by the fact that Docker (normal "unprivileged") containers don't have the permissions to run systemd (as it wants access to the /sys/fs/cgroup filesystem).
But this is really because Docker containers prefer to run one process, the process you are trying to use them for - think of them as "a Unix process with a bunch of supporting utilities", rather than as "mini-VMs".
You need a simple Dockerfile inheriting from the Centos one, which installs nginx and then has a final CMD as something like:
CMD /usr/sbin/nginx -g "daemon off;"
For tips, here's the official nginx Dockerfile https://github.com/nginxinc/docker-nginx/blob/7f3ef0927ec619d20181e677c97f991df0d7d446/Dockerfile