Gfilui

I have docker up and running, with the docker-provided CE variant:

# dpkg -l '*docker*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===================================================-==============================-==============================-===========================================================================================================
un docker <none> <none> (no description available)
ii docker-ce 18.03.0~ce-0~ubuntu amd64 Docker: the open-source application container engine
un docker-ee <none> <none> (no description available)
rc docker-engine 17.05.0~ce-0~ubuntu-xenial amd64 Docker: the open-source application container engine
un docker-engine-cs <none> <none> (no description available)
un docker.io <none> <none> (no description available)

I'm doing basic system house-keeping and see that the older docker-engine has some config files still present. I thought to do a simple apt-get purge docker-engine, but thought I'd look into what would happen. The /var/lib/dpkg/info/docker-engine.list just contains:

/etc
/etc/init.d
/etc/default
/etc/init

so I'm not worried that purging would harm the current docker-ce package, but the .postrm file does a bit more. In if blocks specifically limited to "purge" operations, I see:

update-rc.d docker remove >/dev/null
deb-systemd-helper purge docker.service docker.socket >/dev/null
deb-systemd-helper unmask docker.service docker.socket >/dev/null

which do not (to me) immediately differentiate between the two packages. The first command looks for /etc/init.d/docker which, at this point, is the one installed by docker-ce, so I wonder if executing that command would close down the wrong service.

I can recover from a simple "service was disabled", but I don't know what else will be happening to know if apt-get purge docker-engine would further disrupt my current happily-working docker-ce instance.

If my concern is correct (that purging one will adversely affect the other), then is there a safer way to clean this up? I do not mind removing files manually, if that will suffice. My sole goal is to not endanger my current docker instance, as it feeds my company's docker swarm manager, on which I have a lot riding.