I followed https://docs.mattermost.com/install/prod-docker.html to install MM on VPS running discourse alreaday but run into
root@Ubuntu18:~/mattermost-docker# docker-compose up -d
Creating network "mattermost-docker_default" with the default driver
Creating mattermost-docker_app_1 ...
Creating mattermost-docker_web_1 ... error
Creating mattermost-docker_db_1  ...
Creating mattermost-docker_app_1 ... done
ERROR: for mattermost-docker_web_1  Cannot start service web: driver failed programming external connectivity on endpoint mattermost-docker_web_1 (a210daeda9eb7f3df79c1d8e2be141f8a3fbc9c4cae8ffcb305d0fdab5a1f630): Bind for 0.0.0.0:443 faCreating mattermost-docker_db_1  ... done
ERROR: for web  Cannot start service web: driver failed programming external connectivity on endpoint mattermost-docker_web_1 (a210daeda9eb7f3df79c1d8e2be141f8a3fbc9c4cae8ffcb305d0fdab5a1f630): Bind for 0.0.0.0:443 failed: port is already allocated
ERROR: Encountered errors while bringing up the project.
so I did
root@Ubuntu18:~/mattermost-docker#  sudo lsof -i -P -n | grep LISTEN
sshd        959            root    3u  IPv4   18822      0t0  TCP *:22 (LISTEN)
sshd        959            root    4u  IPv6   18829      0t0  TCP *:22 (LISTEN)
docker-pr  1688            root    4u  IPv6 3748819      0t0  TCP *:443 (LISTEN)
docker-pr  1699            root    4u  IPv6 3748846      0t0  TCP *:80 (LISTEN)
systemd-r  8636 systemd-resolve   13u  IPv4 3181490      0t0  TCP 127.0.0.53:53 (LISTEN)
and
root@Ubuntu18:~/mattermost-docker# docker ps
CONTAINER ID        IMAGE                   COMMAND                  CREATED             STATUS                   PORTS                                      NAMES
0148a95a2c09        mattermost-docker_db    "/entrypoint.sh post…"   6 minutes ago       Up 6 minutes (healthy)   5432/tcp                                   mattermost-docker_db_1
4ec918f2efa8        mattermost-docker_app   "/entrypoint.sh matt…"   6 minutes ago       Up 6 minutes (healthy)   8000/tcp                                   mattermost-docker_app_1
c447e7f705b5        local_discourse/app     "/sbin/boot"             3 weeks ago         Up 3 weeks               0.0.0.0:80->80/tcp, 0.0.0.0:443->443/tcp   app
telling me that discourse is already using 443.
So the solution is a proxy but somewhere in the docs, it was mentioned that SSO is incompatible with running behind a proxy. Is that still true or any other side effects of running behind a proxy?
I cannot find anything anymore.
Instead, I find good tutorials explaining how to run behind a proxy.
https://docs.mattermost.com/install/config-proxy-nginx.html
…/outbound-proxy.html
I’m supposed to do this changes before doing  ~/mattermost-docker# docker-compose up -d?