docker-compose referencing wrong ports - docker

Question

I am running multiple docker-compositions on one host (identical images for different usecases).
For that reason I use different HTTPS (+REST) ports the compositions are available remotely under. However, docker will reference the port range of the first composition in every other composition as well, but not use it. Although I cannot see any negative implication atm, I would like to get rid of it, fearing that some implication might eventually arise.
docker ps shows this
PORTS
Second container:
**8643-8644/tcp**, 0.0.0.0:8743-8744->8743-8744/tcp
0.0.0.0:27020->27020/tcp
First container:
0.0.0.0:**8643-8644->8643-8644**/tcp
0.0.0.0:27019->27019/tcp
First docker-compose file (excerpt):
version: '2'
services:
mongo:
image: *****
ports:
- "27019:27019"
tty: true
volumes:
- /data/mongodb
- /data/db
- /var/log/mongodb
entrypoint: [ "/usr/bin/mongod", "--port", "27019" ]
rom:
image: *****
links:
- mongo
ports:
- "8643:8643"
- "8644:8644"
environment:
WEB_PORT_SECURE: 8643
REST_PORT_SECURE: 8644
MONGO_PORT: 27019
MONGO_INST: mongod
entrypoint: [ "node", "/usr/src/app/app.js" ]
Second docker-compose file (excerpt):
version: '2'
services:
mongo:
image: *****
ports:
- "27020:27020"
tty: true
volumes:
- /data/mongodb
- /data/db
- /var/log/mongodb
entrypoint: [ "/usr/bin/mongod", "--port", "27020" ]
rom:
image: *****
links:
- mongo
ports:
- "8743:8743"
- "8744:8744"
environment:
WEB_PORT_SECURE: 8743
REST_PORT_SECURE: 8744
MONGO_PORT: 27020
MONGO_INST: mongod
entrypoint: [ "node", "/usr/src/app/app.js" ]
and finally, docker inspect shows this for the second container
"Config": {
"Hostname": *****,
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"8643/tcp": {},
"8644/tcp": {},
"8743/tcp": {},
"8744/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"MONGO_PORT=27020",
"MONGO_INST=mongodb",
"WEB_PORT_SECURE=8743",
"REST_PORT_SECURE=8744",
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"NPM_CONFIG_LOGLEVEL=info",
"NODE_VERSION=4.7.2",
"WORK_DIR=/usr/src/app"
],
"NetworkSettings": {
"Ports": {
"8643/tcp": null,
"8644/tcp": null,
"8743/tcp": [
{
"HostIp": "0.0.0.0",
"HostPort": "8743"
}
],
"8744/tcp": [
{
"HostIp": "0.0.0.0",
"HostPort": "8744"
}
]
},
The last block clearly shows that docker is not doing anything with the 8643 and 8644 port, but still references it there.
"8643/tcp": null,
"8644/tcp": null,
Any idea why this happens and how to avoid it?

Answer 1

They are there because the image exposes them (built with EXPOSE).
This is not a problem, it's totally normal. You won't have a problem unless you try to export the same port on the outside host more than once. Here, none of your exported ports are in conflict.
0.0.0.0:8743-8744->8743-8744/tcp
0.0.0.0:27020->27020/tcp
0.0.0.0:8643-8644->8643-8644/tcp
0.0.0.0:27019->27019/tcp
You are exporting 8643-8644, 8743-8744, 27019, 27020. No conflicts.
A container can expose whatever ports it wants, it is only important that exposed ports are not in conflict with one another.