If somebody wants to accomplish the same thing, I solved it using a start script to run dagit and daemon in one container.
The sleep is necessary, because otherwhise there will be a occasional error during startup. (alembic_version error)
You can search for that error here in slack.
dagit -h 0.0.0.0 -p 3000 &
sleep 10 &&
dagster-daemon run &
wait -n
exit $?