After a reboot of a container, I noticed the port mappings changed.
A quick edit of:
root@synonas:/usr/syno/etc/packages/Docker# cat ora12c001.config {"cap_add":[],"cap_drop":[],"cmd":"","cpu_priority":0,"ddsm_bind_share":"","devices":[],"enable_publish_all_ports":false,"enable_restart_policy":false,"enabled":true,"env_variables":[],"exportin g":false,"id":"fe1a6706865e0a7eaf735a8d17530b23805b5291aa4749424eac30dc459f1a63","image":"sath89/oracle-12c:latest","is_ddsm":false,"is_package":false,"links":[],"memory_limit":0,"name":"ora12c001","network":[{"driver":"","name":"bridge"}],"port_bindings":[{"container_port":1521,"fixed":false,"host_port":0,"type":"tcp"},{"container_port":8080,"fixed":false,"host_port":0,"type":"tcp"}],
put a stop to that.
Just put the desired value in place of the 0 in the “port_binding” section.