USER directive in images

Issue

• What is the USER which should be used in OSE3 ?
• In some dockerfiles examples we can see that the "USER 1001" is used. Could you please explain which user it is (maybe a default one, is it created by OSE3 when running the image) ... ) ?
• Do you know how the UID are allocated to the Linux users ? maybe the first one allocated to a new created user is 1001, or something else ? Are there some preset users in the system (I only know that root is UDI=0) ?
  • If a OSE3 user does not define a USER directive in his Dockerfile image, then the containers running this image will need to run as root ? And by default, running images as root is not allowed in OSE3, unless we relax the security constraints ?