networking - What does the 0.0.0.0 in front of ports mean in a docker-compose.yml?

Question

I made an image for the vsftpd daemon, which is a ftp service. I naively came up with the following docker-compose.yml :

version: '3'

services:
        ftps:
                image: vsftpd
                ports:
                        - 21:21
                        - 21000-21010:21000-21010

I had to change the 21:21 part to 0.0.0.0:21:21 (following files I found on Github). What I do not understand is why it works as it is (even file transfer), even though I did not prefix the other ports (21000 to 21010) with 0.0.0.0.

Answer 1

等待大神答复