Docker app server ip address 127.0.0.1 difference of 0.0.0.0 ip

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You must set a container’s main process to bind to the special 0.0.0.0 “all interfaces” address, or it will be unreachable from outside the container.

In Docker 127.0.0.1 almost always means “this container”, not “this machine”. If you make an outbound connection to 127.0.0.1 from a container it will return to the same container; if you bind a server to 127.0.0.1 it will not accept connections from outside.

One of the core things Docker does is to give each container its own separate network space. In particular, each container has its own lo interface and its own notion of localhost.

At a very low level, network services call the bind(2) system call to start accepting connections. That takes an address parameter. It can be one of two things: either it can be the IP address of some system interface, or it can be the special 0.0.0.0 “all interfaces” address. If you pick an interface, it will only accept connections from that interface; if you have two network cards on a physical system, for example, you can use this to only accept connections from one network but not the other.

So, if you set a service to bind to 127.0.0.1, that’s the address of the lo interface, and the service will only accept connections from that interface. But each container has its own lo interface and its own localhost, so this setting causes the service to refuse connections unless they’re initiated from within the container itself. It you set it to bind to 0.0.0.0, it will also accept connections from the per-container eth0 interface, where all connections from outside the container arrive.

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