PortAllocator redesign

[mavenugo]

Port Allocator is supposed to be a reflection of the Operating System construct and must be in sync with OS view of the allocated ports.

The current port allocator reflects the software db of that construct.
Also, port allocator must also provide allocation for individual network namespace and not just for the global space.

[ghost]

In case host OS does a change in the port allocation which might affect the underlying containers what is the workflow? Docker daemon monitors such changes and via libnetwork will inform the underlying containers or ?

[akerouanton]

With the recent changes made in Docker v27.0, libnetwork now bind sockets before inserting iptables rules. That way, libnetwork alone doesn't determine whether a port is free.

Although the PortAllocator wasn't redesigned (it's still used to iterate on known-bound ports), I think that covers what this ticket was up for.