docker-ns

#!/bin/bash

# this borrows from https://github.com/jpetazzo/pipework

set -e

GUESTNAME=$1
shift 1

[ "$GUESTNAME" ] || {
    echo "Syntax:"
    echo "docker-ns <guest> <command> <arg> ..."
    exit 1
}

DOCKERPID=$(docker inspect --format='{{ .State.Pid }}' $GUESTNAME)
[ "$DOCKERPID" = 0 ] && {
    echo "Docker inspect returned invalid PID 0"
    exit 1
}
[ "$DOCKERPID" = "<no value>" ] && {
    echo "Container $GUESTNAME unknown to Docker."
    exit 1
}

NSPID=$DOCKERPID

[ ! -d /var/run/netns ] && mkdir -p /var/run/netns
[ -f /var/run/netns/$NSPID ] && rm -f /var/run/netns/$NSPID
ln -s /proc/$NSPID/ns/net /var/run/netns/$NSPID

ip netns exec $NSPID "$@"

[ -f /var/run/netns/$NSPID ] && rm -f /var/run/netns/$NSPID

exit 0