Start a Docker container with IP addr deducted from hostname & DNS

docker-start.sh

#!/bin/bash

# Author:  Fulup Ar Foll  (iot.bzh)
# Date:    July-2015
# Oject:   Start a Docker container with IP addr deducted from hostname & DNS
# Syntax:  docker-start [brige=br0] [subnet=10.20.1.0] [netmask=24] [addr=auto] [gateway=auto] containerName/ID
# Licence: Any OpenSource Licences you like, until you fix bugs by yourself :)

# Source:     https://gist.github.com/fulup-bzh
# Reference:  http://blog.oddbit.com/2014/08/11/four-ways-to-connect-a-docker

# Default Values
# ----------------
  BRIDGE=br0
  NETMASK=24
  SUBNET=10.20.1.0  

# Check if argument exist
# --------------------------
OPTCOUNT=0
CheckArg() {
  cmd=$(echo $1 | cut -f1 -d=)
  val=$(echo $1 | cut -f2 -d=)
  OPTCOUNT=`expr $OPTCOUNT + 1`

  if test "$val" != "auto"; then
    case "$cmd" in
    bridge)   BRIDGE="$val"  ;;
    addr)     CADDR="$val"   ;;
    gateway)  GATEWAY="$val" ;;
    subnet)   SUBNET="$val"  ;;
    netmask)  NETMASK="$val" ;;
	   
    *) 
      echo "Error: $cmd=xxxx unknown option"
      exit 1
      ;;
    esac
  fi
}

# Parse CLI arguments
# -------------------
EvalArgs() {
  for arg in "$@"
  do
    if expr 'index' "$arg" '=' '>' '1' >/dev/null
    then
        CheckArg "${arg}"
    fi
  done
}

# Extract command line Argument
EvalArgs "$@"

# Conainer name is cli's last argement
shift $OPTCOUNT; CNAME=$1
if test -z "$CNAME"; then
  echo "Syntaxe: docker-start [bridge=xx] [addr=x.x.x.x] [gateway=x.x.x.x] [subnet=x.x.x.0] [netmask=xx] MyContainerID/Name"
  exit
fi
 
ip link show "$BRIDGE" >/dev/null
if test $? -ne 0
then
   echo "Error: bridge="$BRIDGE" does not exist"
   exit 1
fi


if test -z "$GATEWAY"; then
    GATEWAY=`ip route show 0.0.0.0/0 dev $BRIDGE | awk '{print $3}'`
    if test -z "$GATEWAY"; then
      GATEWAY=`ip route show  "$SUBNET/$NETMASK" dev $BRIDGE | awk '{print $7}'`
    fi
fi

if test -z "$GATEWAY"; then
  echo "Hoops no default gateway for $BRIDGE"
  exit
fi

# check container exist and is stopped
  DOCKID=`docker ps -a | grep $CNAME`
  if test -z "$DOCKID"; then 
    echo "Hoops: container=[$CNAME] not found => docker ps -a"
    exit
  fi

# if no IP provided get one from DNS lookup
if test -z "$CADDR"; then
  CADDR=`getent hosts $CNAME | awk '{print $1}'`
  if test -z "$CADDR"; then
    echo "Hoops: host=$CNAME no IP found =>  docker-start.sh $CNAME x.x.x.x"
    exit
  fi
fi

echo "start docker container name=$CNAME addr=$CADDR/$NETMASK"
# docker run  --detach=true --net=none --hostname=$CNAME --name=$CNAME --privileged  -i -t centos:latest /lib/systemd/systemd

# if container is stopped let's start it now
DOCKSTOP=`docker ps --filter "status=exited" | grep $CNAME`
if test ! -z "$DOCKSTOP"; then 
  docker start $CNAME >/dev/null
fi

# get container namespace PID
CPID=`docker inspect --format {{.State.Pid}} $CNAME`  # get container namespace PID
if test -z "$CPID"; then
   echo "Hoops: failled to start container=[$CNAME]"
   exit
fi

# if root ssh auth does not exist buit one from hypervisor
sudo test -f  /root/.ssh/authorized_keys
if test $? -eq 0; then
  sudo nsenter -t $CPID --mount ls /root/.ssh/authorized_keys >/dev/null 2>/dev/null
  if test $? -ne 0; then
    echo "Setting container initial /root/.ssh/authorized_keys"
    sudo nsenter -t $CPID --mount mkdir -p /root/.ssh 2>/dev/null
    sudo cat /root/.ssh/authorized_keys | sudo nsenter -t $CPID --mount tee /root/.ssh/authorized_keys >/dev/null
  fi
fi

 # make sure CNAME is not to long for an network interface name
 CNETNAME=${CNAME:0:8}-veth0

 sudo ip link add veth0 type veth peer name $CNETNAME       # create a new interface on hypervisor
 sudo ip link set $CNETNAME  up                             # activate newly create interface on host
 sudo brctl addif $BRIDGE $CNETNAME                         # add new interface to the bridge
 sudo ip link set netns $CPID dev veth0                     # move veth0 interface into container name space
 sudo nsenter -t $CPID --net ip link set veth0 up           # up veth0 within container
 sudo nsenter -t $CPID --net ip addr add  $CADDR/$NETMASK dev veth0     # set IP addr within container
 sudo nsenter -t $CPID --net ip route add default via $GATEWAY dev veth0

echo "enter container => docker exec -it $CNAME bash"

ping -W 10 -c 1 10.20.1.132 >/dev/null
if test $? -ne 0; then
   echo "Hoops ping FAIL"
else 
   echo "OK: ping respond"
fi