A service script that waits on "docker events" and adds new containers and their host names to "dnsmasq"

auto-dev-hosts

#!/bin/bash
# put me in /usr/bin/auto-dev-hosts

HOSTSDIR=/tmp/auto-dev-hosts
# create dir
install -d "$HOSTSDIR"

RELOADFLAG=/tmp/auto-dev-hosts.flag
SCRIPTNAME=$(basename "$0")

function add_hosts {
  for CONTAINER in "$@"
  do
    # write temporary hosts file
    docker inspect -f '{{$c := .Config}}{{range .NetworkSettings.Networks}}{{if .IPAddress}}{{.IPAddress}}{{if $d := $c.Domainname}}	{{$c.Hostname}}.{{$d}}{{end}}	{{$c.Hostname}}{{end}}{{end}}' "$CONTAINER" > $HOSTSDIR/$CONTAINER
  done
}

# reload dnsmasq if root
# delay for 3 seconds in case there are more edits coming
function reload_dnsmasq {
  if (( EUID == 0 ))
  then
    (
      sleep 3
      if [[ -f $RELOADFLAG ]]
      then
        echo "Reloading dnsmasq..."
        pkill -x -1 dnsmasq
      fi
      rm -f $RELOADFLAG
    )&

    touch $RELOADFLAG
  fi
}

function clean_up {
  FILES=$(shopt -s nullglob; echo ${HOSTSDIR}/*)
  if (( ${#FILES} ))
  then
    rm "${FILES[@]}"
    reload_dnsmasq
  fi
  rmdir "$HOSTSDIR"
  exit
}

trap clean_up SIGHUP SIGINT SIGTERM

RUNNING=($(docker ps -q --no-trunc))
if (( ${#RUNNING} ))
then
  docker inspect -f '{{.Name}} was found at{{range .NetworkSettings.Networks}} {{.IPAddress}}{{end}}' "${RUNNING[@]}"
  add_hosts "${RUNNING[@]}"
  reload_dnsmasq
fi

docker events -f "type=container" -f "event=start" -f "event=stop" -f "event=die" | while read -a line
do
  EVENT=${line[2]}
  CONTAINER=${line[3]}

  case $EVENT in
  start)
    docker inspect -f '{{$Name := .Name}}{{range .NetworkSettings.Networks}}{{$Name}} has started at {{.IPAddress}}{{end}}' "$CONTAINER"
    add_hosts "$CONTAINER"
    reload_dnsmasq
    ;;
  stop|die)
    docker inspect -f '{{.Name}} has stopped.' "$CONTAINER"
    if [[ -s "$HOSTSDIR/$CONTAINER" ]]
    then
      rm "$HOSTSDIR/$CONTAINER"
      reload_dnsmasq
    else
      rm -f "$HOSTSDIR/$CONTAINER"
    fi
    ;;
  esac
done

clean_up

auto-dev-hosts.dnsmasq.d

# put me in /etc/NetworkManager/dnsmasq.d/auto-dev-hosts
hostsdir=/tmp/auto-dev-hosts