runner

#!/bin/bash
#
# runner
#
# Starts a Docker container from a CouchDb service definition
#
set -u

function error
{
  echo "error: $1" >&2
  exit 1
}

function stop
{
  local service_address="$1"
  local container_ip="$2"
  local container_port="$3"

  trap '' EXIT TERM INT # ignore signals

  ipvsadm -d -t "$service_address" -r "${container_ip}:${container_port}"

  systemd-notify STOPPING=1 STATUS="Stopping containers"
  sleep 5

  echo "[stopping container]"
  docker stop "$container_id"
}

function wait_for_tcp
{
  local ip="$1"
  local port="$2"
  echo "[waiting for health check tcp://$ip:$port]"

  for ((i = 0; i <= 500; i++))
  do
    ncat -z "$ip" "$port"
    if [ "$?" -eq 0 ]
    then
      return 0
    fi
    sleep 1
  done

  error "Container health check failed"
}

function wait_for_http
{
  local ip="$1"
  local port="$2"
  echo "[waiting for health check http://$ip:$port]"

  curl --fail --silent \
       --retry-max-time 500 \
       --retry-delay 1 \
       --retry-connrefused \
       --retry 600 \
       "http://${ip}:${port}/"
  [ "$?" -eq 0 ] || error "Container health check failed"
}

function main
{
  local service_name="$1"
  local service_instance="$2"
  local service_address="$3"

  config=$(curl -sf "${COUCHDB_URL}/${service_name}?rev=${service_instance}")
  [ "$?" -eq 0 ] || error "Failed fetch config document"

  set -e
  container_name="${service_name}.${service_instance}"
  container_image=$(jq -r '.image' <<< "$config")
  container_port=$(jq -r '.port' <<< "$config")

  args=(
    '--detach'
    '--log-driver' 'journald'
    '--name' "$container_name"
    '--label' "service_name=$service_name"
    '-p' "$container_port"
    '-e' "SYSTEM_HOSTNAME=$(hostname)"
  )

  while read arg; do args+=("-e" "$arg"); done < \
    <(jq -r '.environment // {} | to_entries[] | .key + "=" + .value' <<< "$config")

  while read arg; do args+=("-v" "$arg"); done < \
    <(jq -r '.volumes // [] | .[]' <<< "$config")

  args+=("$container_image")

  set +e

  # Remove previous container
  if [ "$(docker ps -aq -f status=exited -f name=$container_name)" ]
  then
    echo "[removing exited container]"
    docker rm "$container_name"
  fi

  # Start container
  echo "[starting container]"
  container_id=$(docker run "${args[@]}")
  [ "$?" -eq 0 ] || error "Failed to launch container"

  # Find container IP address
  container_ip=$(docker inspect "$container_id" | jq -r '.[0].NetworkSettings.IPAddress')

  # Health check
  jq -e '.health_check == "tcp"' > /dev/null <<< "$config" && \
      wait_for_tcp "$container_ip" "$container_port" || \
      wait_for_http "$container_ip" "$container_port"

  # Add to load balancer
  ipvsadm -a -t "$service_address" -r "${container_ip}:${container_port}" -m

  systemd-notify READY=1 STATUS="Up and running"

  # Setup shutdown hooks
  trap "stop $service_address $container_ip $container_port" EXIT TERM INT

  echo "[waiting for container to exit]"
  docker wait "$container_id"

  # Get the exit code and exit
  rc=$(docker inspect --format '{{.State.ExitCode}}' $container_id)
  echo "[container exited with status code $rc]"
  exit 0
}

(( $# != 3 )) && error "usage: $0 service-name service-instance service-address"
main "$1" "$2" "$3"