system-helpers/usr/local/bin/docker_check

#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: docker_check [CONFIG_FILE (absolute path)]

If no CONFIG_FILE is given, HOME/.docker_check.conf or /etc/docker_check.conf is used. This fallback option
has to exist or the script will exit.

Configuration can be done in any file and any pre-defined variable can be overwritten.

The following are optional or have reasonable defaults:
DOCKER_CHECK_LIST_FILE="HOME/.docker_check.list" // the list file (output current running to file: docker ps --format '{{.Names}}' >> $HOME/.docker_check.list)
DOCKER_CHECK_NOTIFY_LEVELS=("UNKNOWN" "WARNING" "CRITICAL") // when to notify/output/send mail. possible: "UNKNOWN" "WARNING" "CRITICAL" "INFO", should at least be ()
DOCKER_CHECK_MAIL_ENABLED=false // send email (address has to be set), values: false|true
DOCKER_CHECK_MAIL_ADDRESS="" // mail.rc has to be configured

You can copy this script to '/usr/local/bin' and use create a custom CONFIG_FILE as user. Examples can be found in '/usr/share/doc/<scriptname>'.
EOF
)
	echo "$USAGE";
}

set -e;

HOSTNAME=$(hostname)
DOCKER_CHECK_LIST_FILE="$HOME/.docker_check.list"
DOCKER_CHECK_GLOBAL_LIST_FILE="/etc/docker_check.list"
DOCKER_CHECK_NOTIFY_LEVELS=("UNKNOWN" "WARNING" "CRITICAL")
DOCKER_CHECK_MAIL_ENABLED=false
DOCKER_CHECK_MAIL_ADDRESS=""
CONTAINERS=()

# check for config file
apply_config() {
  local config=$1;

  if [[ ! -f "$config" ]]; then
      echo "No config file specified";
      echo "";
      usage;
      exit 1;
  fi

  set -a;
  # shellcheck disable=SC1090
  source "$config";
  set +a;
}

source_config() {
  local config=$1;
  local configFallback=$2;
  local configGlobalFallback=$3;

  if [[ -f "$config" ]]; then
    apply_config "$config";
    return;
  fi

  if [[ -f "$configFallback" ]]; then
    apply_config "$configFallback";
    return;
  fi

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}
source_config "$1" "$HOME/.docker_check.conf" "/etc/docker_check.conf"

listFileToUse=""
if [[ -f "$DOCKER_CHECK_LIST_FILE" ]]; then
	listFileToUse="$DOCKER_CHECK_LIST_FILE"
else
	listFileToUse="$DOCKER_CHECK_GLOBAL_LIST_FILE"
fi

if [[ ! -f $listFileToUse ]]; then
	echo "$listFileToUse doesn't exist. Add a file which holds one systemd service or timer per line.";
	echo "";
	usage;
	exit 1;
fi

echo "Scanning $listFileToUse for containers...";
while IFS='' read -r line || [[ -n "$line" ]]; do
    CONTAINERS+=("$line")
	echo "-> Found $line";
done < "$listFileToUse"

# check if current status is in array of DOCKER_CHECK_NOTIFY_LEVELS
function shouldLog() {
	local VALUE=$1;

	for i in "${DOCKER_CHECK_NOTIFY_LEVELS[@]}"; do
	    if [ "$i" == "$VALUE" ] ; then
	        echo true;
	        return;
	    fi
	done

	echo false;
}

# log and send mail if enabled
function log() {
	local CONTAINER=$1;
	local STATUS=$2;
	local MESSAGE=$3;

	# shellcheck disable=SC2155
	local SHOULD_LOG=$(shouldLog "$STATUS");
	if [ "$SHOULD_LOG" = "true" ]; then
		local SUBJECT="[docker $HOSTNAME] $STATUS $CONTAINER";
		echo "$SUBJECT: $MESSAGE";

		if [ "$DOCKER_CHECK_MAIL_ENABLED" = true ]; then
	        echo "$MESSAGE"|mailx -Ssendwait -s "$SUBJECT" "$DOCKER_CHECK_MAIL_ADDRESS";
	    fi
	fi
}

# get status for a docker container
function checkContainer() {
	local CONTAINER=$1;

	# shellcheck disable=SC2268
	if [ "x${CONTAINER}" == "x" ]; then
  		log "$CONTAINER" "UNKNOWN" "Container ID or Friendly Name Required"
  		return;
	fi

	# shellcheck disable=SC2268
	if [ "x$(which docker)" == "x" ]; then
		log "$CONTAINER" "UNKNOWN" "Missing docker binary"
		return;
	fi

	docker info > /dev/null 2>&1
	# shellcheck disable=SC2181
	if [ $? -ne 0 ]; then
		log "$CONTAINER" "UNKNOWN" "Unable to talk to the docker daemon"
		return;
	fi

	RUNNING=$(docker inspect --format="{{.State.Running}}" "$CONTAINER" 2> /dev/null)

	if [ $? -eq 1 ]; then
		log "${CONTAINER}" "UNKNOWN" "$CONTAINER does not exist."
		return;
	fi

	if [ "$RUNNING" == "false" ]; then
		log "${CONTAINER}" "CRITICAL" "$CONTAINER is not running."
		return;
	fi

	RESTARTING=$(docker inspect --format="{{.State.Restarting}}" "$CONTAINER")

	if [ "$RESTARTING" == "true" ]; then
		log "$CONTAINER" "WARNING" "$CONTAINER state is restarting."
		return;
	fi

	#STARTED=$(docker inspect --format="{{.State.StartedAt}}" $CONTAINER)
	#NETWORK=$(docker inspect --format="{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}" $CONTAINER)
	#log "$CONTAINER" "INFO" "$CONTAINER is running. IP: $NETWORK, StartedAt: $STARTED"
	
	log "$CONTAINER" "INFO" "$CONTAINER is running."

	return;
}

# execute check for defined containers
for container in "${CONTAINERS[@]}"; do
	echo "Checking $container...";
	checkContainer "$container"
done