wrapper script to launch command when dependency is ready

wait-until-ready.sh

#!/bin/sh

readonly MAX_RETRY=10
readonly DELAY_BETWEEN_TRY_IN_SECONDS=10
readonly DEPENDENCY_CHECK_COMMAND=$1
readonly CONTAINER_RUN_COMMAND=$2

# wait until a command succeeds
#
# Usage: waitUntilReady "<command arg1...argN>"
function waitUntilReady() {
  local count=0
  local command=$1

  while ! eval ${command}; do
    count=$((${count} + 1))
    if [[ ${count} -lt ${MAX_RETRY} ]]; then
      echo "INFO - not ready, waiting ${DELAY_BETWEEN_TRY_IN_SECONDS} seconds (${count}/${MAX_RETRY})..."
      sleep ${DELAY_BETWEEN_TRY_IN_SECONDS}
    else
      echo "ERROR - not ready, no more retries left."
      return 1
    fi
  done

  echo "INFO - ready!"
  return 0
}

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 <DEPENDENCY_CHECK_COMMAND> <CONTAINER_RUN_COMMAND>" >&2
  exit 1
fi

echo "INFO - checking dependency status"
if ! waitUntilReady "${DEPENDENCY_CHECK_COMMAND}"; then
  echo "ERROR - dependency not ready, stopping container"
  exit 2
fi

echo "INFO - starting container"
${CONTAINER_RUN_COMMAND}

DB dependency:

ENV HEALTH_CHECK_COMMAND "curl --max-time 5 --silent --show-error --fail http://foo/bar/health"
ENV CONTAINER_RUN_COMMAND "my-command.sh"
ENTRYPOINT /bin/bash wait-until-ready.sh "${HEALTH_CHECK_COMMAND}" "${CONTAINER_RUN_COMMAND}"

Server dependency:

ENV HEALTH_CHECK_COMMAND "mysql -h dbhost -u dbuser -pdbpassword -D dbname -e 'SELECT 1'"
ENV CONTAINER_RUN_COMMAND "start-server.sh"
ENTRYPOINT /bin/bash wait-until-ready.sh "${HEALTH_CHECK_COMMAND}" "${CONTAINER_RUN_COMMAND}"