Java app Docker entrypoint script, with a simple JVM flags file

docker-entrypoint.sh

#!/bin/bash

# Contains a few particularities of $DAYJOB's infra environment, but you get the, erm, gist.
set -o errexit

declare -r app_jar=/opt/myapp/my-app.jar
declare -r consul_template_config=/etc/consul.d/template/config.json
declare -r flags_file="${JVM_FLAGS_FILE:=/etc/myapp/application.ini}"

# For JMX's weird connection negotiation in a container world
declare rmi_hostname=$(hostname)

notice() {
  echo "[my-app] $*"
}

# Loads a configuration file containing base command line options for this script.
# Strips comment lines beginning with pound sign.
#
# Idea stolen from sbt-native-packager, eases making and reviewing changes to
# numerous JVM flags, etc.
loadConfigFile() {
  sed $'/^\#/d;/^$/d;s/\r$//' "$1"
}

# Renders config with secrets and service discovery if consul-template is in use.
renderAppConfig() {
  if [[ -r "$consul_template_config" ]]; then
    notice "consul-template rendering..."
    templates_root="/etc/myapp/templates"
    consul-template -config "$consul_template_config" \
      -template "${templates_root}/application.ctmpl:/etc/myapp/application.yml" \
      -once
  fi
}

# Waits until Vault sidecar is ready
waitForVault() {
  notice "waiting for local Vault agent..."
  until curl --output /dev/null --silent --head --fail http://localhost:8200/v1/sys/health; do sleep 2; done
}

run() {
  local -a flags
  readarray -t flags < <(loadConfigFile "$flags_file")
  flags+=("-Djava.rmi.server.hostname=$rmi_hostname")

  notice "service starting..."
  exec java "${flags[@]}" -jar "$app_jar" "$@"
}

if [[ "$DEPLOYMENT" == "privatecloud" ]]; then
  rmi_hostname=127.0.0.1 # Work around JMX's dance for port forwarding with Kubernetes internal interface
  waitForVault
fi

renderAppConfig

run "$@"