Container Restart Helper

injectRestartHelper

The injectRestartHelper option expects a boolean which decides if DevSpace should inject a restart helper and override the ENTRYPOINT+CMD of the image in runtime during the build process which wraps the regular container start command and allows to restart the regular container start command without terminating/recreating the container.

How does it work?

The idea of the restart helper is to start the restart helper script as PID 1 inside the conainer. This script will then start the original container entrypoint which will run your application. If a restart is triggered, the restart helper will just restart the application again.

Automatic Restart On File Change

The restart helper per se does not do much except restarting your application if it has been killed. You can combine this config option with the post-sync command restartContainer: true which will effectively restart your application inside the container every time DevSpace syncs files into the container.

Default Value For injectRestartHelper

injectRestartHelper: false

Example: Inject Restart Helper

images:
  backend:
    image: john/appbackend
  frontend:
    image: john/appfrontend
    injectRestartHelper: true

Trigger a Restart

You can restart a pod that has a restart helper injected with devspace itself:

devspace restart -n my-namespace
devspace restart -n my-namespace --pod my-pod
devspace restart -n my-namespace --label-selector abc=def

Restart a pod via kubectl:

kubectl exec my-pod -- sh -c 'PID=$(cat /.devspace/devspace-pid) && rm /.devspace/devspace-pid && kill -9 -$PID' 

You can also manually trigger a restart through the restart helper by doing the following (same as with kubectl):

# 1. Get the PID of your applications process
PID=$(cat /.devspace/devspace-pid)

# 2. Remove the PID file to tell the restart helper that this is an intended restart
# (otherwise the restart helper will terminate as well which will kill the container)
rm /.devspace/devspace-pid

# 3. Kill the application process group (restart helper on PID 1 will detect this and restart it again)
kill -9 -$PID

Automatic Restart On File Change

This is exactly what DevSpace is doing when the post-sync command restartContainer: true is configured.

Restart Helper Script

#!/bin/sh
#
# A process wrapper script to simulate a container restart. This file was injected with devspace during the build process
#
set -e
pid=""
trap quit TERM INT
quit() {
  if [ -n "$pid" ]; then
    kill $pid
  fi
}
while true; do
  setsid "$@" &
  pid=$!
  echo "$pid" > /.devspace/devspace-pid
  set +e
  wait $pid
  exit_code=$?
  if [ -f /.devspace/devspace-pid ]; then
    rm -f /.devspace/devspace-pid
    printf "\nContainer exited with $exit_code. Will restart in 7 seconds...\n"
    sleep 7
  fi
  set -e
  printf "\n\n############### Restart container ###############\n\n"
done

Providing a custom restart helper script or changing the existing script

DevSpace provides a way to change the existing restart helper script by defining the option restartHelperPath:

images:
  frontend:
    image: john/appfrontend
    injectRestartHelper: true
    restartHelperPath: path/to/restarthelper.sh

DevSpace will now inject this script instead of the bundled restart helper script (see above). You can also specify an URL instead of a local path. This can be handy if you want to start up the application in a special way or want to make adjustments to the existing restart helper script.