Chaperone

Chaperone is a lean init-style startup manager for Docker-like containers. It runs as a single lightweight full-featured process which runs at the root of a docker container tree and provides all of the following functionality, plus much more:

• Monitoring for all processes in the container, automatically shutting down the container when the last process exits.
• A complete, configurable syslog facility built in and provided on /dev/log so daemons and other services can have output captured. Configurable to handle log-file rotation, duplication to stdout/stderr, and full Linux logging facility, severity support. No syslog daemon is required in your container.
• The ability to start up system services in dependency order, with options for per-service environment variables, restart options, and stdout/stderr capture either to the log service or stdout.
• A built-in cron scheduling service.
• Emulation of systemd notifications (sd_notify) so services can post ready and status notifications to chaperone.
• Process monitoring and zombie elimination, along with organized system shutdown to assure all daemons shut-down gracefully.
• The ability to have an optional controlling process, specified on the docker command line, to simplify creating containers which have development mode vs. production mode.
• Complete configuration using a chaperone.d directory which can be located in various places, and even allows different configurations within the container, triggered based upon which user is selected at start-up.
• Default behavior designed out-of-the-box to work with simple Docker containers for quick start-up for lean containers.
• More...

If you want to try it out quickly, the best place to start is on the chaperone-docker repository page. There is a quick section called "Try it out" that uses images available now on Docker Hub.

For full details of features and usage: see the documentation.

There is some debate about whether docker containers should be transformed into complete systems (so-called "fat containers"). However, it is clear that many containers contain one or more services to provide a single "composite feature", but that such containers need a special, more streamlined approach to managing a number of common daemons.

Chaperone is the best answer I've come up with so far, and was inspired by The Phusion baseimage-docker approach. However, unlike the Phusion image, it does not require adding daemons for logging, system services (such as runit). Chaperone is designed to be self-contained.

Status

Chaperone is now stable and ready for production. If you are currently starting up your container services with Bash scripts, Chaperone is probably a much better choice.

Full status is now part of the documentation.

Downloading and Installing

The easiest way to install chaperoneis usingpip` from the https://pypi.python.org/pypi/chaperone package:

# Ubuntu or debian prerequisites...
apt-get install python3-pip

# chaperone installation (may be all you need)
pip3 install chaperone

License

Copyright (c) 2015, Gary J. Wisniewski garyw@blueseastech.com

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.