hanoverd

README

This project is in the early prototype / dreaming phase

Hanoverd - The docker handover daemon

Hanoverd ("Hanover-Dee") is responsible for managing seamless transitions from one application version to another with Docker containers.

Installation

Hanoverd currently requires the ability to mess with iptables. This can be achieved with setcap to avoid using root.

A suitably capable iptables command must be on the $PATH. This can be achieved with this command:

cp $(which iptables) .
sudo setcap 'cap_net_admin,cap_net_raw=+ep' iptables
PATH=.:$PATH hanoverd

(or you can use some directory other than .).

User experience

• You run one hanoverd per application you wish to run in Docker.
• You run hanoverd in a directory containing a Dockerfile.
• Starting hanoverd causes that Dockerfile to be built and the application is started.
• Sending hanoverd a signal results in hanoverd rebuilding the container and transitioning to the new version.
• When the new version successfully accepts a connection, the new version becomes live.
• If the new version fails to accept any connection, the old version will chug along happily until a new request comes in to start a new application version.

Building and running

First build it:

$ go get -v
$ go build -v

Then launch it (in a directory with a Dockerfile!):

$ ./hanoverd

Environment variables which the docker client (and boot2docker) use can be set first.

DOCKER_CERT_PATH DOCKER_HOST DOCKER_TLS_VERIFY

Method

• Hanoverd is responsible for listening on externally visible sockets and forwards them to the currently active docker application.
• Hanoverd can be signalled via POSIX signals or via a HTTP ping.

Plans

• Hanoverd is not currently responsible for receiving a hook to run updates - that may be the responsibility of another application
• Hanoverd can provide log messages live via a web interface.
• "Power on self test" allows hanoverd to also run some tests before declaring the new container ready to go live.