Unblocker

Docker Global Hackday #2 project

What does unblocker do?

The idea is that if you push a new image to a Docker registry, all the running containers with an old version of that image are automatically replaced by the new version.

How does unblocker work?

Using a Consul watch we watch the newimage event with unblocker.py as it's handler. This means that when the newimage event is triggered unblocker.py gets called with the event's payload as input.

Unblocker then does the following things:

• Pull the new image
• Find containers running an older version of the same image by image repo/name
• Start the same amount of containers with the new image
• Stop the old containers

The end result is that a Docker Registry only has to fire the newimage event to automatically update all running containers to the new image :)

Demo

To try it yourself use below instructions as a guideline:

# Build the consul-python container
docker build -t consul-python dockerfiles/consul-python/
# Start the container
fig up
# Enter the container
docker exec -ti `docker ps -lq` /bin/bash
# Start an ubuntu 14.04 & 14.10 container
docker run -d ubuntu:14.04 sleep 3000 && docker run -d ubuntu:14.10 sleep 3000
# List the currently running containers
docker ps
# Pretend we are are a Docker Registry which has just received an updated image
consul event -http-addr localhost:8500 -name newimage '{"image":"ubuntu", "tag":"14.04"}'
# List the new running containers
docker ps
# Pretend we are are a Docker Registry which has just received an updated image for the second time
consul event -http-addr localhost:8500 -name newimage '{"image":"ubuntu", "tag":"14.10"}'
# List the new running containers
docker ps