This repository is a proof-of-concept for Blue/Green deployments with HAProxy, Docker and docker-compose. It's mostly an experiment, for Blue/Green deployments at scale, there's already an interesting amount of solutions. For instance, kubernetes, docker-swarm and the good old fleet.

However, theses solutions take some time (weeks at least) to set up if you have an already existing infrastructure. In the meantime, blue/green deployments with Docker can be a good replacement for blue/green deployments consisting in spawning/killing instances in the cloud: they run much much faster (approximately 300x faster :) ) and don't imply tweaking autoscaling-groups, load-balancersor DNS configuration.

The best way to get started is to spawn the sample_service included in the repo. For that, one would just run:

docker-compose up --build

It will start an HAProxy container (bound to the hosts network) listening on port 8000 and two instances of our sample_service a blue and a green one.

You can alter the code of sample_service.go (change hello to ola for instance) and then run ./deploy_blue_green.sh. You'll see your new image being built and you application be updated in a blue/green way :)

A bit more interesting maybe, put a very long time.Sleep at the beginning of the main() function of sample_service.go, so that your service never really starts and deploy the new version of your code.

You'll see that HAProxy won't call your blue instance this it doesn't pass HAProxy's health check... even better, you'll have the deployment script fail. If it runs on Jenkins, TravisCI or whatever, you won't miss the red build.

To be written (deploying images hosted on DockerHub, in-depth explanation about how this setup works, how to monitor HAProxy and - more important - a beautiful schema.

• Sort of unit test the script's behaviour
• Implement a rollback feature (ultimately this one would remove images that don't start from DockerHub or at least make sure the latest tag isn't pointing to one of them).

• Étienne Lafarge <etienne_dot_lafarge__at__gmail_dot_com>