Docker Service Discovery

This projects provides a distributed, reliable key-value store setup used for service-discovery within a docker swarm environment.

Introduction

In a docker swarm environment there is no way to control the startup order of nodes withing the swarm. As some services need to be deployed redundant in a master/slave setup a mechanism is needed to control the lifecycle of services within the swarm.

My docker-cluster-controller project provides a python class to manage this service lifecycle from within a docker-entrypoint script.

However a central key-value store is required to store an instances properties like its role in a cluster. This project provides the Dockerfile to create a etcd image and a compose file which can be used to start a etcd cluster.

ETCD Image

The image can be build using docker build -t etcd . and needs some environment variable's set to operate:

Variable	Description
ETCD_UUID	A UUID for the cluster (in a bash shell use uuidgen to generate a UUID)
ETCD_CLUSTER_SIZE	The number of nodes in the cluster, a cluster should have a minimum of 2 nodes.
ETCD_DISCOVERY_NODE	The discovery node

To start a cluster a so called bootstrap node is needed. This node is only required during the startup of the cluster.

ETCD Swarm Setup

The swarm has two networks: sd_backend and sd_frontend. The backend network is used for communication between the ETCD nodes and the bootstrap node. The frontend network can be used to have other containers connect to the ETCD cluster.

Usage

docker build -t etcd .
docker stack deploy -c docker-swarm.yml etcd-cluster

Check the cluster:

docker stack ps etcd-cluster

Check the logs:

docker service logs etcd-cluster_bootstrap-service-discovery
docker service logs etcd-cluster_service-discovery