Consul Sample Project

This project is a simple POC to deal with Consul using NodeJS and HAProxy, inspire by tlhunter example

The goal is only to launch multiple instance of two simple services to see how service discovery are implemented.

I also implemented a leader election following the consul documentation to elect one leader per type of service. As soon as a service is started, he's asking to be the leader and depending of the situation at the time he's asking, he will be or will not be elected.

There is actually 3 folders in this project.

Consul Module folder

It's a module which encapsulate the NodeJS consul package.

HAProxy folder

It is where you put the config for HAProxy.

To start it, only run

haproxy -f advanced.cfg

(You need to have HAProxy installed)

Hello service folder

This is a simple service having a dependency to the service World which expose rest endpoint.

To start a service instance, simply run

cd ./helloservice
node index.js 2727

You can replace 2727 by whatever port you want.

You can run multiple instance on different port to observe service discovery.

There are 3 routes:

• / will retrieve you some data (I dont care of these data), what matter is that helloservice will perform a call to the service he needs, if some are up, one will be chosen else you'll get a 500 error saying no dependencies found.

• /infos will give you the webpid of the process and if it is the master one or not (master = leader)

• /health will let you know if the node is healthy or not

World service folder

Quite the same principle than the previous one, but World service dont have any service dependencies.

To start a service instance, simply run

cd ./worldservice
node index.js 3737

You can replace 3737 by whatever port you want.

You can run multiple instance on different port to observe service discovery.

There are 3 routes:

• / will retrieve you some dumb data

• /infos will give you the webpid of the process and if it is the master one or not (master = leader)

• /health will let you know if the node is healthy or not

Get Started

First launch Consul

consul agent -dev

Then start HAProxy

haproxy -f ./haproxy/advanced.cfg

Finally start as much instance as you want of services (hello and world). Here we will start 1 instance of helloservice 2 of worldservice.

node ./helloservice/index.js 2727

node ./worldservice/index.js 3737
node ./worldservice/index.js 3738

Further Work / Known issue

There is some known issues which need to be fixed, but it was not the purpose here:

• Stoping the master node will not lead to another "master election"

• Once the master node is killed, no nodes can become the master one during the session living time of the original master node (seems a session is not well killed or something like that after a SIGINT)

License

Copyright (c) 2017 reptilbud Licensed under the MIT license