exp-leader-election

Leader election for nodejs applications

Elect a leader among several nodes using consul.

https://www.consul.io/docs/guides/leader-election.html

Usage

Basic example

Connect to consul and get notified about leadership status.

var leaderElection = require("exp-leader-election");
var service = require("my-little-service");

var config = {
  key: "locks/my-little-service",
  consul : {
    host: "my.consul.hostname"
  }
}

leaderElection(config)
.on("gainedLeadership", function () {
    // Whoo-hoo, we have been elected as leader! Do work.
    service.startDoingWork();
  })
.on("error", function () {
   // Error occured, stop work.
   log.error("Leader election error occured", error);
   service.stopDoingWork();
  });

The let-it-crash way

If you want your application to crash in case of leader election errors, just omit the "error" listener. This is the simplest and most robust way to deal with errors, but it requires that you have a process manager (such as forever or pm2) in place to ensure that the application is restarted again.

Configuration

Full Example

{
  key: "locks/my-little-service", // Only required option
  debug: console.log,
  consul: {
    host: "127.0.0.1",
    port: 8050,
    token: "asdpf2344d083udhd8723",
    ttl: 15,
    lockDelay: 10,
    readWait: 180
  }
}

Consul

• consul.host: Consul hostname or ip (string)
• consul.port: Consul port (number)
• consul.ttl: Tuning, session ttl seconds (number, default 15)
• consul.lockDelay: Tuning, session lock-delay seconds (number, default 10)
• consul.readWait: Tuning, read wait seconds (number, default 180)

To read more about the tuning parameters, see https://www.consul.io/docs/internals/sessions.html

Debugging

• debug: function accepting a variable number of args. Supply if you want to print debugging info.