Enable Leader Election

This guide will show you how to enable leader election for your application.

Enable leader election in manifest

.nais/app.yaml

spec:
  leaderElection: true

Using leader election in your application (simple API)

JavacURLPythonTypeScript

// Implementation of getJSONFromUrl is left as an exercise for the reader
class Leader {
    public static boolean isLeader() {
        String electorUrl = System.getenv("ELECTOR_GET_URL");
        JSONObject leaderJson = getJSONFromUrl(electorUrl);
        String leader = leaderJson.getString("name");
        String hostname = InetAddress.getLocalHost().getHostname();

        return hostname.equals(leader);
    }
}

$ kubectl exec -it elector-sidecar-755b7c5795-7k2qn -c debug bash
root@elector-sidecar-755b7c5795-7k2qn:/# curl ${ELECTOR_GET_URL}
{"name":"elector-sidecar-755b7c5795-2kcm7","last_update":"2022-10-18T10:59:58Z"}

import os
import socket
import requests

def is_leader():
    elector_url = os.getenv("ELECTOR_GET_URL")
    resp = requests.get(elector_url)
    leader = resp.json()["name"]
    return socket.gethostname() == leader    

import * as os from 'node:os'

export async function isLeader(): Promise<boolean> {
    const hostname = os.hostname()
    const electorUrl = process.env.ELECTOR_GET_URL

    const electorResponse = await fetch(electorUrl)
    if (!electorResponse.ok) {
        throw new Error(
            `Failed to fetch leader from ${electorUrl}, response: ${electorResponse.status} ${electorResponse.statusText}`,
        )
    }
    const result: { name: string; last_update: string } = await electorResponse.json()

    return result.name === hostname
}

Using leader election in your application (Server Sent Events API)

Help Wanted! Please contribute with examples on how to use the Server Sent Events API.