Use a simple round robin to select instances

Signed-off-by: kvmw <[email protected]>

Author: kvmw

packages/greeter/server.js

@@ -2,18 +2,37 @@ import axios from 'axios';
 import express from 'express';
 import { env, eureka } from '@greeting/shared';
 
+class SimpleRoundRobin {
+  constructor(eurekaClient) {
+    this.eurekaClient = eurekaClient;
+    this.index = 0;
+  }
+
+  next() {
+    const instances =
+      this.eurekaClient
+        .getInstancesByAppId('GREETER-MESSAGES')
+        ?.filter((instance) => instance.status === 'UP') || [];
+
+    if (instances.length === 0) {
+      return new Error('No instances of GREETER-MESSAGES available');
+    }
+    this.index = this.index % instances.length;
+    const instance = instances[this.index];
+    this.index++;
+    return instance.hostName;
+  }
+}
+
 const app = express();
 const eurekaClient = await eureka.getClient(env.port);
-
-const lookupService = () => {
-  return eurekaClient.getInstancesByAppId('GREETER-MESSAGES')[0]?.hostName;
-};
+const selector = new SimpleRoundRobin(eurekaClient);
 
 app.get('/hello', async (req, res) => {
   const salutation = req.query.salutation || 'Hello';
   const name = req.query.name || 'Bob';
 
-  const url = `https://${lookupService()}/greeting?salutation=${salutation}&name=${name}`;
+  const url = `https://${selector.next()}/greeting?salutation=${salutation}&name=${name}`;
 
   const response = await axios.get(`${url}`, {
     headers: {

packages/shared/src/eureka.js

@@ -25,6 +25,10 @@ const getClient = async (port) => {
         $: port,
         '@enabled': true,
       },
+      securePort: {
+        $: port,
+        '@enabled': true,
+      },
       vipAddress: 'UNKNOWN',
       dataCenterInfo: {
         '@class': 'com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo',