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LoadBalancer.java
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LoadBalancer.java
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import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class LoadBalancer {
private static void startLoadBalancer(String schedAlgo) {
try {
// List of WorkerInfo objects. WorkerInfo class has two fields: host, port.
ArrayList<WorkerInfo> workers = new ArrayList<>();
BufferedReader workerFile = new BufferedReader(new FileReader(new File("worker_list.txt")));
// Populate worker list from worker_list.txt.
while (workerFile.read() != -1) {
String[] info = workerFile.readLine().split(",");
workers.add(new WorkerInfo(info[0], Integer.valueOf(info[1])));
}
// WorkerLoads object consists of a list of worker loads, one int load for each worker.
WorkerLoads workerLoads = new WorkerLoads(workers.size());
// Open Load Balancer Socket. This socket acts as a single entry point for all incoming request from Clients.
ServerSocket balancerSocket = new ServerSocket(12345);
int currentWorker = 0;
while (!Thread.interrupted()) {
// Accept a new client connection.
Socket clientSocket = balancerSocket.accept();
if (schedAlgo.equals("RR")) {
// When Round Robin" selected, select Workers in a circular fashion.
currentWorker = (currentWorker + 1) % workers.size();
System.out.println("Selected worker " + currentWorker + ".");
}
else if (schedAlgo.equals("LC")) {
// When Least Connections selected, select Worker with least active connections/requests, and
// increment its load.
currentWorker = workerLoads.getMinLoadServer();
int currLoad = workerLoads.getLoad(currentWorker);
System.out.println("Selected worker " + currentWorker + " with load: " + currLoad + ".");
workerLoads.incrementLoad(currentWorker);
}
// Open connection to selected worker.
Socket workerSocket = new Socket(workers.get(currentWorker).getHost(), workers.get(currentWorker).getPort());
// Start a new thread to serve this request.
Thread lbRequestServer = new Thread(new LBRequestServer(clientSocket, workerSocket, workerLoads, currentWorker));
lbRequestServer.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
// args[0] has the scheduling algorithm parameter(RR and LC, for Round-Robin and Least-Connections respectively).
String schedAlgo = args[0];
startLoadBalancer(schedAlgo);
}
}
class WorkerLoads {
private ArrayList<Integer> workerLoads = new ArrayList<>();
WorkerLoads(int num_servers) {
// Initialize loads of all workers to 0.
for (int i = 0; i < num_servers; i++)
workerLoads.add(0);
}
int getLoad(int index){
return workerLoads.get(index);
}
// Find worker with minimum load.
synchronized int getMinLoadServer() {
int minLoad = workerLoads.get(0), min_ind = 0;
for (int i = 1; i < workerLoads.size(); i++) {
int thisLoad = workerLoads.get(i);
if (thisLoad < minLoad) {
minLoad = thisLoad;
min_ind = i;
}
}
return min_ind;
}
synchronized void incrementLoad(int index){
workerLoads.set(index, workerLoads.get(index) + 1);
}
synchronized void decrementLoad(int index){
workerLoads.set(index, workerLoads.get(index) - 1);
}
}