Analysis of the solution to Nginx Session sharing problem

package com.zn.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/nginxSessionServlet")
public class SessionIPServlet extends HttpServlet {
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("Current request port: "+request.getLocalPort());
    String action = request.getParameter("action");
    //Store a data in Session if(action.equals("setSession")){
      request.getSession().setAttribute("username","zhangsan");
    }else if(action.equals("getSession")){
      response.getWriter().write((String)request.getSession().getAttribute("username"));
    }
  }

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request,response);
  }
}

upstream myserver{
     ip_hash;
     server 127.0.0.1:8080;
     server 127.0.0.1:8081;
  }
  server{
    listen 81;
    server_name www.bproject.com;
    location / {
      root html;
      proxy_pass http://myserver;
      index index.html index.htm;
    }
  }

<!--Spring boot and redis application basic environment configuration-->
    <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-redis -->
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-redis</artifactId>
    </dependency>

    <!--Spring session and redis application basic environment configuration, you need to enable redis before you can use it, otherwise you will get an error when starting Spring boot-->
    <dependency>
      <groupId>org.springframework.session</groupId>
      <artifactId>spring-session-data-redis</artifactId>
    </dependency>

@RestController
public class SessionController {

  @RequestMapping("/setSession")
  public String setSession(HttpServletResponse response, HttpServletRequest request) throws IOException {
    request.getSession().setAttribute("username","wang");
    return "success";
  }

  @RequestMapping("/getSession")
  public String getSession(HttpServletRequest request,HttpServletResponse response){
    String username = (String) request.getSession().getAttribute("username");
    return username;
  }
}

server.port=8082
#server.port=8083

#redis configuration spring.redis.password: wang2003