Startup.cs

## Startup.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.DataProtection;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using StackExchange.Redis;

namespace SessionExample
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            //retrieve connectoin info from environment variables in this sample
            var host = Environment.GetEnvironmentVariable("REDIS_SESSION_SERVICE_HOST");
            var port = Environment.GetEnvironmentVariable("REDIS_SESSION_SERVICE_PORT");
            var conn = $"{host}:{port}";
            var redis = ConnectionMultiplexer.Connect(conn);

            services.AddDataProtection()
                .PersistKeysToRedis(redis, "DataProtection-Keys");
            services.AddDistributedRedisCache(option =>
            {
                option.Configuration = conn;
                option.InstanceName = "master";
            });
            services.AddSession();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            app.UseSession();

            loggerFactory.AddConsole();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            //This sample is described in https://docs.microsoft.com/en-us/aspnet/core/fundamentals/app-state
            app.Map("/session", subApp =>
            {
                subApp.Run(async context =>
                {
                    // uncomment the following line and delete session coookie to generate an error due to session access after response has begun
                    // await context.Response.WriteAsync("some content");
                    RequestEntryCollection collection = GetOrCreateEntries(context);
                    collection.RecordRequest(context.Request.PathBase + context.Request.Path);
                    SaveEntries(context, collection);
                    if (context.Session.GetString("StartTime") == null)
                    {
                        context.Session.SetString("StartTime", DateTime.Now.ToString());
                    }

                    await context.Response.WriteAsync("<html><body>");
                    await context.Response.WriteAsync($"Counting: You have made {collection.TotalCount()} requests to this application.<br><a href=\"/\">Return</a>");
                    await context.Response.WriteAsync("</body></html>");
                });
            });

            //please add code to confirm session is wokring.
            //you can find full code https://github.com/tanaka-takayoshi/aspnetcore-redis-session-example
        }
    }
}