How to make Redis notify my service about events

Question

I have a remote computer with Redis. From time to time new entries are added to it (key-value pair). I want Redis to send notifications to my C# Service about events like this (i'm interested in value part). I've searched online and found simple code example to subscribe my Service to Redis. How to make Redis send notifications?

Service:

public partial class ResultsService : ServiceBase
{
    private ConnectionMultiplexer connection = ConnectionMultiplexer.Connect(ConfigurationManager.AppSettings["RedisConnection"]);

    private const string ChatChannel = "__keyspace@0__:*";

    public VerificationResultsService()
    {
        InitializeComponent();
    }

    protected override void OnStart(string[] args)
    {
        Start();
    }

    public void Start()
    {
        var pubsub = connection.GetSubscriber();

        pubsub.Subscribe(ChatChannel, (channel, message) => MessageAction(message));

        while (true)
        {

        }
    }

    private static void MessageAction(RedisValue message)
    {
         // some handler...
    }
}

Answer 1

Making redis send automatic keyspace notifications is a redis server configuration piece, which can be enabled via the .conf file (notify-keyspace-events), or via CONFIG SET at runtime; the documentation for this is here.

You can see how this works with example code:

using StackExchange.Redis;
using System;
using System.Linq;

static class P
{
    private const string ChatChannel = "__keyspace@0__:*";
    static void Main()
    {
        // connect (allowAdmin just lets me use ConfigSet)
        using var muxer = ConnectionMultiplexer.Connect("127.0.0.1,allowAdmin=true");

        // turn on all notifications; note that this is server-wide
        // and is NOT just specific to our connection/code
        muxer.GetServer(muxer.GetEndPoints().Single())
             .ConfigSet("notify-keyspace-events", "KEA"); // KEA=everything

        // subscribe to the event
        muxer.GetSubscriber().Subscribe(ChatChannel,
            (channel, message) => Console.WriteLine($"received {message} on {channel}"));

        // stop the client from exiting
        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }
}

which works like:

---

However, in many scenarios you may find that this is too "noisy", and you may prefer to use either a custom named event that you publish manually when you do things that need notification, or (again manually) you could make use of the streams features to consume a flow of data (streams can be treated as a flow of events in the "things that happened" sense, but they are not delivered via pub/sub).