NATS Logo by Example

Core Publish-Subscribe in Messaging

This example demonstrates the core NATS publish-subscribe behavior. This is the fundamental pattern that all other NATS patterns and higher-level APIs build upon. There are a few takeaways from this example:

  • Delivery is an at-most-once. For MQTT users, this is referred to as Quality of Service (QoS) 0.
  • There are two circumstances when a published message won’t be delivered to a subscriber:
    • The subscriber does not have an active connection to the server (i.e. the client is temporarily offline for some reason)
    • There is a network interruption where the message is ultimately dropped
  • Messages are published to subjects which can be one or more concrete tokens, e.g. greet.bob. Subscribers can utilize wildcards to show interest on a set of matching subjects.
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$ nbe run messaging/pub-sub/dotnet2
View the source code or learn how to run this example yourself


Install NuGet packages NATS.Net, NATS.Client.Serializers.Json and Microsoft.Extensions.Logging.Console.

using Microsoft.Extensions.Logging;
using NATS.Client.Core;
using NATS.Client.Serializers.Json;

using var loggerFactory = LoggerFactory.Create(builder => builder.AddConsole());
var logger = loggerFactory.CreateLogger("NATS-by-Example");

NATS_URL environment variable can be used to pass the locations of the NATS servers.

var url = Environment.GetEnvironmentVariable("NATS_URL") ?? "";

Connect to NATS server. Since connection is disposable at the end of our scope we should flush our buffers and close connection cleanly.

var opts = new NatsOpts
    Url = url,
    LoggerFactory = loggerFactory,
    SerializerRegistry = NatsJsonSerializerRegistry.Default,
    Name = "NATS-by-Example",
await using var nats = new NatsConnection(opts);

Subscribe to a subject and start waiting for messages in the background.

await using var sub = await nats.SubscribeCoreAsync<Order>("orders.>");

logger.LogInformation("Waiting for messages...");
var task = Task.Run(async () =>
    await foreach (var msg in sub.Msgs.ReadAllAsync())
        var order = msg.Data;
        logger.LogInformation("Subscriber received {Subject}: {Order}", msg.Subject, order);


Let’s publish a few orders.

for (int i = 0; i < 5; i++)
    logger.LogInformation("Publishing order {Index}...", i);
    await nats.PublishAsync($"{i}", new Order(OrderId: i));
    await Task.Delay(500);

We can unsubscribe now all orders are published. Unsubscribing or disposing the subscription should complete the message loop and exit the background task cleanly.

await sub.UnsubscribeAsync();
await task;

That’s it! We saw how we can subscribe to a subject and publish messages that would be seen by the subscribers based on matching subjects.


public record Order(int OrderId);


info: NATS.Client.Core.NatsConnection[1001]
      Try to connect NATS nats://nats:4222
info: NATS.Client.Core.Internal.NatsReadProtocolProcessor[1005]
      Received server info: ServerInfo { Id = NA5KDEZVXJXTIYMQAXRROBZL3WMLCO63YO2Z5QJOABXIFQZDN3AKTBF2, Name = NA5KDEZVXJXTIYMQAXRROBZL3WMLCO63YO2Z5QJOABXIFQZDN3AKTBF2, Version = 2.10.4, ProtocolVersion = 1, GitCommit = abc47f7, GoVersion = go1.21.3, Host =, Port = 4222, HeadersSupported = True, AuthRequired = False, TlsRequired = False, TlsVerify = False, TlsAvailable = False, MaxPayload = 1048576, JetStreamAvailable = True, ClientId = 5, ClientIp =, Nonce = , Cluster = , ClusterDynamic = False, ClientConnectUrls = , WebSocketConnectUrls = , LameDuckMode = False }
info: NATS.Client.Core.NatsConnection[1001]
      Connect succeed NATS-by-Example, NATS nats://nats:4222
info: NATS-by-Example[0]
      Waiting for messages...
info: NATS-by-Example[0]
      Publishing order 0...
info: NATS-by-Example[0]
      Subscriber received Order { OrderId = 0 }
info: NATS-by-Example[0]
      Publishing order 1...
info: NATS-by-Example[0]
      Subscriber received Order { OrderId = 1 }
info: NATS-by-Example[0]
      Publishing order 2...
info: NATS-by-Example[0]
      Subscriber received Order { OrderId = 2 }
info: NATS-by-Example[0]
      Publishing order 3...
info: NATS-by-Example[0]
      Subscriber received Order { OrderId = 3 }
info: NATS-by-Example[0]
      Publishing order 4...
info: NATS-by-Example[0]
      Subscriber received Order { OrderId = 4 }
info: NATS-by-Example[0]
info: NATS-by-Example[0]
info: NATS.Client.Core.NatsConnection[1001]
      Disposing connection NATS-by-Example


Note, playback is half speed to make it a bit easier to follow.