NATS Logo by Example

Intro in Services Framework

NATS services have always been straightforward to write. However, with the services framework, the NATS client library further simplifies the building, discovery and monitoring of services. The framework automatically places all subscriptions in a queue group and provides functionality for building subject hierarchies and their handlers.

Without any additional effort, the library enables automatic service discovery and status reporting. The NATS CLI nats micro command provides a simple way to query and report all the services using this framework.

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

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

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);
var svc = new NatsSvcContext(nats);

Defining a Service

This will create a service definition. Service definitions are made up of the service name (which can’t have things like whitespace in it), a version, and a description. Even with no running endpoints, this service is discoverable via the micro protocol and by service discovery tools like nats micro. All of the default background handlers for discovery, PING, and stats are started at this point.

var service = await svc.AddServiceAsync(new NatsSvcConfig("minmax", "0.0.1")
    Description = "Returns the min/max number in a request"

Each time we create a service, it will be given a new unique identifier. If multiple copies of the minmax service are running across a NATS subject space, then tools like nats micro will consider them like unique instances of the one service and the endpoint subscriptions are queue subscribed, so requests will only be sent to one endpoint instance at a time. TODO: service.Info

Adding endpoints

Groups serve as namespaces and are used as a subject prefix when endpoints don’t supply fixed subjects. In this case, all endpoints will be listening on a subject that starts with minmax.

var root = await service.AddGroupAsync("minmax");

Adds two endpoints to the service, one for the min operation and one for the max operation. Each endpoint represents a subscription. The supplied handlers will respond to minmax.min and minmax.max, respectively.

await root.AddEndpointAsync(HandleMin, "min", serializer: NatsJsonSerializer<int[]>.Default);
await root.AddEndpointAsync(HandleMax, "max", serializer: NatsJsonSerializer<int[]>.Default);

Make a request of the min endpoint of the minmax service, within the minmax group. Note that there’s nothing special about this request, it’s just a regular NATS request.

var min = await nats.RequestAsync<int[], int>("minmax.min", new[]
    -1, 2, 100, -2000
}, requestSerializer: NatsJsonSerializer<int[]>.Default);
logger.LogInformation("Requested min value, got {Min}", min.Data);

Make a request of the max endpoint of the minmax service, within the minmax group.

var max = await nats.RequestAsync<int[], int>("minmax.max", new[]
    -1, 2, 100, -2000
}, requestSerializer: NatsJsonSerializer<int[]>.Default);
logger.LogInformation("Requested max value, got {Max}", max.Data);

The statistics being managed by micro should now reflect the call made to each endpoint, and we didn’t have to write any code to manage that. TODO: service.Stats

That’s it!


ValueTask HandleMin(NatsSvcMsg<int[]> msg)
    var min = msg.Data.Min();
    return msg.ReplyAsync(min);

ValueTask HandleMax(NatsSvcMsg<int[]> msg)
    var min = msg.Data.Max();
    return msg.ReplyAsync(min);


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 = NBNKAKMI2JMCWMZGM53FPYI2VYTYKXRKICP6BA37JEKXHKVQPJPKDLYV, Name = NBNKAKMI2JMCWMZGM53FPYI2VYTYKXRKICP6BA37JEKXHKVQPJPKDLYV, 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]
      Requested min value, got -2000
info: NATS-by-Example[0]
      Requested max value, got 100
info: NATS-by-Example[0]
info: NATS.Client.Core.NatsConnection[1001]
      Disposing connection NATS-by-Example


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