Difference between Connect Publish and Jetstream Publish

[alberk8]

I have Jetstream created and it seems that I can publish using the connection publish as well as the natsjscontext publish. May I know the difference and the pro and cons? Thank you.

 var opt = new NatsOpts
 {
     Url = "nats://localhost:4222",
     SerializerRegistry = NatsJsonSerializerRegistry.Default,
     Name = "Nats_Connect",
 };

 var connect = new NatsConnection(opt);

 var jsContext = new NatsJSContext(connect);
 var streamConfig = new StreamConfig("TestStream", new[] { "TestSubject" }); 
 await jsContext.UpdateStreamAsync(streamConfig);
 
 await connect.PublishAsync("TestSubject", new TestPerson { Name = "Connect Publish" });
 await jsContext.PublishAsync<TestPerson>("TestSubject", new TestPerson { Name = "JetStream Publish" });

[mtmk]

JetStream publish returns an acknowledgment that message is persisted (at-least-once). Core (connection) publish is fire-and-forget or delivered at-most-once semantics.

You should check for ack in case of errors and take action based on your application requirements:

// nothing to check. fire and forget
await connect.PublishAsync("TestSubject", new TestPerson { Name = "Connect Publish" });

// check ack
var ack = await jsContext.PublishAsync<TestPerson>("TestSubject", new TestPerson { Name = "JetStream Publish" });

ack.EnsureSuccess(); // throws exception

// or

if (ack.IsSuccess())
{
  // ...
}

[alberk8]

I did check that Core publish to the Jetstream subject and it did go through and is persisted on Jetstream. The only thing is there is no acknowledgement.

[mtmk]

yes, with core also there is no guarantee that the message will be persisted

[mtmk]

also note you can get better performance with batch publishing in JetStream

// dotnet add package NATS.Net
using NATS.Net;
using NATS.Client.JetStream;
using NATS.Client.JetStream.Models;

await using var nc = new NatsClient();

INatsJSContext js = nc.CreateJetStreamContext();

// Create a stream
var streamConfig = new StreamConfig(name: "example-stream", subjects: ["example-subject"]);
await js.CreateStreamAsync(streamConfig);

// Publish a message
{
    PubAckResponse ack = await js.PublishAsync("foo", "Hello, JetStream!");
    ack.EnsureSuccess();
}

// Publish messages concurrently
List<NatsJSPublishConcurrentFuture> futures = new();
for (var i = 0; i < 500; i++)
{
    NatsJSPublishConcurrentFuture future
        = await js.PublishConcurrentAsync("foo", "Hello, JetStream 1!");
    futures.Add(future);
}

foreach (var future in futures)
{
    await using (future)
    {
        PubAckResponse ack = await future.GetResponseAsync();
        ack.EnsureSuccess();
    }
}