Comments URL: https://news.ycombinator.com/item?id=48746582

Points: 2

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Comments URL: https://news.ycombinator.com/item?id=48237096

Points: 2

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Asynchronous protocols frequently result in callback-based or generator-style APIs on the client side, which are hard to implement safely and intuitively. For example, consider building a real-time SDK for something like NATS. Once a message arrives, you need to invoke a user-defined callback to handle it. At that point, you're faced with a design decision: either call the callback synchronously (which risks blocking the socket reading loop), or do it asynchronously (which raises issues like backpressure handling).

Also, SDKs are often developed by different people, each with their own design philosophy and coding style, leading to inconsistency and subtle bugs.

So this isn't only about NATS. Just last week, we ran into two critical bugs in two separate Kafka SDKs at work.

I'd like to share that we've just released Centrifugo v6 - a major update of scalable WebSocket server. The release addresses some usability pain points and adds nice features and more observability.

Centrifugo is an open-source standalone server written in Go – https://github.com/centrifugal/centrifugo. Centrifugo can instantly deliver messages to application online users connected over supported transports (WebSocket, HTTP-streaming, Server-Sent Events (EventSource), GRPC, WebTransport). Centrifugo has the concept of a channel – so it's a user-facing PUB/SUB server. Everything implemented in a language-agnostic way – so Centrifugo can be used in combination with any frontend or backend stack.

These days we also provide Centrifugo PRO version – and trying to find a balance to be sustainable.

The server is based on the open-source Centrifuge library - https://github.com/centrifugal/centrifuge, so many improvements mentioned in Centrifugo v6 release blog post (even those for Centrifugo PRO) may be used just as a library in Go application.

We provide real-time SDKs for popular client environments – for browser and mobile development – they connect to both Centrifuge library based servers and Centrifugo server.

Generally Centrifugal ecosystem provides a good alternative to Socket.IO and cloud services like Pusher.com and Ably.com

Will be happy to answer on any questions

Comments URL: https://news.ycombinator.com/item?id=42723631

Points: 2

# Comments: 1

Let me share a bit more about Centrifugo transport choices. It’s not just about supporting multiple transports — developers can also choose between bidirectional and unidirectional communication models, depending on their needs.

For scenarios where stable subscriptions are required without sending data from the client to the server, Centrifugo seamlessly supports unidirectional transports like SSE, HTTP-streaming, unidirectional gRPC streams, and even unidirectional WebSockets (this may sound kinda funny for many I guess). This means integration is possible without relying on client-side SDKs.

However, Centrifugo truly shines in its bidirectional communication capabilities. Its primary transport is WebSocket – with JSON or Protobuf protocols, with SSE/HTTP-streaming fallbacks that are also bidirectional — an approach reminiscent of SockJS, but with more efficient implementation and no mandatory sticky sessions. Sticky sessions is an optimization in Centrifugo, not a requirement. It's worth noting that SSE only supports JSON format, since binary is not possible with it. This is where HTTP-streaming in conjuction with ReadableStream browser API can make much more sense!

I believe Centrifugo gives developers the flexibility to choose the transport and communication style that best fits their application's needs. And it scales good out of the box to many nodes – with the help of Redis or Nats brokers. Of course this all comes with limitations every abstraction brings.

Comments URL: https://news.ycombinator.com/item?id=42093194

Points: 4

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Comments URL: https://news.ycombinator.com/item?id=41307612

Points: 1

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Comments URL: https://news.ycombinator.com/item?id=40256780

Points: 1

# Comments: 0

What I'd like to add is that Centrifugo also supports HTTP-streaming – not mentioned by the OP – but this is a transport which has advantages over Eventsource - like possibility to send POST body on initial request from web browser (with SSE you can not), it supports binary, and with Readable Streams browser API it's widely supported by modern browsers.

Another thing I'd like to mention about Centrifugo - it supports bidirectional WebSocket fallbacks with EventSource and HTTP-streaming, and does this without sticky sessions requirement in distributed scenario. I guess nobody else have this at this point. See https://centrifugal.dev/blog/2022/07/19/centrifugo-v4-releas.... Which solves one more practical concern. Sticky sessions is an optimization in Centrifugo case, not a requirement.

If you are interested in topic, we also have a post about WebSocket scalability - https://centrifugal.dev/blog/2020/11/12/scaling-websocket - it covers some design decisions made in Centrifugo.

Comments URL: https://news.ycombinator.com/item?id=38789840

Points: 3

# Comments: 0

Let's say we have a system with 3 participants like this:

Client (browser, mobile device, etc.) —> WebSocket server (the subject to implement here) —> Backend server (any custom server in any language with good GRPC support).

Then the mechanics is as follows:

* Client establishes WebSocket connection with WebSocket server

* Client can optionally subscribe to channels. Subscriptions to channels are multiplexed over a single WebSocket connection.

* Upon receiving WebSocket connection (or subscription to channel) server can open unidirectional or bidirectional stream with the configured backend which implements GRPC service.

* Backend may stream data to connections or to channel subscriptions over established GRPC streams. Data from GRPC streams will be transformed to WebSocket messages and delivered to clients with minimal latency.

* Additionally, client can stream data to the backend server (if bidirectional GRPC streams are used). I.e. client sends WebSocket messages, those will be transformed to GRPC messages by WebSocket server and delivered to the application backend.

As a result we have a system which allows to quickly create individual streams by using strict GRPC contract but terminating connections over WebSocket transport. So it works well in web browsers. After that no need to write WebSocket protocol, client implementation, handle WebSocket connection. This all will be solved by a suggested WebSocket server and its client SDKs.

The mechanics is similar to Websocketd (https://github.com/joewalnes/websocketd), but instead of creating OS processes we create GRPC streams. The difference from grpc-web (https://github.com/grpc/grpc-web) is that we provide streaming capabilities but not exposing GRPC contract to the client - just allowing to stream any data as payload (both binary and text) with some wrappers from our client SDKs side for managing subscriptions. I.e. it's not native GRPC streams on the client side - we expose just Connection/Subscription object to stream in both directions. GRPC streams used only for communication between WebSocket server and backend. To mention - grpc-web does not support all kinds of streaming now (https://github.com/grpc/grpc-web#streaming-support) while proposed solution can. This all should provide a cross-platform way to quickly write streaming apps due to client SDKs and language-agnostic nature of GRPC.

I personally see both pros and cons in this scheme (without concentrating on both too much here to keep the question short). I spent some time thinking about this myself, already have some working prototypes – but turned out need more opinions before moving forward with the idea and releasing this, kinda lost in doubts.

My main question - whether this seems interesting for someone here? Do you find this useful and see practical value?

Comments URL: https://news.ycombinator.com/item?id=37130538

Points: 1

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Comments URL: https://news.ycombinator.com/item?id=32839682

Points: 1

# Comments: 0

I am the author of Centrifugo server (https://github.com/centrifugal/centrifugo) - where the main protocol is WebSocket. Agree with many points in post – and if there is a chance to build sth without replacing stateless HTTP to persistent WebSocket (or EventSource, HTTP-streaming, raw TCP etc) – then definitely better to go without persistent connections.

But there are many tasks where WebSockets simply shine – by providing a better UX, providing a more interactive content, instant information/feedback. This is important to keep - even if underlying stack is complicated enough. Not every system need to scale to many machines (ex. multiplayer games with limited number of players), corporate apps not really struggle from massive reconnect scenarios (since number of concurrent users is pretty small), and so on. So WebSockets are definitely fine for certain scenarios IMO.

I described some problems with WebSockets Centrifugo solves in this blog post - https://centrifugal.dev/blog/2020/11/12/scaling-websocket. I don't want to say there are no problems, I want to say that WebSockets are fine in general and we can do some things to deal with things mentioned in the OP's post.

Comments URL: https://news.ycombinator.com/item?id=28379323

Points: 2

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