Merge pull request #1647 from r-birkner/rjb/websockets-blog-post

WebSockets Blog Post

blog/features/websockets-poc.md

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+---
+title: "A step towards WebSockets on the Internet Computer"
+description: Introducing a WebSocket proof-of-concept for the dev community to build on.
+tags: [Devs]
+image: /img/blog/moonshot-2.png
+---
+
+Today, users expect web applications to be fast and snappy: an exchange should update
+the prices in real-time, edits of colleagues should appear immediately when collaborating
+on a document, and comments on social media platforms should update continuously.
+
+To provide such a user-experience, modern web2 applications usually rely on WebSockets,
+which allow establishing a long-lived, full-duplex connection between the frontend
+and backend of an application. This allows for both sides to send data, for example,
+the latest exchange rates, in real-time.
+
+WebSockets can be seen as the next step after [HTTPS outcalls](https://internetcomputer.org/https-outcalls).
+While HTTPS outcalls enable canisters to access publicly-available, off-chain data,
+WebSockets provide long-lived, bi-directional connections with any client.
+
+## Challenges
+
+While WebSockets are a standard in the web2 world, they have not yet
+found their way to web3. We aim to change this for the Internet Computer blockchain.
+
+Unfortunately, this is not a straightforward undertaking due to the decentralized
+nature of the Internet Computer, where the backend does not just run on a single
+centralized entity, but on multiple replica nodes in a subnet. To enable WebSockets
+on the Internet Computer, we need to address the following two main challenges:
+
+_One-to-one connections_ - WebSockets are one-to-one connections: the frontend establishes
+a connection with a single centralized backend. An application on the Internet Computer,
+however, is running distributed across multiple replica nodes in a subnet. In order
+to enable WebSockets, there needs to be a point of consolidation, which provides a
+single contact point for the frontend.
+
+_Long-lived connections_ - WebSockets remain open for long periods of time. The
+canisters on the Internet Computer however follow the actor model, which accepts
+a message, processes it and replies.
+
+To get started and gain experience, we decided to take things one step at a time, and first
+build a proof-of-concept instead of trying to directly integrate WebSockets fully
+into the Internet Computer.
+
+## Architecture
+
+The centerpiece of our proof-of-concept is the WebSocket gateway. It runs on a
+dedicated machine and sits between the frontend, the client’s browser, and the
+backend, the canister on the Internet Computer as the following figure shows.
+
+![WebSockets architecture](../_assets/websockets-architecture.png)
+
+The gateway provides a WebSocket endpoint for the frontend and maintains the connection,
+while it interfaces with the backend on the Internet Computer through query and update calls.
+
+The gateway sends messages coming from the frontend as update calls to the backend
+and it continuously polls the backend for new messages for the frontend. Instead of
+polling, one could have also used HTTPS outcalls to "push" the messages to the gateway.
+However, with an increasing number of messages, polling is more and more efficient.
+
+Despite being a centralized point of failure, the gateway draws on the Internet Computer
+to fulfill its role trustlessly: both the frontend and the backend sign their messages
+such that the gateway cannot tamper with them.
+
+## Try it out!
+
+We have released [the proof-of-concept on Github](https://github.com/dfinity/ic-websocket-poc)
+and invite you to try it out yourself! Use it as an inspiration for your own projects and
+build upon it! Please note that this is a proof-of-concept and requires further
+improvements to enhance security and stability for any use in production. We have
+started [a thread in the developer forum](https://forum.dfinity.org/t/websockets-on-the-ic-a-proof-of-concept/20836)
+and are looking forward to seeing all the applications you built and your feedback.