Ably — Realtime Infrastructure as a Service

Ably — Realtime Infrastructure as a Service

Overview

Ably is a managed pub/sub platform. An application publishes messages to named channels and every subscribed client receives them over a WebSocket connection that the SDK keeps alive and resumes after a short network drop. On top of plain messaging it provides presence (who is on a channel), message history, token authentication with per-channel permissions, and a separate Chat SDK with rooms, typing indicators and reactions.

Two clients exist in the ably package: Ably.Realtime holds a connection and can subscribe; Ably.Rest is stateless HTTP and is the right choice for servers and serverless functions that only publish or issue tokens.

Instructions

Install

npm install ably
npm install @ably/chat        # Chat SDK, optional; built on top of ably
npm install jsonwebtoken      # server side, to sign tokens for browser clients

Create an app in the Ably dashboard and copy an API key. A key looks like I2E_JQ.OqUdfg:EVKVT...: the part before the colon is the key name, the part after it is the secret. Keep it in ABLY_API_KEY on the server only.

Authenticate clients with a JWT

Browsers and mobile apps must never receive the API key. The server signs a short-lived JWT with the key secret; the SDK fetches it through authUrl (or authCallback) and renews it before it expires.

// server/ably-token.ts
import jwt from "jsonwebtoken";

const [keyName, keySecret] = process.env.ABLY_API_KEY!.split(":");

export function createAblyToken(userId: string): string {
  return jwt.sign(
    {
      "x-ably-clientId": userId,
      // capability is a JSON string: resource -> allowed operations
      "x-ably-capability": JSON.stringify({
        "orders:*": ["subscribe", "history"],
        [`notifications:${userId}`]: ["subscribe"],
        "support:*": ["publish", "subscribe", "presence", "history", "message-update-own"],
      }),