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| 1 | +--- |
| 2 | +title: 'Cross-node bus: finally, pub/sub that actually crosses nodes' |
| 3 | +author: [gallayl] |
| 4 | +tags: |
| 5 | + [ |
| 6 | + 'Architecture', |
| 7 | + 'distributed-systems', |
| 8 | + 'redis', |
| 9 | + 'entity-sync', |
| 10 | + 'rest-service', |
| 11 | + 'identity', |
| 12 | + 'cross-node-bus', |
| 13 | + ] |
| 14 | +date: '2026-06-09T12:00:00.000Z' |
| 15 | +draft: false |
| 16 | +image: img/021-cross-node-bus.png |
| 17 | +excerpt: 'FuryStack now ships a real cross-node event bus and a Redis Streams adapter, so identity invalidation and entity sync finally work across pods instead of just within one lonely process.' |
| 18 | +--- |
| 19 | + |
| 20 | +If your FuryStack app has ever been deployed as more than one pod, you already know the classic bug: |
| 21 | + |
| 22 | +- user logs out on Pod A |
| 23 | +- Pod B keeps serving stale identity until the cache TTL expires |
| 24 | +- the whole system acts like the other nodes are imaginary friends |
| 25 | + |
| 26 | +That illusion is over. |
| 27 | + |
| 28 | +## What shipped |
| 29 | + |
| 30 | +The new release adds a tiny public bus abstraction in `@furystack/cross-node-bus` plus a real Redis Streams adapter in `@furystack/redis-cross-node-bus`. |
| 31 | + |
| 32 | +That means the framework now has one shared, transport-agnostic primitive for: |
| 33 | + |
| 34 | +- identity events (`IdentityEventBus`) |
| 35 | +- entity change broadcasts (`EntityChangeBus`) |
| 36 | +- app-defined typed facades over the bus |
| 37 | + |
| 38 | +The implementation is intentionally straightforward, because a distributed event bus should be predictable and reliable before it tries to be clever. |
| 39 | + |
| 40 | +## Why this matters |
| 41 | + |
| 42 | +Before this, FuryStack's internal `EventHub` and cache invalidations were strictly process-local. The app could run on N pods behind a load balancer, and every cross-cutting channel still behaved like a single-node app. |
| 43 | + |
| 44 | +The new bus changes that: |
| 45 | + |
| 46 | +- logout and session invalidation events now propagate across nodes |
| 47 | +- entity change notifications now fan out from one write node to every sibling |
| 48 | +- adapters can assign sequence ids, support replay, and let reconnecting consumers catch up without guessing |
| 49 | + |
| 50 | +In other words: the system now treats the fleet as one cooperative actor instead of N independent silos. |
| 51 | + |
| 52 | +## The simple API that makes this work |
| 53 | + |
| 54 | +The core package defines one shared token: `CrossNodeBus`. |
| 55 | + |
| 56 | +That token exposes a small interface: |
| 57 | + |
| 58 | +- `publish(topic, payload)` |
| 59 | +- `subscribe(topic, handler)` |
| 60 | +- `subscribeRemoteOnly(topic, handler)` |
| 61 | +- `subscribeForeign(prefix, topic, handler)` |
| 62 | +- `replay(topic, fromSeq)` |
| 63 | + |
| 64 | +And yes, it also exposes a stable `nodeId` and a capability descriptor so the framework can refuse to start if the bound adapter does not support the features it needs. |
| 65 | + |
| 66 | +That last bit is important. `EntityChangeBus` requires `replay` and `assignsSequence`, and we now fail loudly at startup instead of letting a non-replaying adapter serve stale data forever. |
| 67 | + |
| 68 | +## What the packages do |
| 69 | + |
| 70 | +### `@furystack/cross-node-bus` |
| 71 | + |
| 72 | +This is the abstraction. It includes: |
| 73 | + |
| 74 | +- the `CrossNodeBus` token |
| 75 | +- `InProcessCrossNodeBus` default factory for single-node apps |
| 76 | +- a shared `BusMessage` envelope with `originId`, `emittedAt`, optional `seq`, and version pinning |
| 77 | +- a lightweight in-process replay ring buffer for reconnecting subscribers |
| 78 | +- a testing harness for multi-instance in-process simulations |
| 79 | + |
| 80 | +The default adapter is intentionally unexciting. If you do not bind a transport adapter, the bus still works in one process exactly like before. |
| 81 | + |
| 82 | +### `@furystack/redis-cross-node-bus` |
| 83 | + |
| 84 | +This is the production-grade adapter that actually talks to Redis Streams. |
| 85 | + |
| 86 | +It supports: |
| 87 | + |
| 88 | +- persistence |
| 89 | +- server-assigned sequence ids |
| 90 | +- replay from an arbitrary stream position |
| 91 | +- prefix-based multi-service isolation |
| 92 | +- explicit cross-prefix subscription via `subscribeForeign` |
| 93 | + |
| 94 | +The Redis adapter also duplicates the Redis client for the read loop, so every subscriber can boot without requiring consumer groups or orphaned group state. |
| 95 | + |
| 96 | +## Identity and entity sync now live on the same shared bus |
| 97 | + |
| 98 | +The two framework facades that landed with this release are the ones where the difference is most visible: |
| 99 | + |
| 100 | +- `IdentityEventBus` in `@furystack/rest-service` now publishes logout/invalidation events to the bus and invalidates cached user resolution across nodes. |
| 101 | +- `EntityChangeBus` in `@furystack/entity-sync-service` now publishes model-level deltas on the bus and uses replay to restore reconnecting clients. |
| 102 | + |
| 103 | +That means a logout on one node invalidates the same cache entry everywhere, and a model update on one node is no longer invisible to the rest of the cluster. |
| 104 | + |
| 105 | +## What “cross-node” actually looks like |
| 106 | + |
| 107 | +The implementation is deliberately opinionated about one thing: the bus is a broadcast notification layer, not a distributed state store. |
| 108 | + |
| 109 | +So: |
| 110 | + |
| 111 | +- the bus carries events, not entire object graphs |
| 112 | +- receivers still re-read their local store when they need the canonical state |
| 113 | +- duplicates are fine, because the system is already designed for them |
| 114 | +- ordering is only guaranteed per-publisher, not globally across the fleet |
| 115 | + |
| 116 | +That is the practical design FuryStack needs right now: a broadcast notification layer, not a distributed state machine. |
| 117 | + |
| 118 | +## How apps should use it |
| 119 | + |
| 120 | +App authors do not need to use low-level Redis or wire-format details. The recommended pattern is: |
| 121 | + |
| 122 | +- bind `CrossNodeBus` to a transport adapter |
| 123 | +- define a typed facade over the bus |
| 124 | +- publish typed domain events on that facade |
| 125 | +- subscribe using the facade's local event API |
| 126 | + |
| 127 | +This is the same pattern the framework facades already use, and it means custom app buses can be built with the same DX as `EventHub<T>` while still getting cross-node delivery. |
| 128 | + |
| 129 | +Example sketch: |
| 130 | + |
| 131 | +```ts |
| 132 | +const AppEventBus = defineService({ |
| 133 | + name: 'my-app/AppEventBus', |
| 134 | + lifetime: 'singleton', |
| 135 | + factory: ({ inject, onDispose }) => { |
| 136 | + const bus = inject(CrossNodeBus); |
| 137 | + const local = new EventHub<{ event: AppEvent }>(); |
| 138 | + |
| 139 | + const handle = bus.subscribe('app/events', message => { |
| 140 | + local.emit('event', message.payload as AppEvent); |
| 141 | + }); |
| 142 | + |
| 143 | + onDispose(() => handle[Symbol.dispose]()); |
| 144 | + |
| 145 | + return { |
| 146 | + subscribe: (handler: (e: AppEvent) => void) => local.subscribe('event', handler), |
| 147 | + publish: (event: AppEvent) => bus.publish('app/events', event), |
| 148 | + }; |
| 149 | + }, |
| 150 | +}); |
| 151 | +``` |
| 152 | + |
| 153 | +This release ships that pattern in the framework and makes it the recommended extension point for app-defined coordination. |
| 154 | + |
| 155 | +## So what changed for release users? |
| 156 | + |
| 157 | +If you are already on FuryStack 2026, the new bus means: |
| 158 | + |
| 159 | +- single-node apps keep working as before |
| 160 | +- multi-node apps can bind `@furystack/redis-cross-node-bus` |
| 161 | +- identity invalidation becomes fleet-wide instead of pod-local |
| 162 | +- entity sync uses replay and sequence numbers instead of fragile local changelogs |
| 163 | + |
| 164 | +If your app needs cross-service isolation, `topicPrefix` gives each service its own wire namespace, and `subscribeForeign` makes cross-service eavesdrop explicit. |
| 165 | + |
| 166 | +## Final note |
| 167 | + |
| 168 | +This is the kind of feature that is boring to write and exciting to use. |
| 169 | + |
| 170 | +You do not need a new framework API for every cross-node event you want to publish. You only need a small shared bus, a typed facade, and a shipping-quality adapter. |
| 171 | + |
| 172 | +`@furystack/cross-node-bus` is that shared bus. `@furystack/redis-cross-node-bus` is the adapter that makes it real. |
| 173 | + |
| 174 | +If your app runs on more than one pod, go try it. If your app does not, congrats — no upgrade urgency, but the package still ships with a really clean in-process default. |
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