# Runtime Topology: 006 Messaging NATS Replacement

> For the complete documentation index, see [llms.txt](https://deploy-preview-472--lucky-concha-f3599f.netlify.app/llms.txt).

Parent state: `005-postgres-database-replacement`

## Entrypoints

*   Browser/UI ingress: `http://localhost:8080`
*   NATS client port (internal compose network): `4222`
*   NATS monitoring (optional local): `8222`
*   NATS websocket ingress path (proxied): `/nats-ws`

## Components

*   `nats-broker` replaces messaging role previously handled by `trade-feed`.
*   `trade-service` publishes `trades.new`.
*   `trade-processor` consumes `trades.new` and publishes account-scoped trade/position updates.
*   `web-front-end-angular` subscribes to account-scoped update subjects through `nats.ws`.

## Networking

*   Service-to-service messaging uses NATS TCP over compose network.
*   Browser real-time stream uses WebSocket upgrade through ingress path `/nats-ws`.
*   Existing REST routing through ingress remains unchanged.

## Startup / Health Order

*   `nats-broker` must be healthy before trade-service/trade-processor startup.
*   Frontend may start before broker, but stream subscriptions must retry until broker and websocket path are available.

## Source-of-Truth Files

*   `system/messaging-subject-map.md`
*   `system/docker-compose.nats.snippet.yaml`
*   `system/ingress-nginx.nats-ws.snippet.conf`