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HotLoop Edge Relay

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A poll-and-forward Sparkplug B edge node for a small industrial PC or a Pi.

Category: HotLoop

The Edge Relay polls devices with the same engine and drivers the HotLoop Gateway uses, and publishes every reading as Sparkplug B to an MQTT broker, where a Gateway picks it up. It reads and forwards, nothing else: no database, no web UI and no write path to your equipment.

What it does​

  • Polls devices over OPC UA, Modbus, MQTT and Sparkplug B, EtherNet/IP, S7comm, MTConnect or HTTP. A driver bug fixed in the Gateway is fixed here.
  • Buffers readings in a forward queue on its own volume when the link drops, so what it collected survives a pod restart.
  • Answers two read-only endpoints on port 8081, /healthz and /status, with counts and queue depth but no tag values, addresses or config.
  • Ships as an image of about 15 MB, against the Gateway's 34.

When to use it​

Use the Edge Relay where the Gateway doesn't run: a smaller cluster, a single-node edge box, or a Pi on a machine. It's a separate chart from the Gateway on purpose, because a relay is a different thing deployed in a different place, not a toggle on the Gateway's own deployment.

A Gateway registered with the relay through its fleet management API (/api/fleet, there's no Fleet screen) tracks it from its births and deaths, and can send it a rebirth, a restart or a new device file.

Running on EmberNet​

  • The Edge Relay deploys as a single instance per node.
  • It has no web interface, so there's nothing to open in EmberCORE. Devices and tags are declared in the chart's values and read once at start.
  • The relay and the Gateway both need to reach the same MQTT broker. Mosquitto is in the App Store if you don't have one.
Lock the broker down

Fleet commands travel over the broker, so anything that can publish to the relay's Sparkplug NCMD topic or to hotloop/edge-relay-config/# can restart it or push it a device file, exactly as the Gateway can. Give the broker an ACL that lets only the Gateway's credentials publish to those topics, and put TLS on it before you push a device file with passwords in it.

Licensing​

The Edge Relay is under the HotLoop Community License, the same as the Gateway. Any business use goes through EmberNet, where signing up is free and running HotLoop is free. See Using HotLoop in a business.

Learn more​

EmberNet packages and deploys this application; HotLoop is developed by HotLoop. Product names and logos are trademarks of their respective owners.