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Edge Gateway

Modbus to HTTP / REST

A Modbus device, posted to an HTTP endpoint one message at a time or as JSON arrays, with the authentication the API expects.

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The data flow

SOURCE TO AN HTTP ENDPOINTModbus devicePLC · meter · driveEdge Gatewaythe runtime on your devicepolls · decodes · scalesbatches N messages per requestHTTP endpointPOST · PUT · PATCHURL + optional per-message pathAPI key, bearer or basic authretries with timeout

The same JSON envelope as MQTT, delivered by an HTTP request instead of a publish. A failed request is retried with a back-off; with a Store & forward node in front, messages wait on disk while the endpoint is down.

In the editor

Edge LogicPump house✓ Saved · v3DeployFilter nodes…PLC & INDUSTRIALModbusSiemens S7Allen-Bradley (CIP)…TRANSFORMSScaleDeadbandExpression…LOGIC & ROUTINGCondition / RouteJoinInject / TriggerOUTPUTMQTT outHTTP outSQL out…GATEWAYModbus converterMain meterModbus · 192.168.1.20every 1 s · 6 tagsReshapeJSON templateCloud APIHTTP outPOST · bearer tokenCloud APIURLhttps://api.example.com/ingestPATH PER MESSAGE/{device}/{tag}METHODPOSTAUTHENTICATIONBearer tokenMESSAGES PER REQUEST1
A JSON template on the wire gives the API the shape it wants; HTTP out posts it.

HTTP out posts to a URL. Path per message is appended to it, with {device} and {tag} substituted, so an API that wants one resource per tag gets it; left empty, everything goes to the URL itself. Headers are name and value pairs. Authentication names the scheme; Messages per request above 1 sends a JSON array per request, collected for Batch wait milliseconds.

The API key, token or password is never in the design. After the install, on the device: modbuslogic-edge secrets set <destination-id> token. The runtime keeps it encrypted there; a design or a download can be shared without carrying it. The destination id is in the log line the runtime prints for the destination, and in project.json under the data directory.

A JSON template node before the output rewrites the body: {"t":"{{ts}}","point":"{{device}}/{{tag}}","v":{{value}}}. The placeholders are in Logic and routing nodes.

Test it with the Modbus Simulator

You do not need the PLC to try this flow. The Modbus Simulator answers as a Modbus slave on your own PC, with registers that move, so the whole path from polling to the output can be watched before any hardware is involved.

  1. Start the Simulator and add a slave: Modbus TCP, bind host set to this PC's LAN address (the prefilled one), port 1502, unit ID 1. Add a few holding registers, say 40001–40010 as FLOAT32 or INT16 in random mode so the values change, and press Start.
  2. In the editor, set the source node's host to that address, port 1502, unit ID 1, and the same addresses and data types. Poll interval 1s is fine.
  3. Deploy the design to a device on the same network, or to this very PC: the Edge Gateway Console installs on a laptop as readily as on an edge computer, and the gateway polls the Simulator over the LAN.
  4. The Simulator's request log shows the gateway's reads arriving: function code 03, the start address and quantity, once per poll interval. Neighbouring registers arrive as one read.
  5. Point the URL at anything that logs requests: a local HTTP server, a request-bin service, or your own API in development. Each poll that changes a value produces one request, with the body shown above.
THE TEST BENCHModbus Simulatora slave on your PC · port 1502registers in random moderequest log shows each readEdge Gatewaythe runtime on your devicepolls every secondthe live view shows valuesThe outputon the same PC or elsewhere

Registers in fixed mode make a deadband or a condition easy to exercise: change a value by hand and watch what is, and is not, published. A register set to a value the Simulator refuses (uncheck Fill unmapped and read an address that is not there) shows what a BAD quality looks like at the output. The Simulator's own page has the rest.

From design to device

THE SAME FOUR STEPS FOR EVERY FLOWValidateon the design pageInstallthe console on the deviceDevice codeentered on the design pageBundlegiven to the console
  1. Validate. On the design page, Run validation. The editor's rules, the tag document and the runtime binary itself check the design; every issue names its node. Details: Validating a design.
  2. Install. From the Devices panel download the installer for the device's platform (Windows x64, Linux x64 or Linux ARM64). Windows: extract and run Edge-Gateway-Console.exe from an administrator terminal. Linux (Debian, Ubuntu, Raspberry Pi OS): sudo dpkg -i the .deb, then sudo edge-gateway-console. It shows the device code. Details: Installing on the device.
  3. Device code. Enter it in the Devices panel, choose a trial or one of your purchased licences, and press Download activation bundle: one small zip with the design and a licence bound to that machine, sealed so only that machine can open it. Details: Downloading.
  4. Bundle. Give the zip to the console (drag it onto the program, pass its path, or put it beside the program and run it again; a USB stick is fine for a device without internet). It opens the bundle with its own code, installs the runtime as a service and starts it. The device never contacts the site. Details: Activation and the licence.

The console then opens the gateway's web view in a browser (on a device without a desktop it prints the address instead) and stays attached with the live view: devices up or down, values as they change, what was published, and the log.

  • The live view shows the endpoint as connected once a request has succeeded, with the count of sent and failed requests and the last error text when there is one.
  • Your endpoint receives the envelope, or the template's body, at the path per message.

Ctrl-C leaves the gateway running as a service. Run edge-gateway-console again at any time: it shows the service, the licence, every device and destination with what to check, the web view, and the live log. Running covers the data directory, secrets and the diagnostics.

Modbus to HTTP / REST · Edge Gateway documentation | Modbus Logic