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Use App Config and Global Config from inside your app

This article refers to Platform v3.1.0. The current Platform version is v3.2.0.

Overview​

A Barbara edge node exposes two JSON configuration channels to every workload:

  • App Config — JSON edited in the Config segment of the workload card; scoped to one workload.
  • Global Config — JSON edited in the Global Config card; shared by every workload on the node.

Both are surfaced inside the container as flat JSON files the app reads at runtime. Changes are picked up live, so you can push a new value from Panel and the app picks it up the next time it re-reads the file.

This article extends the MQTT app from the previous steps to publish messages that are driven by App Config and Global Config.

Video walkthrough

Watch this step on YouTube: Using App & Global Config in an Application.

Where the config lives inside the container​

ConfigPath inside the containerPanel surface
Global Config/appconfig/global.jsonGlobal Config card
App Config/appconfig/appconfig.jsonConfig segment of the workload card

No special compose syntax is required — Barbara mounts both files into every container automatically. Your app just reads JSON from those paths.

Practice — publish messages driven by config​

We will publish two MQTT messages every 5 seconds — one driven by Global Config, one by App Config.

1. Set Global Config​

In the Global Config card on the Node Details page, set:

{
  "message": "helloGlobal",
  "topic": "test/globalTopic"
}

2. Set App Config​

In the Config segment of the workload card for mqtt_client, set:

{
  "message": "helloLocal",
  "topic": "test/localTopic"
}

3. Read both configs from code​

Add two helpers to test.py and call them in a loop:

import json
import time


def publish_global_config():
    try:
        with open('/appconfig/global.json') as f:
            data = json.load(f)
        client.publish(data["topic"], data["message"])
        print(f"Published from Global Config: {data['message']} → {data['topic']}")
    except Exception as exc:
        print(f"Global config not available: {exc}")


def publish_app_config():
    try:
        with open('/appconfig/appconfig.json') as f:
            data = json.load(f)
        client.publish(data["topic"], data["message"])
        print(f"Published from App Config: {data['message']} → {data['topic']}")
    except Exception as exc:
        print(f"App config not available: {exc}")


while True:
    publish_global_config()
    publish_app_config()
    time.sleep(5)

4. Push a new version​

Zip the source, upload it to the App Library as a new version of mqtt_client, and update the workload from its card.

5. Watch the changes live​

Open MQTT Explorer (or any MQTT client) and connect to the Marketplace MQTT Broker. You should see messages on test/globalTopic and test/localTopic.

Now edit the App Config or the Global Config in Panel — the topic and the payload change on the next loop iteration without restarting the workload.

Summary​

App Config and Global Config are the right home for non-sensitive, frequently-changing parameters. They reach your app as plain JSON files at known paths and reload live. For sensitive material, use Secrets instead — and for the full reference of all five configuration mechanisms, see Application configuration types.