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Process initializers

A process initializer runs when a sandbox process of your account starts, before it serves any of your code. It is the place for work which must exist in every process : a subscription to a message broker, a client kept for the life of the process, a warm cache.
Page API Info → Process Initializers : name, order, timeout in minutes, active, and the code.
Runs In every sandbox process, when it starts ; the active initializers in the order given, one after the other.
Code async function main(g: T.IAMGlobal), the same g as a custom API.
Test Test API runs it on the API testing page.
Subscribe to a topic and write the messages
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import * as T from 'types';
import * as mqtt from 'mqtt';   // added on the Sandbox Settings page

async function main(g: T.IAMGlobal) {
    const client = mqtt.connect(await g.sys.system.getSecret('mqtt.url'));
    client.on('message', async (topic, payload) => {
        await g.sys.db.saveSingleOrMultiple({ instance: 'mongodb', database: 'shop', collection: 'telemetry', saveData: { topic, payload: payload.toString(), at: new Date() } });
    });
    client.subscribe('shop/#');
    g.shared.mqtt = client;   // reachable by the code of this process
}
module.exports = main;
  • Other code runs on an action : an HTTP call, a schedule, an event. An initializer runs on its own, once per process, so keep it light and idempotent.
  • The number of sandbox processes is set on the Sandbox Settings page : each one runs the initializers.