Impossible to reset the metrics in cluster mode

[oliviermarlec]

I implemented a counter metric in a Node JS http server. I have one master and eight workers so I use prom-client with the cluster module using the AggregatorRegistry class:

const { AggregatorRegistry } = require('prom-client');
const aggregatorRegistry = new AggregatorRegistry();

The collection of all metrics works properly with the following function I implemented:

async function sendMetrics(request, response) {
    try {
        const metrics = await aggregatorRegistry.clusterMetrics();
        response.writeHead(200, { 'Content-Type': aggregatorRegistry.contentType });
		response.end(metrics);
    } catch (ex) {
        response.writeHead(500, { 'Content-Type': aggregatorRegistry.contentType });
        response.end(ex.message);
    }
}

But the reset of the metrics doesn't work, here is function I defined for that:

async function flushMetrics(request, response) {
    try {
        await aggregatorRegistry.resetMetrics();
        response.writeHead(200, { 'Content-Type': aggregatorRegistry.contentType });
        response.end('OK\n');
    } catch (ex) {
        response.writeHead(500, { 'Content-Type': aggregatorRegistry.contentType });
        response.end(ex.message);
    }
}

After the call of flushMetrics() the metrics are unchanged.
Any idea ?

[zbjornson]

That's indeed not supported. The maintainers of Prometheus said that there are very few scenarios when users should use reset(), though: see #179, #236, #402, ...

Given that info, do you actually need support for this?