diff --git a/prom.md b/prom.md
new file mode 100644
index 0000000..47ae230
--- /dev/null
+++ b/prom.md
@@ -0,0 +1,59 @@
+# Prometheus exporter
+
+The goal of this version is to offer a few basic metrics for
+initial testing. The set of supported metrics can be extended.
+
+The current implementation is
+[unconventional](https://prometheus.io/docs/instrumenting/writing_exporters)
+in that it creates new metrics each time but does not register a
+custom collector. Reasons are that the exporter should
+[clear out metrics](https://github.com/prometheus/client_python/issues/182)
+for closed connections but that `prom-client`
+[does not yet support](https://github.com/siimon/prom-client/issues/241)
+custom collectors.
+
+This version has been ported from an earlier Python version that was not part
+of `multiparty-meeting` but connected as an interactive client.
+
+## Configuration
+
+| `.env` | description |
+|--------|-------|
+| `DEBUG` | e.g. `*WARN*,*ERROR*,*:prom` for debugging |
+| `PROM_DEIDENTIFY` | if set, deidentify IP addresses |
+| `PROM_NUMERIC` | if set, show numerical IP addresses |
+| `PROM_PORT` | if set, enable exporter on this port |
+| `PROM_QUIET` | if set, include fewer labels |
+
+## License
+
+MIT License (without copyright notice)
+
+## Metrics
+
+| metric | value |
+|--------|-------|
+| `edumeet_peers`| |
+| `edumeet_rooms`| |
+| `mediasoup_consumer_byte_count_bytes`| [`byteCount`](https://mediasoup.org/documentation/v3/mediasoup/rtc-statistics/#Consumer-Statistics) |
+| `mediasoup_consumer_score`| [`score`](https://mediasoup.org/documentation/v3/mediasoup/rtc-statistics/#Consumer-Statistics) |
+| `mediasoup_producer_byte_count_bytes`| [`byteCount`](https://mediasoup.org/documentation/v3/mediasoup/rtc-statistics/#Producer-Statistics) |
+| `mediasoup_producer_score`| [`score`](https://mediasoup.org/documentation/v3/mediasoup/rtc-statistics/#Producer-Statistics) |
+
+## Architecture
+
+```
++-----------+      +---------------------------------------------+
+| workers   |      | server                    observer API      |
+|           | sock |                    +------o------+----o-----+
+|           +------+                    | int. server | exporter |
+|           |      |                    |             |          |
+| mediasoup |      | express  socket.io |     net     | express  |
++-----+-----+      +----+---------+-----+-----+-------+-----+----+
+      ^ min-max         ^ 443     ^ 443       ^ sock        ^ PROM_PORT
+      | RTP             | HTTPS   | ws        |             | HTTP
+      |                 |         |           |             |
+      |               +-+---------+-+  +------+------+  +---+--------+
+      +---------------+     app     |  | int. client |  | Prometheus |
+                      +-------------+  +-------------+  +------------+
+```
diff --git a/server/lib/promExporter.js b/server/lib/promExporter.js
new file mode 100644
index 0000000..ccb2562
--- /dev/null
+++ b/server/lib/promExporter.js
@@ -0,0 +1,238 @@
+const { Resolver } = require('dns').promises;
+const express = require('express');
+const mediasoup = require('mediasoup');
+const prom = require('prom-client');
+
+const Logger = require('./Logger');
+const Peer = require('./Peer');
+const Room = require('./Room');
+
+const logger = new Logger('prom');
+const resolver = new Resolver();
+
+const workers = new Map();
+
+const label_names = [
+  'pid', 'room_id', 'peer_id', 'display_name', 'user_agent', 'transport_id',
+  'proto', 'local_addr', 'remote_addr', 'id', 'kind', 'codec', 'type'
+];
+
+const metadata = {
+  'byteCount': { metric_type: prom.Counter, unit: 'bytes' },
+  'score': { metric_type: prom.Gauge }
+}
+
+common_labels = function(both, fn) {
+  for (let [room_id, room] of rooms) {
+    for (let [peer_id, peer] of peers) {
+        if (fn(peer)) {
+          let display_name = peer._displayName;
+
+          let user_agent = peer._socket.client.request.headers['user-agent'];
+          let kind = both.kind;
+          let codec = both.rtpParameters.codecs[0].mimeType.split('/')[1];
+          return { room_id, peer_id, display_name, user_agent, kind, codec };
+        }
+     }
+  }
+  throw new Error('cannot find generic labels');
+}
+
+set_value = function(key, m, labels, v) {
+  logger.debug(`set_value key=${key} v=${v}`);
+  switch (metadata[key].metric_type) {
+  case prom.Counter:
+    m.inc(labels, v);
+    break;
+  case prom.Gauge:
+    m.set(labels, v);
+    break;
+  default:
+    throw new Error(`unexpected metric: ${metric}`);
+  }
+}
+
+
+addr = async function(ip, port) {
+  if ('PROM_DEIDENTIFY' in process.env) {
+    let a = ip.split('.')
+    for (let i = 0; i < a.length - 2; i++) {
+      a[i] = 'xx';
+    }
+    return a.join('.');
+  }
+  else if ('PROM_NUMERIC' in process.env) {
+    return ip;
+  }
+  else {
+    try {
+      let a = await resolver.reverse(ip);
+      ip = a[0];
+    }
+    catch (err) {
+      logger.error(`reverse DNS query failed: ${ip} ${err.code}`);
+    }
+    return `${ip}:${port}`;
+  }
+}
+
+quiet = function(s) {
+  return 'PROM_QUIET' in process.env ? '' : s;
+}
+
+collect = async function(registry, rooms, peers) {
+
+  metrics = function(subsystem) {
+    let namespace = 'mediasoup';
+    let metrics = new Map();
+    for (let key in metadata) {
+      value = metadata[key];
+      let name  = key.split(/(?=[A-Z])/).join('_').toLowerCase();
+      let unit = value.unit;
+      let metric_type = value.metric_type;
+      let s = `${namespace}_${subsystem}_${name}`;
+      if (unit) {
+        s += `_${unit}`;
+      }
+      m = new metric_type({name: s, help: `${subsystem}.${key}`,
+        labelNames: label_names, registers: [registry]});
+      metrics.set(key, m);
+    }
+    return metrics;
+  }
+
+  logger.debug('collect');
+  const m_rooms = new prom.Gauge({name: 'edumeet_rooms', help: '#rooms',
+    registers: [registry]});
+  m_rooms.set(rooms.size);
+  const m_peers = new prom.Gauge({name: 'edumeet_peers', help: '#peers',
+    labelNames: ['room_id'], registers: [registry]});
+  for (let [room_id, room] of rooms) {
+    m_peers.labels(room_id).set(Object.keys(room._peers).length);
+  }
+
+  const m_consumer = metrics('consumer');
+  const m_producer = metrics('producer');
+  for (let [pid, worker] of workers) {
+    logger.debug(`visiting worker ${pid}`);
+    for (let router of worker._routers) {
+      logger.debug(`visiting router ${router.id}`);
+      for (let [transport_id, transport] of router._transports) {
+        logger.debug(`visiting transport ${transport_id}`);
+        let transport_j = await transport.dump();
+        if (transport_j.iceState != 'completed') {
+          logger.debug(`skipping transport ${transport_id}}: ${transport_j.iceState}`);
+          continue;
+        }
+        let ice_selected_tuple = transport_j.iceSelectedTuple;
+        let proto = ice_selected_tuple.protocol
+        let local_addr = await addr(ice_selected_tuple.localIp,
+          ice_selected_tuple.localPort);
+        let remote_addr = await addr(ice_selected_tuple.remoteIp,
+          ice_selected_tuple.remotePort);
+        for (let [producer_id, producer] of transport._producers) {
+          logger.debug(`visiting producer ${producer_id}`);
+          let { room_id, peer_id, display_name, user_agent, kind, codec } = 
+            common_labels(producer, peer => peer._producers.has(producer_id));
+          let a = await producer.getStats();
+          for (let x of a) {
+            let type = x.type;
+            let labels = {
+             'pid': pid,
+             'room_id': room_id,
+             'peer_id': peer_id,
+             'display_name': display_name,
+             'user_agent': user_agent,
+             'transport_id': quiet(transport_id),
+             'proto': proto,
+             'local_addr': local_addr,
+             'remote_addr': remote_addr,
+             'id': quiet(producer_id),
+             'kind': kind,
+             'codec': codec,
+             'type': type
+            }
+            for (let [key, m] of m_producer) {
+              set_value(key, m, labels, x[key]);
+            }
+          }
+        }
+        for (let [consumer_id, consumer] of transport._consumers) {
+          logger.debug(`visiting consumer ${consumer_id}`);
+          let { room_id, peer_id, display_name, user_agent, kind, codec } = 
+            common_labels(consumer, peer => peer._consumers.has(consumer_id));
+          let a = await consumer.getStats();
+          for (let x of a) {
+            if (x.type == 'inbound-rtp') {
+              continue;
+            }
+            let type = x.type;
+            let labels = {
+             'pid': pid,
+             'room_id': room_id,
+             'peer_id': peer_id,
+             'display_name': display_name,
+             'user_agent': user_agent,
+             'transport_id': quiet(transport_id),
+             'proto': proto,
+             'local_addr': local_addr,
+             'remote_addr': remote_addr,
+             'id': quiet(consumer_id),
+             'kind': kind,
+             'codec': codec,
+             'type': type
+            }
+            for (let [key, m] of m_consumer) {
+              set_value(key, m, labels, x[key]);
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
+module.exports = async function(rooms, peers) {
+  try {
+    logger.debug(`PROM_DEIDENTIFY=${process.env.PROM_DEIDENTIFY}`);
+    logger.debug(`PROM_NUMERIC=${process.env.PROM_NUMERIC}`);
+    logger.debug(`PROM_PORT=${process.env.PROM_PORT}`);
+    logger.debug(`PROM_QUIET=${process.env.PROM_QUIET}`);
+    let s_port = process.env.PROM_PORT;
+    if (!s_port) {
+      logger.info('exporter disabled');
+    }
+    else {
+      let n_port = Number(s_port);
+      if (Number.isNaN(n_port)) {
+        throw new TypeError(`PROM_PORT has illegal value: ${s_port}`);
+      }
+
+      mediasoup.observer.on('newworker', worker => {
+        logger.debug(`observing newworker ${worker.pid} #${workers.size}`);
+        workers.set(worker.pid, worker);
+        worker.observer.on('close', () => {
+          logger.debug(`observing close worker ${worker.pid} #${workers.size - 1}`);
+          workers.delete(worker.pid);
+        });
+      });
+
+      let app = express();
+      app.get('/', async (req, res) => {
+        logger.debug(`GET ${req.originalUrl}`);
+        let registry = new prom.Registry();
+        await collect(registry, rooms, peers);
+        res.set('Content-Type', registry.contentType);
+        let data = registry.metrics();
+        res.end(data);
+      });
+      let server = app.listen(n_port, () => {
+        address = server.address();
+        logger.info(`listening ${address.address}:${address.port}`);
+      });
+    }
+  }
+  catch (err) {
+    logger.error(err);
+  }
+}
diff --git a/server/package.json b/server/package.json
index d8b314d..d156a62 100644
--- a/server/package.json
+++ b/server/package.json
@@ -31,6 +31,7 @@
 		"passport": "^0.4.0",
 		"passport-lti": "0.0.7",
 		"pidusage": "^2.0.17",
+		"prom-client": ">=12.0.0",
 		"redis": "^2.8.0",
 		"socket.io": "^2.3.0",
 		"spdy": "^4.0.1",
diff --git a/server/server.js b/server/server.js
index 70cb5bc..9253bec 100755
--- a/server/server.js
+++ b/server/server.js
@@ -34,6 +34,7 @@ const expressSession = require('express-session');
 const RedisStore = require('connect-redis')(expressSession);
 const sharedSession = require('express-socket.io-session');
 const interactiveServer = require('./lib/interactiveServer');
+const promExporter = require('./lib/promExporter');
 
 /* eslint-disable no-console */
 console.log('- process.env.DEBUG:', process.env.DEBUG);
@@ -132,6 +133,9 @@ async function run()
 	// Open the interactive server.
 	await interactiveServer(rooms, peers);
 
+        // start Prometheus exporter
+        await promExporter(rooms, peers);
+
 	if (typeof(config.auth) === 'undefined')
 	{
 		logger.warn('Auth is not configured properly!');