[AETHER-3071] Export num configured and reachable devices to Prometheus

Change-Id: I8cf178e6596460433f3b82c85e3d311e6f96f032
diff --git a/app.py b/app.py
index cc85ce4..3adb9dd 100644
--- a/app.py
+++ b/app.py
@@ -8,7 +8,6 @@
 import time
 
 from flask import Flask, request
-from flask_restful import Resource, Api
 import logging as log
 from argparse import ArgumentParser, SUPPRESS
 import threading
@@ -19,40 +18,39 @@
 import device
 
 app = Flask(__name__)
-api = Api(app)
 
 devices = {} # dict imsi:device
 lock = threading.Lock()
 
 
-class Devices(Resource):
-    def get(self):
-        global devices, lock
-        with lock:
-            all = {}
-            for _, device in devices.items():
-                all[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
-        return all
+@app.route("/devices")
+def get_devices():
+    global devices, lock
+    with lock:
+        all = {}
+        for _, device in devices.items():
+            all[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
+    return all
 
-class ReachableDevices(Resource):
-    def get(self):
-        global devices, lock
-        with lock:
-            reachable = {}
-            for _, device in devices.items():
-                if device.reachable is True:
-                    reachable[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
-        return reachable
+@app.route("/devices/reachable")
+def get_devices_reachable():
+    global devices, lock
+    with lock:
+        reachable = {}
+        for _, device in devices.items():
+            if device.reachable is True:
+                reachable[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
+    return reachable
 
-class UnreachableDevices(Resource):
-    def get(self):
-        global devices, lock
-        with lock:
-            unreachable = {}
-            for _, device in devices.items():
-                if device.reachable is False:
-                    unreachable[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
-        return unreachable
+@app.route("/devices/unreachable")
+def get_devices_unreachable():
+    global devices, lock
+    with lock:
+        unreachable = {}
+        for _, device in devices.items():
+            if device.reachable is False:
+                unreachable[device.imsi_id] = {'ip':device.ip, 'imsi':device.imsi, 'last_reachable':'{:%Y-%m-%d %H:%M:%S}'.format(device.last_reachable)}
+    return unreachable
 
 
 
@@ -116,10 +114,6 @@
         datefmt='%Y-%m-%d %H:%M:%S',
         stream=sys.stdout)
 
-    api.add_resource(Devices, '/devices')
-    api.add_resource(ReachableDevices, '/devices/reachable')
-    api.add_resource(UnreachableDevices, '/devices/unreachable')
-
     log.info("Starting network-diag-app...")
 
     args = build_argparser().parse_args()
diff --git a/exporter.py b/exporter.py
new file mode 100644
index 0000000..bb8c2d0
--- /dev/null
+++ b/exporter.py
@@ -0,0 +1,42 @@
+"""network-diag-app exporter"""
+
+import os
+import time
+from prometheus_client import start_http_server, Gauge
+import requests
+import json
+
+class Metrics:
+    def __init__(self, app_port=3333, polling_interval_seconds=5):
+        self.app_port = app_port
+        self.polling_interval_seconds = polling_interval_seconds
+
+        self.num_configured_devices = Gauge("num_configured_devices", "Number of configured devices")
+        self.num_configured_devices = Gauge("num_reachable_devices", "Number of reachable devices")
+
+    def run_metrics_loop(self):
+        while True:
+            self.fetch()
+            time.sleep(self.polling_interval_seconds)
+
+    def fetch(self):
+        resp = requests.get(url=f"http://localhost:{self.app_port}/devices")
+        self.num_configured_devices = len(json.loads(resp.text))
+
+        resp = requests.get(url=f"http://localhost:{self.app_port}/devices/reachable")
+        self.num_configured_devices = len(json.loads(resp.text))
+
+def main():
+    polling_interval_seconds = int(os.getenv("POLLING_INTERVAL_SECONDS", "5"))
+    app_port = int(os.getenv("APP_PORT", "3333"))
+    exporter_port = int(os.getenv("EXPORTER_PORT", "4444"))
+
+    app_metrics = Metrics(
+        app_port=app_port,
+        polling_interval_seconds=polling_interval_seconds
+    )
+    start_http_server(exporter_port)
+    app_metrics.run_metrics_loop()
+
+if __name__ == "__main__":
+    main()
diff --git a/requirements.txt b/requirements.txt
index c51d4df..06b8f1c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,6 +10,7 @@
 itsdangerous==2.0.1
 Jinja2==3.0.3
 MarkupSafe==2.0.1
+prometheus-client==0.13.1
 pyaml==21.10.1
 pytz==2021.3
 PyYAML==6.0