Allow defining the outside monitor URL via an environment variable

README.md

@@ -44,7 +44,7 @@ heartbeats:
 
 To add a new heartbeat, simply add it to the `heartbeats` section and then have the client responsible for it send `lvmbeat set <heartbeat_name>` every few seconds (but more frequently than `timeout`).
 
-The `outside_monitor` section defines the outside URL that the actor will call every `outside_monitor.interval`. `send_email_after` indicates how long the external monitor service will wait after it has not received a heartbeat to send an alert email.
+The `outside_monitor` section defines the outside URL that the actor will call every `outside_monitor.interval`. `send_email_after` indicates how long the external monitor service will wait after it has not received a heartbeat to send an alert email. The `url` value must be replaced with the URL of the external monitor service. The URL can also be defined by setting the environment variable `LVMBEAT_OUTSIDE_MONITOR_URL`.
 
 ### Status command
 

src/lvmbeat/actor.py

@@ -9,6 +9,7 @@
 from __future__ import annotations
 
 import asyncio
+import os
 from time import time
 
 from typing import Annotated, TypedDict
@@ -151,7 +152,11 @@ async def update(self):
     async def emit_outside(self):
         """Emits a heartbeat to the outside world."""
 
-        outside_url = config["outside_monitor"]["url"]
+        outside_url = os.getenv(
+            "LVMBEAT_OUTSIDE_MONITOR_URL",
+            config["outside_monitor"]["url"],
+        )
+
         if not outside_url:
             self.log.warning(
                 "No outside monitor URL defined. Will not emit "