Prevent devices always being pinged at exactly the same time (#6133)

* Add availability lag of rand 10% from timeout

* Update availability.js

* Update utils.js

Co-authored-by: Koen Kanters <koenkanters94@gmail.com>

.dockerignore

@@ -3,6 +3,7 @@
 .git
 .github
 .gitignore
+.idea
 .npmrc
 .travis*
 .travis.yml
@@ -12,4 +13,4 @@ images
 node_modules
 scripts
 test
-update.sh
+update.sh

lib/extension/availability.js

@@ -14,6 +14,13 @@ const pingableEndDevices = [
 ];
 
 const Hours25 = 1000 * 60 * 60 * 25;
+const AvailabilityLagRatio = 0.1;
+
+
+function timeoutLag(timeout, ratio) {
+    const lag = timeout * ratio;
+    return Math.floor(Math.random() * Math.floor(lag));
+}
 
 /**
  * This extensions pings devices to check if they are online.
@@ -137,10 +144,11 @@ class Availability extends Extension {
     }
 
     setTimerPingable(device) {
+        const timeout = this.availability_timeout + timeoutLag(this.availability_timeout, AvailabilityLagRatio);
         clearTimeout(this.timers[device.ieeeAddr]);
         this.timers[device.ieeeAddr] = setTimeout(async () => {
             await this.handleIntervalPingable(device);
-        }, utils.secondsToMilliseconds(this.availability_timeout));
+        }, utils.secondsToMilliseconds(timeout));
     }
 
     async stop() {