Merge pull request #37 from leighmetzroth/jitter

Add jitter to delay the start of the first check

Author: KodrAus

src/Seq.Input.HealthCheck/HealthCheckInput.cs

@@ -15,6 +15,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Net.Http;
 using Seq.Apps;
 using Seq.Input.HealthCheck.Data;
@@ -88,7 +89,8 @@ public void Start(TextWriter inputWriter)
             extractor = new JsonDataExtractor(DataExtractionExpression);
 
         var targetUrls = TargetUrl.Split(new[] {'\r', '\n'}, StringSplitOptions.RemoveEmptyEntries);
-        foreach (var targetUrl in targetUrls)
+
+        foreach (var (targetUrl, ix) in targetUrls.Select((t, i) => (t, i)))
         {
             var healthCheck = new HttpHealthCheck(
                 _httpClient,
@@ -99,9 +101,14 @@ public void Start(TextWriter inputWriter)
                 BypassHttpCaching,
                 FollowRedirects);
 
+            var delayStart = targetUrls.Length <= 1
+                ? TimeSpan.Zero
+                : TimeSpan.FromMilliseconds(((IntervalSeconds * 1000.0) / targetUrls.Length) * ix);
+
             _healthCheckTasks.Add(new HealthCheckTask(
                 healthCheck,
                 TimeSpan.FromSeconds(IntervalSeconds),
+                delayStart,
                 reporter,
                 Log));
         }
@@ -120,4 +127,4 @@ public void Dispose()
 
         _httpClient?.Dispose();
     }
-}
+}

src/Seq.Input.HealthCheck/HealthCheckTask.cs

@@ -24,23 +24,26 @@ class HealthCheckTask : IDisposable
     readonly CancellationTokenSource _cancel = new();
     readonly Task _healthCheckTask;
 
-    public HealthCheckTask(HttpHealthCheck healthCheck, TimeSpan interval, HealthCheckReporter reporter, ILogger diagnosticLog)
+    public HealthCheckTask(HttpHealthCheck healthCheck, TimeSpan interval, TimeSpan delayStart, HealthCheckReporter reporter, ILogger diagnosticLog)
     {
         if (healthCheck == null) throw new ArgumentNullException(nameof(healthCheck));
         if (reporter == null) throw new ArgumentNullException(nameof(reporter));
 
-        _healthCheckTask = Task.Run(() => Run(healthCheck, interval, reporter, diagnosticLog, _cancel.Token), _cancel.Token);
+        _healthCheckTask = Task.Run(() => Run(healthCheck, interval, delayStart, reporter, diagnosticLog, _cancel.Token), _cancel.Token);
     }
 
     static async Task Run(
         HttpHealthCheck healthCheck,
-        TimeSpan interval, 
-        HealthCheckReporter reporter, 
+        TimeSpan interval,
+        TimeSpan delayStart,
+        HealthCheckReporter reporter,
         ILogger diagnosticLog,
         CancellationToken cancel)
     {
         try
         {
+            if (delayStart > TimeSpan.Zero) await Task.Delay(delayStart, cancel);
+
             while (!cancel.IsCancellationRequested)
             {
                 var result = await healthCheck.CheckNow(cancel);
@@ -74,4 +77,4 @@ public void Dispose()
         _cancel.Dispose();
         _healthCheckTask.Dispose();
     }
-}
+}