disable metrics publisher for custom containers (#4707)

Author: divyagandhisethi

src/WebJobs.Script.WebHost/NullMetricsPublisher.cs

@@ -3,17 +3,23 @@
 
 using System;
 using Microsoft.Azure.WebJobs.Script.WebHost.Metrics;
+using Microsoft.Extensions.Logging;
 
 namespace Microsoft.Azure.WebJobs.Script.WebHost
 {
     public class NullMetricsPublisher : IMetricsPublisher
     {
-        private static readonly Lazy<NullMetricsPublisher> _instance = new Lazy<NullMetricsPublisher>(new NullMetricsPublisher());
+        private readonly ILogger _logger;
 
-        public static NullMetricsPublisher Instance => _instance.Value;
+        public NullMetricsPublisher(ILogger<NullMetricsPublisher> logger)
+        {
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+            _logger.LogDebug("Initializing null metrics publisher");
+        }
 
         public void AddFunctionExecutionActivity(string functionName, string invocationId, int concurrency, string executionStage, bool success, long executionTimeSpan, DateTime utcNow)
         {
+            _logger.LogDebug("Ignoring function activity metric: {functionName} {invocationId} {concurrency} {executionStage} {success} {executionTimeSpan}", functionName, invocationId, concurrency, executionStage, success, executionTimeSpan);
         }
     }
 }

src/WebJobs.Script.WebHost/WebHostServiceCollectionExtensions.cs

@@ -173,7 +173,7 @@ private static void AddLinuxContainerServices(this IServiceCollection services)
             services.AddSingleton<IMetricsPublisher>(s =>
             {
                 var environment = s.GetService<IEnvironment>();
-                if (environment.IsLinuxContainerEnvironment())
+                if (environment.IsLinuxMetricsPublishingEnabled())
                 {
                     var logger = s.GetService<ILogger<LinuxContainerMetricsPublisher>>();
                     var standbyOptions = s.GetService<IOptionsMonitor<StandbyOptions>>();
@@ -182,7 +182,8 @@ private static void AddLinuxContainerServices(this IServiceCollection services)
                     return new LinuxContainerMetricsPublisher(environment, standbyOptions, logger, httpClient, hostNameProvider);
                 }
 
-                return NullMetricsPublisher.Instance;
+                var nullMetricsLogger = s.GetService<ILogger<NullMetricsPublisher>>();
+                return new NullMetricsPublisher(nullMetricsLogger);
             });
         }
     }

src/WebJobs.Script/Environment/EnvironmentExtensions.cs

@@ -28,6 +28,11 @@ public static bool IsLinuxContainerEnvironment(this IEnvironment environment)
             return !environment.IsAppServiceEnvironment() && !string.IsNullOrEmpty(environment.GetEnvironmentVariable(ContainerName));
         }
 
+        public static bool IsLinuxMetricsPublishingEnabled(this IEnvironment environment)
+        {
+            return environment.IsLinuxContainerEnvironment() && string.IsNullOrEmpty(environment.GetEnvironmentVariable(ContainerStartContext));
+        }
+
         public static bool IsLinuxAppServiceEnvironment(this IEnvironment environment)
         {
             return environment.IsAppServiceEnvironment() && !string.IsNullOrEmpty(environment.GetEnvironmentVariable(FunctionsLogsMountPath));