[Backport 7.x] Improve warning for transient product check failures

src/Elasticsearch.Net/Transport/Pipeline/ProductCheckStatus.cs

@@ -12,6 +12,7 @@ public enum ProductCheckStatus
 		NotChecked,
 		ValidProduct,
 		InvalidProduct,
-		UndeterminedProduct
+		UndeterminedProduct,
+		TransientFailure
 	}
 }

src/Elasticsearch.Net/Transport/Pipeline/RequestPipeline.cs

@@ -23,8 +23,13 @@ public class RequestPipeline : IRequestPipeline
 		private const string ExpectedTagLine = "You Know, for Search";
 		private const string NoNodesAttemptedMessage = "No nodes were attempted, this can happen when a node predicate does not match any nodes";
 
+		public const string ProductCheckTransientErrorWarning =
+			"The client is unable to verify that the server is Elasticsearch due to an unsuccessful product check call. "
+			+ "Some functionality may not be compatible if the server is running an unsupported product.";
+
 		public const string UndeterminedProductWarning =
-			"The client is unable to verify that the server is Elasticsearch due security privileges on the server side.";
+			"The client is unable to verify that the server is Elasticsearch due to security privileges on the server side. "
+			+ "Some functionality may not be compatible if the server is running an unsupported product.";
 
 		private static readonly Version MinVersion = new(6, 0, 0);
 		private static readonly Version Version7 = new(7, 0, 0);
@@ -255,7 +260,7 @@ public ElasticsearchClientException CreateClientException<TResponse>(
 		public void FirstPoolUsage(SemaphoreSlim semaphore)
 		{
 			// If sniffing has completed and the product check has run, we are done!
-			if (!FirstPoolUsageNeedsSniffing && _connectionPool.ProductCheckStatus != ProductCheckStatus.NotChecked)
+			if (!FirstPoolUsageNeedsSniffing && !RequiresProductCheck(_connectionPool.ProductCheckStatus))
 				return;
 
 			if (!semaphore.Wait(_settings.RequestTimeout.Add(_settings.RequestTimeout))) // Double the timeout to allow for product check delays
@@ -270,7 +275,7 @@ public void FirstPoolUsage(SemaphoreSlim semaphore)
 
 			try
 			{
-				if (_connectionPool.ProductCheckStatus == ProductCheckStatus.NotChecked)
+				if (RequiresProductCheck(_connectionPool.ProductCheckStatus))
 					using (Audit(ProductCheckOnStartup))
 					{
 						var nodes = _connectionPool.Nodes.ToArray(); // Isolated copy of nodes for the product check
@@ -282,8 +287,9 @@ public void FirstPoolUsage(SemaphoreSlim semaphore)
 						}
 						else
 							// We determine the product from the first node which successfully responds.
+							// If a node fails, we retry other available nodes until the request timeout is reached.
 							for (var i = 0;
-								i < nodes.Length && _connectionPool.ProductCheckStatus == ProductCheckStatus.NotChecked && !IsTakingTooLong;
+								i < nodes.Length && RequiresProductCheck(_connectionPool.ProductCheckStatus) && !IsTakingTooLong;
 								i++)
 								ProductCheck(nodes[i]);
 
@@ -311,7 +317,7 @@ public void FirstPoolUsage(SemaphoreSlim semaphore)
 		public async Task FirstPoolUsageAsync(SemaphoreSlim semaphore, CancellationToken cancellationToken)
 		{
 			// If sniffing has completed and the product check has run, we are done!
-			if (!FirstPoolUsageNeedsSniffing && _connectionPool.ProductCheckStatus != ProductCheckStatus.NotChecked)
+			if (!FirstPoolUsageNeedsSniffing && !RequiresProductCheck(_connectionPool.ProductCheckStatus))
 				return;
 
 			// TODO cancellationToken could throw here and will bubble out as OperationCancelledException
@@ -330,7 +336,7 @@ public async Task FirstPoolUsageAsync(SemaphoreSlim semaphore, CancellationToken
 
 			try
 			{
-				if (_connectionPool.ProductCheckStatus == ProductCheckStatus.NotChecked)
+				if (RequiresProductCheck(_connectionPool.ProductCheckStatus))
 					using (Audit(ProductCheckOnStartup))
 					{
 						var nodes = _connectionPool.Nodes.ToArray(); // Isolated copy of nodes for the product check
@@ -342,8 +348,9 @@ public async Task FirstPoolUsageAsync(SemaphoreSlim semaphore, CancellationToken
 						}
 						else
 							// We determine the product from the first node which successfully responds.
+							// If a node fails, we retry other available nodes until the request timeout is reached.
 							for (var i = 0;
-								i < nodes.Length && _connectionPool.ProductCheckStatus == ProductCheckStatus.NotChecked && !IsTakingTooLong;
+								i < nodes.Length && RequiresProductCheck(_connectionPool.ProductCheckStatus) && !IsTakingTooLong;
 								i++)
 								await ProductCheckAsync(nodes[i], cancellationToken).ConfigureAwait(false);
 
@@ -595,21 +602,37 @@ public void ThrowNoNodesAttempted(RequestData requestData, List<PipelineExceptio
 				throw new UnexpectedElasticsearchClientException(clientException, seenExceptions) { Request = requestData, AuditTrail = AuditTrail };
 		}
 
+		private static bool RequiresProductCheck(ProductCheckStatus status) =>
+			status is ProductCheckStatus.NotChecked or ProductCheckStatus.TransientFailure;
+
 		private TResponse PostCallElasticsearch<TResponse>(RequestData requestData, TResponse response,
 			Diagnostic<RequestData, IApiCallDetails> diagnostic, Auditable audit
 		)
 			where TResponse : class, IElasticsearchResponse, new()
 		{
-			// Add additional warning to debug information if the product could not be determined and may not be Elasticsearch
-			if (_connectionPool.ProductCheckStatus == ProductCheckStatus.UndeterminedProduct && response.ApiCall is ApiCallDetails callDetails)
-			{
-				Debug.WriteLine(UndeterminedProductWarning);
-				callDetails.BuildDebugInformationPrefix = sb =>
+			if (response.ApiCall is ApiCallDetails callDetails)
+				switch (_connectionPool.ProductCheckStatus)
 				{
-					sb.AppendLine("# Warnings:");
-					sb.AppendLine($"- {UndeterminedProductWarning}");
-				};
-			}
+					// Add additional warning to debug information if the product could not be determined and may not be Elasticsearch
+					case ProductCheckStatus.UndeterminedProduct:
+						Debug.WriteLine(UndeterminedProductWarning);
+						callDetails.BuildDebugInformationPrefix = sb =>
+						{
+							sb.AppendLine("# Warnings:");
+							sb.AppendLine($"- {UndeterminedProductWarning}");
+						};
+						break;
+
+					// Add additional warning to debug information if the product could not be determined due to a transient error.
+					case ProductCheckStatus.TransientFailure:
+						Debug.WriteLine(ProductCheckTransientErrorWarning);
+						callDetails.BuildDebugInformationPrefix = sb =>
+						{
+							sb.AppendLine("# Warnings:");
+							sb.AppendLine($"- {ProductCheckTransientErrorWarning}");
+						};
+						break;
+				}
 
 			diagnostic.EndState = response.ApiCall;
 			response.ApiCall.AuditTrail = AuditTrail;
@@ -692,10 +715,14 @@ private bool ApplyProductCheckRules(RootResponse response)
 				return true;
 			}
 
-			// Any response besides a 200, 401 or 403 is considered a failure and the check is considered incomplete remaining in the NotChecked state.
+			// Any response besides a 200, 401 or 403 is considered a failure and the check is considered incomplete and marked as a likely transient failure.
 			// This means that the check will run on subsequent requests until we have a valid response to evaluate.
 			// By returning false, the failure to perform the product check will be included in the audit log.
-			if (!response.Success) return false;
+			if (!response.Success)
+			{
+				_connectionPool.ProductCheckStatus = ProductCheckStatus.TransientFailure;
+				return false;
+			}
 
 			// Start by assuming the product is valid
 			_connectionPool.ProductCheckStatus = ProductCheckStatus.ValidProduct;