Azure · microsoft-github-policy-service · Oct 27, 2023 · Sep 7, 2023 · Sep 7, 2023 · Sep 7, 2023
@@ -28,6 +28,7 @@ internal sealed class ClientRetryPolicy : IDocumentClientRetryPolicy
         private readonly GlobalEndpointManager globalEndpointManager;
         private readonly GlobalPartitionEndpointManager partitionKeyRangeLocationCache;
         private readonly bool enableEndpointDiscovery;
+        private readonly bool isPertitionLevelFailoverEnabled;
         private int failoverRetryCount;
 
         private int sessionTokenRetryCount;
@@ -41,8 +42,9 @@ internal sealed class ClientRetryPolicy : IDocumentClientRetryPolicy
         public ClientRetryPolicy(
             GlobalEndpointManager globalEndpointManager,
             GlobalPartitionEndpointManager partitionKeyRangeLocationCache,
+            RetryOptions retryOptions,
             bool enableEndpointDiscovery,
-            RetryOptions retryOptions)
+            bool isPertitionLevelFailoverEnabled)
         {
             this.throttlingRetry = new ResourceThrottleRetryPolicy(
                 retryOptions.MaxRetryAttemptsOnThrottledRequests,
@@ -55,6 +57,7 @@ public ClientRetryPolicy(
             this.sessionTokenRetryCount = 0;
             this.serviceUnavailableRetryCount = 0;
             this.canUseMultipleWriteLocations = false;
+            this.isPertitionLevelFailoverEnabled = isPertitionLevelFailoverEnabled;
         }
 
         /// <summary> 
@@ -247,8 +250,7 @@ private async Task<ShouldRetryResult> ShouldRetryInternalAsync(
             }
 
             // Received 503 due to client connect timeout or Gateway
-            if (statusCode == HttpStatusCode.ServiceUnavailable
-                && ClientRetryPolicy.IsRetriableServiceUnavailable(subStatusCode))
+            if (statusCode == HttpStatusCode.ServiceUnavailable)
             {
                 DefaultTrace.TraceWarning("ClientRetryPolicy: ServiceUnavailable. Refresh cache and retry. Failed Location: {0}; ResourceAddress: {1}",
                     this.documentServiceRequest?.RequestContext?.LocationEndpointToRoute?.ToString() ?? string.Empty,
@@ -265,12 +267,6 @@ private async Task<ShouldRetryResult> ShouldRetryInternalAsync(
             return null;
         }
 
-        private static bool IsRetriableServiceUnavailable(SubStatusCodes? subStatusCode)
-        {
-            return subStatusCode == SubStatusCodes.Unknown ||
-                (subStatusCode.HasValue && subStatusCode.Value.IsSDKGeneratedSubStatus());
-        }
-
         private async Task<ShouldRetryResult> ShouldRetryOnEndpointFailureAsync(
             bool isReadRequest,
             bool markBothReadAndWriteAsUnavailable,
@@ -390,7 +386,7 @@ private ShouldRetryResult ShouldRetryOnSessionNotAvailable()
 
         /// <summary>
         /// For a ServiceUnavailable (503.0) we could be having a timeout from Direct/TCP locally or a request to Gateway request with a similar response due to an endpoint not yet available.
-        /// We try and retry the request only if there are other regions available.
+        /// We try and retry the request only if there are other regions available. The retry logic is applicable for single master write accounts as well.
         /// </summary>
         private ShouldRetryResult ShouldRetryOnServiceUnavailable()
         {
@@ -401,9 +397,11 @@ private ShouldRetryResult ShouldRetryOnServiceUnavailable()
             }
 
             if (!this.canUseMultipleWriteLocations
-                    && !this.isReadRequest)
+                    && !this.isReadRequest
+                    && !this.isPertitionLevelFailoverEnabled)
             {
-                // Write requests on single master cannot be retried, no other regions available
+                // Write requests on single master cannot be retried if partition level failover is disabled.
+                // This means there are no other regions available to serve the writes.
                 return ShouldRetryResult.NoRetry();
             }
 

@@ -608,7 +608,7 @@ public Func<HttpClient> HttpClientFactory
         /// <summary>
         /// Enable partition key level failover
         /// </summary>
-        internal bool EnablePartitionLevelFailover { get; set; } = false;
+        internal bool EnablePartitionLevelFailover { get; set; } = ConfigurationManager.IsPartitionLevelFailoverEnabled(defaultValue: false);
 
         /// <summary>
         /// Quorum Read allowed with eventual consistency account or consistent prefix account.
@@ -752,6 +752,7 @@ internal virtual ConnectionPolicy GetConnectionPolicy(int clientId)
         {
             this.ValidateDirectTCPSettings();
             this.ValidateLimitToEndpointSettings();
+            this.ValidatePartitionLevelFailoverSettings();
 
             ConnectionPolicy connectionPolicy = new ConnectionPolicy()
             {
@@ -888,6 +889,16 @@ private void ValidateLimitToEndpointSettings()
             }
         }
 
+        private void ValidatePartitionLevelFailoverSettings()
+        {
+            if (this.EnablePartitionLevelFailover
+                && (this.ApplicationPreferredRegions == null || this.ApplicationPreferredRegions.Count == 0)
+                && string.IsNullOrEmpty(this.ApplicationRegion))
+            {
+                throw new ArgumentException($"Either {nameof(this.ApplicationPreferredRegions)} or {nameof(this.ApplicationRegion)} is required when {nameof(this.EnablePartitionLevelFailover)} is enabled.");
+            }
+        }
+
         private void ValidateDirectTCPSettings()
         {
             string settingName = string.Empty;

@@ -13,17 +13,19 @@ internal sealed class RetryPolicy : IRetryPolicyFactory
         private readonly GlobalPartitionEndpointManager partitionKeyRangeLocationCache;
         private readonly GlobalEndpointManager globalEndpointManager;
         private readonly bool enableEndpointDiscovery;
+        private readonly bool isPertitionLevelFailoverEnabled;
         private readonly RetryOptions retryOptions;
 
         /// <summary>
         /// Initialize the instance of the RetryPolicy class
         /// </summary>
         public RetryPolicy(
-            GlobalEndpointManager globalEndpointManager, 
+            GlobalEndpointManager globalEndpointManager,
             ConnectionPolicy connectionPolicy,
             GlobalPartitionEndpointManager partitionKeyRangeLocationCache)
         {
             this.enableEndpointDiscovery = connectionPolicy.EnableEndpointDiscovery;
+            this.isPertitionLevelFailoverEnabled = connectionPolicy.EnablePartitionLevelFailover;
             this.globalEndpointManager = globalEndpointManager;
             this.retryOptions = connectionPolicy.RetryOptions;
             this.partitionKeyRangeLocationCache = partitionKeyRangeLocationCache;
@@ -37,10 +39,11 @@ public IDocumentClientRetryPolicy GetRequestPolicy()
             ClientRetryPolicy clientRetryPolicy = new ClientRetryPolicy(
                 this.globalEndpointManager,
                 this.partitionKeyRangeLocationCache,
+                this.retryOptions,
                 this.enableEndpointDiscovery,
-                this.retryOptions);
+                this.isPertitionLevelFailoverEnabled);
 
             return clientRetryPolicy;
         }
     }
-}
+}
@@ -89,9 +89,11 @@ public GlobalEndpointManager(IDocumentClientInternal owner, ConnectionPolicy con
             }
         }
 
-        public ReadOnlyCollection<Uri> ReadEndpoints => this.locationCache.ReadEndpoints;
+        public ReadOnlyCollection<Uri> ReadEndpoints => this.locationCache.ReadEndpoints;
+
+        public ReadOnlyCollection<Uri> AccountReadEndpoints => this.locationCache.AccountReadEndpoints;
 
-        public ReadOnlyCollection<Uri> WriteEndpoints => this.locationCache.WriteEndpoints;
+        public ReadOnlyCollection<Uri> WriteEndpoints => this.locationCache.WriteEndpoints;
 
         public int PreferredLocationCount => this.connectionPolicy.PreferredLocations != null ? this.connectionPolicy.PreferredLocations.Count : 0;
 

@@ -134,11 +134,20 @@ public override bool TryMarkEndpointUnavailableForPartitionKeyRange(
 
             PartitionKeyRangeFailoverInfo partionFailover = this.PartitionKeyRangeToLocation.Value.GetOrAdd(
                 partitionKeyRange,
-                (_) => new PartitionKeyRangeFailoverInfo(failedLocation));
-
+                (_) => new PartitionKeyRangeFailoverInfo(failedLocation));
+
+            // For any single master write accounts, the next locations to fail over will be the read regions configured at the account level.
+            // For multi master write accounts, since all the regions are treated as write regions, the next locations to fail over
+            // will be the preferred read regions that are configured in the application preferred regions in the CosmosClientOptions.
+            bool isSingleMasterWriteAccount = !this.globalEndpointManager.CanUseMultipleWriteLocations(request);
+
+            ReadOnlyCollection<Uri> nextLocations = isSingleMasterWriteAccount
+                ? this.globalEndpointManager.AccountReadEndpoints
+                : this.globalEndpointManager.ReadEndpoints;
+
             // Will return true if it was able to update to a new region
             if (partionFailover.TryMoveNextLocation(
-                    locations: this.globalEndpointManager.ReadEndpoints,
+                    locations: nextLocations,
                     failedLocation: failedLocation))
             {
                 DefaultTrace.TraceInformation("Partition level override added to new location. PartitionKeyRange: {0}, failedLocation: {1}, new location: {2}",

@@ -13,6 +13,8 @@ internal interface IGlobalEndpointManager : IDisposable
     {
         ReadOnlyCollection<Uri> ReadEndpoints { get; }
 
+        ReadOnlyCollection<Uri> AccountReadEndpoints { get; }
+
         ReadOnlyCollection<Uri> WriteEndpoints { get; }
 
         int PreferredLocationCount { get; }

@@ -101,6 +101,11 @@ public ReadOnlyCollection<Uri> ReadEndpoints
             }
         }
 
+        /// <summary>
+        /// Gets list of account level read endpoints.
+        /// </summary>
+        public ReadOnlyCollection<Uri> AccountReadEndpoints => this.locationInfo.AccountReadEndpoints;
+
         /// <summary>
         /// Gets list of write endpoints ordered by
         /// 1. Preferred location
@@ -491,20 +496,35 @@ private void UpdateLocationCache(
 
                 if (readLocations != null)
                 {
-                    ReadOnlyCollection<string> availableReadLocations;
-                    nextLocationInfo.AvailableReadEndpointByLocation = this.GetEndpointByLocation(readLocations, out availableReadLocations);
+                    nextLocationInfo.AvailableReadEndpointByLocation = this.GetEndpointByLocation(
+                        readLocations,
+                        out ReadOnlyCollection<string> availableReadLocations);
+
                     nextLocationInfo.AvailableReadLocations = availableReadLocations;
+                    nextLocationInfo.AccountReadEndpoints = nextLocationInfo.AvailableReadEndpointByLocation.Select(x => x.Value).ToList().AsReadOnly();
                 }
 
                 if (writeLocations != null)
                 {
-                    ReadOnlyCollection<string> availableWriteLocations;
-                    nextLocationInfo.AvailableWriteEndpointByLocation = this.GetEndpointByLocation(writeLocations, out availableWriteLocations);
+                    nextLocationInfo.AvailableWriteEndpointByLocation = this.GetEndpointByLocation(
+                        writeLocations,
+                        out ReadOnlyCollection<string> availableWriteLocations);
+
                     nextLocationInfo.AvailableWriteLocations = availableWriteLocations;
                 }
 
-                nextLocationInfo.WriteEndpoints = this.GetPreferredAvailableEndpoints(nextLocationInfo.AvailableWriteEndpointByLocation, nextLocationInfo.AvailableWriteLocations, OperationType.Write, this.defaultEndpoint);
-                nextLocationInfo.ReadEndpoints = this.GetPreferredAvailableEndpoints(nextLocationInfo.AvailableReadEndpointByLocation, nextLocationInfo.AvailableReadLocations, OperationType.Read, nextLocationInfo.WriteEndpoints[0]);
+                nextLocationInfo.WriteEndpoints = this.GetPreferredAvailableEndpoints(
+                    endpointsByLocation: nextLocationInfo.AvailableWriteEndpointByLocation,
+                    orderedLocations: nextLocationInfo.AvailableWriteLocations,
+                    expectedAvailableOperation: OperationType.Write,
+                    fallbackEndpoint: this.defaultEndpoint);
+
+                nextLocationInfo.ReadEndpoints = this.GetPreferredAvailableEndpoints(
+                    endpointsByLocation: nextLocationInfo.AvailableReadEndpointByLocation,
+                    orderedLocations: nextLocationInfo.AvailableReadLocations,
+                    expectedAvailableOperation: OperationType.Read,
+                    fallbackEndpoint: nextLocationInfo.WriteEndpoints[0]);
+
                 this.lastCacheUpdateTimestamp = DateTime.UtcNow;
 
                 DefaultTrace.TraceInformation("Current WriteEndpoints = ({0}) ReadEndpoints = ({1})",
@@ -534,8 +554,7 @@ private ReadOnlyCollection<Uri> GetPreferredAvailableEndpoints(ReadOnlyDictionar
 
                     foreach (string location in currentLocationInfo.PreferredLocations)
                     {
-                        Uri endpoint;
-                        if (endpointsByLocation.TryGetValue(location, out endpoint))
+                        if (endpointsByLocation.TryGetValue(location, out Uri endpoint))
                         {
                             if (this.IsEndpointUnavailable(endpoint, expectedAvailableOperation))
                             {
@@ -560,9 +579,8 @@ private ReadOnlyCollection<Uri> GetPreferredAvailableEndpoints(ReadOnlyDictionar
                 {
                     foreach (string location in orderedLocations)
                     {
-                        Uri endpoint;
                         if (!string.IsNullOrEmpty(location) && // location is empty during manual failover
-                            endpointsByLocation.TryGetValue(location, out endpoint))
+                            endpointsByLocation.TryGetValue(location, out Uri endpoint))
                         {
                             endpoints.Add(endpoint);
                         }
@@ -634,6 +652,7 @@ public DatabaseAccountLocationsInfo(ReadOnlyCollection<string> preferredLocation
                 this.AvailableWriteEndpointByLocation = new ReadOnlyDictionary<string, Uri>(new Dictionary<string, Uri>(StringComparer.OrdinalIgnoreCase));
                 this.AvailableReadEndpointByLocation = new ReadOnlyDictionary<string, Uri>(new Dictionary<string, Uri>(StringComparer.OrdinalIgnoreCase));
                 this.WriteEndpoints = new List<Uri>() { defaultEndpoint }.AsReadOnly();
+                this.AccountReadEndpoints = new List<Uri>() { defaultEndpoint }.AsReadOnly();
                 this.ReadEndpoints = new List<Uri>() { defaultEndpoint }.AsReadOnly();
             }
 
@@ -645,6 +664,7 @@ public DatabaseAccountLocationsInfo(DatabaseAccountLocationsInfo other)
                 this.AvailableWriteEndpointByLocation = other.AvailableWriteEndpointByLocation;
                 this.AvailableReadEndpointByLocation = other.AvailableReadEndpointByLocation;
                 this.WriteEndpoints = other.WriteEndpoints;
+                this.AccountReadEndpoints = other.AccountReadEndpoints;
                 this.ReadEndpoints = other.ReadEndpoints;
             }
 
@@ -655,6 +675,7 @@ public DatabaseAccountLocationsInfo(DatabaseAccountLocationsInfo other)
             public ReadOnlyDictionary<string, Uri> AvailableReadEndpointByLocation { get; set; }
             public ReadOnlyCollection<Uri> WriteEndpoints { get; set; }
             public ReadOnlyCollection<Uri> ReadEndpoints { get; set; }
+            public ReadOnlyCollection<Uri> AccountReadEndpoints { get; set; }
         }
 
         [Flags]

@@ -9,12 +9,19 @@ namespace Microsoft.Azure.Cosmos
     internal static class ConfigurationManager
     {
         /// <summary>
-        /// A read-only string containing the environment variablename for enabling replica validation.
-        /// This will eventually be removed oncereplica valdiatin is enabled by default for both preview
+        /// A read-only string containing the environment variable name for enabling replica validation.
+        /// This will eventually be removed once replica valdiatin is enabled by default for both preview
         /// and GA.
         /// </summary>
         internal static readonly string ReplicaConnectivityValidationEnabled = "AZURE_COSMOS_REPLICA_VALIDATION_ENABLED";
 
+        /// <summary>
+        /// A read-only string containing the environment variable name for enabling per partition automatic failover.
+        /// This will eventually be removed once per partition automatic failover is enabled by default for both preview
+        /// and GA.
+        /// </summary>
+        internal static readonly string PartitionLevelFailoverEnabled = "AZURE_COSMOS_PARTITION_LEVEL_FAILOVER_ENABLED";
+
         public static T GetEnvironmentVariable<T>(string variable, T defaultValue)
         {
             string value = Environment.GetEnvironmentVariable(variable);
@@ -50,5 +57,22 @@ public static bool IsReplicaAddressValidationEnabled(
                         variable: ConfigurationManager.ReplicaConnectivityValidationEnabled,
                         defaultValue: replicaValidationDefaultValue);
         }
+
+        /// <summary>
+        /// Gets the boolean value of the partition level failover environment variable. Note that, partition level failover
+        /// is disabled by default for both preview and GA releases. The user can set the  respective environment variable
+        /// 'AZURE_COSMOS_PARTITION_LEVEL_FAILOVER_ENABLED' to override the value for both preview and GA. The method will
+        /// eventually be removed, once partition level failover is enabled by default for  both preview and GA.
+        /// </summary>
+        /// <param name="defaultValue">A boolean field containing the default value for partition level failover.</param>
+        /// <returns>A boolean flag indicating if partition level failover is enabled.</returns>
+        public static bool IsPartitionLevelFailoverEnabled(
+            bool defaultValue)
+        {
+            return ConfigurationManager
+                    .GetEnvironmentVariable(
+                        variable: ConfigurationManager.PartitionLevelFailoverEnabled,
+                        defaultValue: defaultValue);
+        }
     }
 }