Azure Container Apps
An Azure service that provides a general-purpose, serverless container platform.
Intermittent Azure SQL connectivity drop
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Laeya
0
Reputation points
We have an API hosted in Azure Container Apps that connects to an Azure SQL Database using AAD authentication and TLS 1.2. The API runs on a scheduled job that connects and queries the database every 10 minutes, Monday–Friday.
This setup has been working normally, but over the past couple of weeks we’ve been seeing intermittent connection failures. The error returned is:
“A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. (provider: TCP Provider, error: 35 – An internal exception was caught)”
This is thrown as Microsoft.Data.SqlClient.SqlException (0x80131904) .
We checked SQL monitoring in the Azure Portal and do not see any anomalies, spikes in traffic, or indications of issues during the times these failures occur.
Could you please advise on potential causes or steps to diagnose and resolve these intermittent connectivity errors between Azure Container Apps and Azure SQL Database?
Thank you.
Azure Container Apps
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Saraswathi Devadula 13,410 Reputation points Microsoft External Staff Moderator2025-12-03T10:29:30.5766667+00:00 Hello **Laeya
**Could you please confirm if you are able to connect to the SQL database from query editor or SSMS?
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Laeya 0 Reputation points
2025-12-03T10:42:55.78+00:00 Yes, I am
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Praveen Kumar Gudipudi 1,495 Reputation points Microsoft External Staff Moderator2025-12-03T12:10:31.6033333+00:00 Hello Laeya,
Please share me the application logs to troubleshoot your issue.
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Laeya 0 Reputation points
2025-12-03T12:19:39.41+00:00 Microsoft.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 35 - An internal exception was caught)
---> System.ComponentModel.Win32Exception (258): The connection attempt timed out.
at Microsoft.Data.SqlClient.ManagedSni.SniTcpHandle.Connect(String serverName, Int32 port, TimeoutTimer timeout, SqlConnectionIPAddressPreference ipPreference, String cachedFQDN, SQLDNSInfo& pendingDNSInfo)
at Microsoft.Data.SqlClient.ManagedSni.SniTcpHandle..ctor(String serverName, Int32 port, TimeoutTimer timeout, Boolean parallel, SqlConnectionIPAddressPreference ipPreference, String cachedFQDN, SQLDNSInfo& pendingDNSInfo, Boolean tlsFirst, String hostNameInCertificate, String serverCertificateFilename)
at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, SqlCommand command, Boolean callerHasConnectionLock, Boolean asyncClose)
at Microsoft.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, TimeoutTimer timeout, SqlConnectionString connectionOptions, Boolean withFailover)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo serverInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString connectionOptions, SqlCredential credential, TimeoutTimer timeout)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(TimeoutTimer timeout, SqlConnectionString connectionOptions, SqlCredential credential, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance)
at Microsoft.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, Boolean applyTransientFaultHandling, String accessToken, IDbConnectionPool pool, Func`3 accessTokenCallback)
at Microsoft.Data.SqlClient.ConnectionPool.WaitHandleDbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
at Microsoft.Data.SqlClient.ConnectionPool.WaitHandleDbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
at Microsoft.Data.SqlClient.ConnectionPool.WaitHandleDbConnectionPool.WaitForPendingOpen()
--- End of stack trace from previous location ---
at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenInternalAsync(Boolean errorsExpected, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenInternalAsync(Boolean errorsExpected, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenAsync(CancellationToken cancellationToken, Boolean errorsExpected)
at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.InitializeReaderAsync(AsyncEnumerator enumerator, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.ExecuteAsyncTState,TResult
at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()
at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.SingleOrDefaultAsyncTSource
at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.SingleOrDefaultAsyncTSource
at MyClass.MyMethodAsync(CancellationToken cancellationToken) in xxxx.cs:line ???
at MyClass.MyMethodAsync(CancellationToken cancellationToken) in xxxx.cs:line ???
at MyClass.MyMethodAsync(CancellationToken cancellationToken) in xxxx.cs:line ???
ClientConnectionId:00000000-0000-0000-0000-000000000000
Error Number:258,State:0,Class:20
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Praveen Kumar Gudipudi 1,495 Reputation points Microsoft External Staff Moderator
2025-12-03T12:59:10.64+00:00 Hello Laeya,
I hope your container app is in a consumption plan, right?
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Laeya 0 Reputation points
2025-12-03T14:42:10.6066667+00:00 yes, we do
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Praveen Kumar Gudipudi 1,495 Reputation points Microsoft External Staff Moderator
2025-12-04T06:18:02.42+00:00 Hello Laeya,
Because your Container App is running on the Consumption plan, each scheduled execution may trigger a cold start or place the workload on a different node with limited outbound SNAT ports. This can cause intermittent outbound TCP connection failures when connecting to Azure SQL, even if SQL is healthy.
Enabling retry logic, increasing minReplicas, or moving to a dedicated workload profile (or using a NAT Gateway) typically resolves these issues.
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Praveen Kumar Gudipudi 1,495 Reputation points Microsoft External Staff Moderator
2025-12-08T03:57:38.9433333+00:00 Hello Laeya,
We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
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Laeya 0 Reputation points
2025-12-09T15:53:32.65+00:00 Hi Praveen,
Sorry for not getting back to you sooner but we were trying a few things which unfortunately did not solve the problem.
Changes we made since yesterday morning:
- Use of NAT Gateway
- Increased container resource allocation
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