Hybrid Connection Manager from Linux App Service

Question

Hybrid Connection Manager from Linux App Service

Mike 6

I have a .NET 5.0 application that can connect and query from a Windows App Service just fine but when deployed to a Linux App Service the query times out. The application runs fine, my authentication code to Azure AD functions, top menu renders etc but when the application attempts to create the DB connection, it times out.

The HCM shows connected on both the App Service and on-prem sides.

Is there anything different that needs to be done either in the Azure setup or .NET 5.0 code for a HCM on a Linux Azure App Service?

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Answer 1

Grmacjon-MSFT 19,151 Moderator

Hi @Mike ,

Thanks for bringing this to our attention. That's odd behavior. Can you please share the exact error message you are getting? Does your host have outbound access to Azure on port 443?

Based on this doc, if your status says Connected but your app cannot reach your endpoint then:

Make sure you're using a DNS name in your Hybrid Connection. If you use an IP address then the required client DNS lookup may not happen. If the client running in your web app doesn't do a DNS lookup, then the Hybrid Connection will not work
Check that the DNS name used in your Hybrid Connection can resolve from the HCM host. Check the resolution using nslookup EndpointDNSname where EndpointDNSname is an exact match to what is used in your Hybrid Connection definition.
Test access from your HCM host to your endpoint using the PowerShell command Test-NetConnection EndpointDNSname -P Port If you cannot reach the endpoint from your HCM host then check firewalls between the two hosts including any host-based firewalls on the destination host.

Hope that helps. Please let us know if you have further questions

Thanks,
Grace

--If the reply is helpful, please Upvote and Accept as answer--

Mike 6 Reputation points

2021-10-14T22:32:45.563+00:00

Note that the same CODE works from a WINDOWS App Service using the same HCM connection (relay, host), same connection string, etc.

So the only change being the App Plan (Linux) and App Service (Linux)

I replaced the SQL Server and DB names in the error and snipped some of the call stack to make it under the maximum characters size for this post.

Microsoft.EntityFrameworkCore.Database.Connection[20004]
An error occurred using the connection to database '<the database name>' on server '<the server name>'.
Microsoft.EntityFrameworkCore.Query[10100]
An exception occurred while iterating over the results of a query for context type 'AppMan.Data.<the database name>'.
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.Net.Internals.SocketExceptionFactory+ExtendedSocketException (00000005, 0xFFFDFFFF): Name or service not known
Mike 6 Reputation points

2021-10-20T15:52:53.443+00:00

nslookup in a SSH session on the App Service (remember this is Linux) does return an IP address but I don't know how to tell if it's correct or not. If I do a nslookup of a made up endpoint it returns a "can't find server" so it must be resolving my real EndpointDNSname.

Test-NetConnection results in a

-bash: Test-NetConnection: command not found
Mike 6 Reputation points

2021-10-20T16:58:42.227+00:00

Ironically on the Windows App Service where the HCM does work if I start a console session on the Windows App Service:

C:\home\site\wwwroot>nslookup REPLCAPA
*** UnKnown can't find REPLCAPA Non-existent domain

C:\home\site\wwwroot>Test-NetConnection REPLCAPA -P 1433
'Test-NetConnection' is not recognized as an internal or external command, operable program or batch file.
Mike 6 Reputation points

2021-10-20T18:36:03.397+00:00

Update I can ping the on-prem server from the Linux App Service
Grmacjon-MSFT 19,151 Reputation points Moderator

2021-10-23T00:01:58.847+00:00

Hi @Mike ,

Apologizes for the delayed response. Thanks for the update. What changes did you make that enabled you to ping the on-prem server from your Linux App Service? did you enable the TCP/Named Pipes Protocol on the SQL Server instance from the SQL Server Configuration Manager console?
Kenny Lozowski (CMH) 1 Reputation point

2021-10-26T17:48:33.273+00:00

I am experiencing the same problem. An Windows Azure Function running in .NET 5.0 isolated mode is able to connect using a Hybrid Connection when using a Windows App Service plan, but throws an exception and fails when published as a Linux Azure Function using a Linux App Service plan.

On the HCM host I have tried using a hostname with an implicit suffix and a fully qualified host name, and both nslookup EndpointDNSname and Test-NetConnection EndpointDNSname -P Port works fine, so DNS resolution isn't the issue. The HCM is running on a Windows VM in the on-premise environment
Mike 6 Reputation points

2021-10-27T17:37:59.117+00:00

There were no changes, my confusion was thinking you wanted me to run the nslookup and "Test-NetConnection EndpointDNSname -P Port" commands on the App Service. I didn't realize you were just leveraging the troubleshooting steps in docs on HCM.

The HCM host is fine, it works for the Windows App Service so of course the nslookup and "Test-NetConnection EndpointDNSname -P Port" commands work there just fine.

nslookup returns the route and IP of the DC then the SQL Server.

Test-NetConnection

ComputerName : servername
RemoteAddress : IP Address of the server
RemotePort : 1433
InterfaceAlias : Ethernet0
SourceAddress : IP Address of the host
TcpTestSucceeded : True
Ryan Hill 30,281 Reputation points Microsoft Employee Moderator

2021-10-29T02:47:22.05+00:00

@Kenny Lozowski (CMH) can you send us email to AzCommunity[at]microsoft[dot]com ATTN: Ryan so we can work more closely with you regarding this matter?

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Hybrid Connection Manager from Linux App Service

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