Unable to connect to host's sql server from docker container

Question

I have packaged a ASP.NET MVC 4.7.2 app to a container image. I would like to test it locally by connecting the app in the container to the host's SQL Server.

As suggested from the docker docs, I have substituted all occurrences of localhost in my Web.config with host.docker.internal:

<connectionStrings>
    <add name="WebsiteUsers" connectionString="Data Source=host.docker.internal;Initial Catalog=WebsiteUsers;User Id=admin; password=password" providerName="System.Data.SqlClient" />
...

However, when I run the container with the below command :

docker run --rm -p 8081:80 -d site:latest

There is this IIS server error being thrown:

Server Error in '/' Application.
The network path was not found
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ComponentModel.Win32Exception: The network path was not found

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[Win32Exception (0x80004005): The network path was not found]

[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: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)]
   System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling, SqlAuthenticationProviderManager sqlAuthProviderManager) +1431
   System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions) +1085
   System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions) +70
   System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) +964
   System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) +109

This is how I package the image:

FROM mcr.microsoft.com/dotnet/framework/aspnet:4.7.2-windowsservercore-ltsc2016

SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'Continue'; $verbosePreference='Continue';"]

# The final instruction copies the site you published earlier into the container.
COPY ./bin/Release/PublishOutput/ /inetpub/wwwroot

docker version:

Client:
 Cloud integration: v1.0.20
 Version:           20.10.10
 API version:       1.41
 Go version:        go1.16.9
 Git commit:        b485636
 Built:             Mon Oct 25 07:47:53 2021
 OS/Arch:           windows/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.10
  API version:      1.41 (minimum version 1.24)
  Go version:       go1.16.9
  Git commit:       e2f740d
  Built:            Mon Oct 25 07:43:13 2021
  OS/Arch:          windows/amd64
  Experimental:     false

Answer 1

You need to configure your Sqlserver to support tcp and allow remote access.