Docker on Windows Connecting to sql server from dotnetcore app

Question

I've built a simple api using asp.net core that returns some data from a sql server database.

It runs fine in VS and from the command line, but when i build and run the app as a docker container on my windows 10 machine when i call the api i keep getting this error

System.Data.SqlClient.SqlException: Connection Timeout Expired. The timeout period elapsed during the post-login phase. The connection could have timed out while waiting for server to complete the login process and respond; Or it could have timed out while attempting to create multiple active connections. The duration spent while attempting to connect to this server was - [Pre-Login] initialization=425; handshake=265; [Login] initialization=5; authentication=9; [Post-Login] complete=14034; ---> System.ComponentModel.Win32Exception: Unknown error 258

I'm not really sure what this is telling me, it's as if it cant find the sql server machine. Do i have to expose port 1433 somehow in the docker config or when i run the container up?

Answer 1

Not sure if my case was the same as your case, but in my case I was connecting from a docker container to a sql server 2008 R2 running on the host (real pc). I had to install SP3 for sql server 2008 R2 to fix it.

More info here

Answer 2

As Tseng explained in his comment, your containers are in their own network, not in your host's network. You'll want indeed to expose that port (or map to another available port on your host), which you can easily do with Docker Compose. In the example below (that you'd but in a docker-compose.yml file), sql is the name of your database container, 1337 is the local port, and 1433 is the container's port.

sql:
 ports:
 - "1337:1433"