Docker container can't connect to SQL Server on a remote server

Question

I have a container hosted ASP.NET Core application but it can't connect to SQL Server on a remote server.

The error 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. Verify that the instance name is correct and that SQL Server is configured to allow remote connections.

This is what I already checked:

• Try to disable firewall on host machine and DB server. : still get the error
• Edit connection string to use IP and port : still get the error
• Ping from application container to DB server: I can ping to DB server normally
• Connect to database server via SQL Server Management Studio: I can connect normally

So I think that the container can see the DB server but can't connect. What's the other thing should I check?

Thank you very much for your help.

Update

Dockerfile:

FROM mcr.microsoft.com/dotnet/core/aspnet:3.0 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 1433

#our sql server was use this port for connect
EXPOSE 64608

FROM mcr.microsoft.com/dotnet/core/sdk:3.0 AS build
WORKDIR /src

COPY Web.API.sln ./
COPY MyProject.Core/*.csproj ./MyProject.Core/
COPY MyProject.API/*.csproj ./MyProject.API/

RUN dotnet restore
COPY . .

WORKDIR /src/MyProject.API
RUN dotnet build -c Release -o /app

FROM build AS publish
RUN dotnet publish -c Release -o /app

FROM base AS final
WORKDIR /app
COPY --from=publish /app .
ENTRYPOINT ["dotnet", "MyProject.API.dll"]

Run Docker Command:

docker build -t myproject-api:latest .

docker run -d -p 7991:80 --name myproject-api myproject-api:latest

Connection String:

"data source=172.16.0.88\\SQL_DEV,64608; initial catalog=MyProject; persist security info=True; user id=myuser; password=mypassword;"

Answer 1

This is most probably because of the connection string.

Change your connection string to something like below

Server=172.16.0.88\\SQL_DEV,64608;Database=MyProject;UserId=myuser;Password=mypassword

or

Server=172.16.0.88,64608;Database=MyProject;User Id=myuser;Password=mypassword

Which ever works.

Answer 2

I had a same problem and I changed my Dockerfile image

I replace It

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim AS base

with this line

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-bionic AS base

Now It works !