Dockerize a dotnet core application with SQL connectivity

Before reading this article, I am assuming that you know Docker, Dotnet core and have a dotnet core application which is trying to connect to SQL server. Read how to build aspnet core app, docker and run the docker container.

If docker container is running and you are not able to connect to database, this blog should help you fix it. 

Prerequisite - 

• Make sure code is working via running aspnet core locally via visual studio or command line.
• Port 1433 is opened for connecting to SQL server.

Solution

If you have Docker file ready, it should somewhat look like below file - 

FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build-env

WORKDIR /app

# Copy csproj and restore as distinct layers

COPY /SampleAPI/*.csproj ./

RUN dotnet restore

# Copy everything else and build

COPY . .

WORKDIR /app/SampleAPI

RUN dotnet publish -c Production -o publish

# Build runtime image

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1

WORKDIR /app/SampleAPI

COPY --from=build-env /app/SampleAPI .

WORKDIR /app/SampleAPI/bin/Production/netcoreapp3.1

ENTRYPOINT ["dotnet", "SampleAPI.dll"]

Add following lines to make database connectivity  

#To connect to database

RUN sed -i 's/MinProtocol = TLSv1.2/MinProtocol = TLSv1/g' /etc/ssl/openssl.cnf

RUN sed -i 's/MinProtocol = TLSv1.2/MinProtocol = TLSv1/g' /usr/lib/ssl/openssl.cnf

RUN sed -i 's/DEFAULT@SECLEVEL=2/DEFAULT@SECLEVEL=1/g' /etc/ssl/openssl.cnf

RUN sed -i 's/DEFAULT@SECLEVEL=2/DEFAULT@SECLEVEL=1/g' /usr/lib/ssl/openssl.cnf

The above lines invoke 'sed'(stream Editor) to open file and edit it. 

• Line 1 is modfying '/etc/ssl/openssl.conf' file and replacing MinProtocal = TLSv1.2 to MinProtocol = TLSv1. 
• Line 2 is modifying same protocol in another file. 
• Line 3 is setting the security level from DEFAULT@SECLEVEL=2 to DEFAULT@SECLEVEL=1. 
• Line 4 is modifying the same in another file.

Note: You can add first 2 OR last 2 OR all lines depending upon connection issue with database.

Final Docker file will look something like that - 

FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build-env

WORKDIR /app

# Copy csproj and restore as distinct layers

COPY /SampleAPI/*.csproj ./

RUN dotnet restore

# Copy everything else and build

COPY . .

WORKDIR /app/SampleAPI

RUN dotnet publish -c Production -o publish

# Build runtime image

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1

#To connect to database

RUN sed -i 's/MinProtocol = TLSv1.2/MinProtocol = TLSv1/g' /etc/ssl/openssl.cnf

RUN sed -i 's/MinProtocol = TLSv1.2/MinProtocol = TLSv1/g' /usr/lib/ssl/openssl.cnf

RUN sed -i 's/DEFAULT@SECLEVEL=2/DEFAULT@SECLEVEL=1/g' /etc/ssl/openssl.cnf

RUN sed -i 's/DEFAULT@SECLEVEL=2/DEFAULT@SECLEVEL=1/g' /usr/lib/ssl/openssl.cnf

WORKDIR /app/SampleAPI

COPY --from=build-env /app/SampleAPI .

WORKDIR /app/SampleAPI/bin/Production/netcoreapp3.1

ENTRYPOINT ["dotnet", "SampleAPI.dll"]

Build Docker image

docker build -t sampleapi:latest .

Run Docker container 

docker run -rm -p 5000:80 sampleapi:latest

where 80 is default port of docker container and 5000 port to expose to internet. 

Browse the API and it should respond with successful database connection. 

Alternatively

bionic version of aspnet core image can be used - 

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-bionic AS build-env

WORKDIR /app

# Copy csproj and restore as distinct layers

COPY /DPRR-API/*.csproj ./

RUN dotnet restore

# Copy everything else and build

COPY . .

WORKDIR /app/DPRR-API

RUN dotnet publish -c Production -o publish

# Build runtime image

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

WORKDIR /app/DPRR-API

COPY --from=build-env /app/DPRR-API .

WORKDIR /app/DPRR-API/bin/Production/netcoreapp3.1

ENTRYPOINT ["dotnet", "DPRR-API.dll"]

By using bionic image of aspnet core(mcr.microsoft.com/dotnet/core/sdk:3.1-bionic), there should not be any need of modifying the TLS or default settings.

Please share your feedback if it works for you.