Bits of .NET

📦 Dockerizing Existing Applications

Containerizing legacy apps is challenging. Step-by-step guide to containerize existing .NET applications.

📝 Step 1-4: Dockerfile Creation

# Step 1: Analyze Application
- Identify dependencies
- Check .NET Framework version
- List external dependencies
- Check configuration files

# Step 2: Create Dockerfile
FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
COPY . .
ENTRYPOINT ["dotnet", "MyApp.dll"]

# Step 3: Multi-Stage Build
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY *.sln .
COPY *.csproj .
RUN dotnet restore

COPY . .
RUN dotnet publish -c Release -o /app

FROM mcr.microsoft.com/dotnet/aspnet:6.0
WORKDIR /app
COPY --from=build /app .
ENTRYPOINT ["dotnet", "MyApp.dll"]

# Step 4: Environment Variables
ENV ASPNETCORE_ENVIRONMENT=Production
ENV ConnectionStrings__Default=Server=db;Database=MyApp;User=sa;Password=...

# Step 5: .dockerignore
bin/
obj/
*.user
*.suo
.git/
*.log

📝 Step 5-8: Build and Deploy

# Step 5: Build Image
docker build -t myapp:latest .

# Step 6: Test Locally
docker run -d -p 8080:80 --name myapp myapp:latest
docker logs -f myapp

# Step 7: Docker Compose (with Database)
version: '3.8'
services:
    app:
        build: .
        ports:
            - "8080:80"
        environment:
            - ConnectionStrings__Default=Server=db;Database=MyApp;User=sa;Password=...
        depends_on:
            - db
    
    db:
        image: mcr.microsoft.com/mssql/server:2022-latest
        environment:
            - ACCEPT_EULA=Y
            - SA_PASSWORD=Your_password123
        volumes:
            - sql-data:/var/opt/mssql

volumes:
    sql-data:

# Step 8: Deploy to Production
docker tag myapp:latest myregistry.azurecr.io/myapp:latest
docker push myregistry.azurecr.io/myapp:latest

✅ Dockerization Benefits

• ✓ Consistent environments
• ✓ Easy deployment
• ✓ Scalability
• ✓ Isolation
• ✓ CI/CD integration