Docker

🟢 1️⃣ What is Docker?

• Docker is a tool to package applications with all dependencies into a container.

• Container = isolated environment that runs your app anywhere (Windows, Linux, cloud).

• Benefit: “It works on my machine” problem is solved.

Analogy: Docker is like a shipping container for your app. It includes your app, .NET runtime, libraries, and everything needed.

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🟢 2️⃣ Why Use Docker with .NET Core?

1. Cross-platform: Run .NET Core apps on Linux, Windows, or cloud.

2. Easy deployment: Package app + dependencies.

3. Isolation: No conflicts between apps.

4. Microservices: Each service can run in its own container.

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🟢 3️⃣ Steps to Dockerize a .NET Core App

Step 1: Create a .NET Core App

dotnet new webapi -n MyWebApi
cd MyWebApi
dotnet build
dotnet run

• Your API runs locally on http://localhost:5000.

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Step 2: Create a Dockerfile

• In the root folder, create a file named Dockerfile (no extension):

# 1. Base image with .NET runtime
FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80

# 2. Build image with SDK
FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["MyWebApi.csproj", "./"]
RUN dotnet restore "./MyWebApi.csproj"
COPY . .
RUN dotnet publish "MyWebApi.csproj" -c Release -o /app/publish

# 3. Final image
FROM base AS final
WORKDIR /app
COPY --from=build /app/publish .
ENTRYPOINT ["dotnet", "MyWebApi.dll"]

Explanation:

• Stage 1 (base): Runtime image to run the app.

• Stage 2 (build): SDK image to build and publish the app.

• Stage 3 (final): Copy published files to runtime image and run.

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Step 3: Build Docker Image

docker build -t mywebapi:1.0 .

• mywebapi → image name, 1.0 → version tag.

• Docker reads the Dockerfile and creates the image.

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Step 4: Run the Container

docker run -d -p 8080:80 --name mywebapi_container mywebapi:1.0

• -d → run in background

• -p 8080:80 → map container port 80 to local port 8080

• --name → container name

Now open http://localhost:8080 → your API is running inside a Docker container!

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Step 5: (Optional) Docker Compose

• Useful if you have multiple services (like API + database).

• Create docker-compose.yml:

version: '3.8'
services:
  webapi:
    image: mywebapi:1.0
    ports:
      - "8080:80"
  db:
    image: mcr.microsoft.com/mssql/server:2019-latest
    environment:
      SA_PASSWORD: "Your_password123"
      ACCEPT_EULA: "Y"
    ports:
      - "1433:1433"

• Run with: docker-compose up -d

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🟢 4️⃣ Tips

1. Always use multi-stage Dockerfile → keeps image size small.

2. Expose only needed ports (EXPOSE 80).

3. Use environment variables for secrets/configuration.

4. Use .dockerignore to exclude unnecessary files (like bin, obj).

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🟢 5️⃣ Summary

• Docker packages your .NET Core app + dependencies into a container.

• Steps:

  1. Create .NET Core app

  2. Write Dockerfile

  3. Build Docker image (docker build)

  4. Run container (docker run)

• Optional: Use Docker Compose for multi-container apps.