.Net

🟢 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.

🟢 2️⃣ Why Use Docker with .NET Core?

Cross-platform: Run .NET Core apps on Linux, Windows, or cloud.
Easy deployment: Package app + dependencies.
Isolation: No conflicts between apps.
Microservices: Each service can run in its own container.

🟢 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.

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.

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.

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!

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

🟢 4️⃣ Tips

Always use multi-stage Dockerfile → keeps image size small.
Expose only needed ports (EXPOSE 80).
Use environment variables for secrets/configuration.
Use .dockerignore to exclude unnecessary files (like bin, obj).

🟢 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.

Monday, 22 September 2025

Docker