🚀 Dockerizing and Setting Up CI/CD for a .NET API with GitLab

In this guide, we'll walk through the steps to containerize a .NET API using Docker and set up a CI/CD pipeline with GitLab. This setup enables automatic building, testing, and deployment of your application, ensuring a smoother development lifecycle.

✅ Prerequisites
Before getting started, make sure you have the following:

• A .NET API project (.NET 8 or compatible)
• A GitLab account with a repository
• Docker installed on your local machine

🐳 Dockerizing the .NET API

• Create a Dockerfile in the root of your project directory. This file defines how to build your Docker image.

# Base image for running the app
FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

# Build image
FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
WORKDIR /src
COPY ["blog.backend.api/blog.backend.api.csproj", "blog.backend.api/"]
RUN dotnet restore "blog.backend.api/blog.backend.api.csproj"
COPY . .
WORKDIR "/src/blog.backend.api"
RUN dotnet build "blog.backend.api.csproj" -c Release -o /app/build

# Publish image
FROM build AS publish
RUN dotnet publish "blog.backend.api.csproj" -c Release -o /app/publish /p:UseAppHost=false

# Final image
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "blog.backend.api.dll"]

⚙️ Setting Up the GitLab CI/CD Pipeline

• Create a .gitlab-ci.yml file at the root of your repository:

image: docker:latest

services:
  - docker:dind

stages:
  - build
  - test
  - deploy

variables:
  DOCKER_IMAGE: registry.gitlab.com/yash-project/blogApplicationAPI
  DOCKER_TAG: latest

build:
  stage: build
  script:
    - docker build -f Dockerfile -t $DOCKER_IMAGE:$DOCKER_TAG .
    - echo "$CI_REGISTRY_PASSWORD" | docker login -u "$CI_REGISTRY_USER" --password-stdin $CI_REGISTRY
    - docker push $DOCKER_IMAGE:$DOCKER_TAG

test:
  stage: test
  image: mcr.microsoft.com/dotnet/sdk:8.0
  script:
    - dotnet test

deploy:
  stage: deploy
  script:
    - echo "Deploying using Docker Compose..."
    - docker-compose up -d
  only:
    - main

This pipeline includes three stages:

• Build: Builds and pushes the Docker image to GitLab's container registry.
• Test: Runs your unit/integration tests.
• Deploy: Spins up the container using Docker Compose.

📦 Docker Compose Deployment
Create a docker-compose.yml file:

version: "3.9"

services:
  blog-backend-api:
    image: registry.gitlab.com/yash-project/blogApplicationAPI:latest
    ports:
      - "80:80"

• This simple setup pulls the latest image and runs your API on port 80.

🎯 Conclusion
By combining Docker with GitLab CI/CD, you now have a robust and automated workflow for building, testing, and deploying your .NET API. This approach streamlines development and ensures consistency across environments.