ASP.NET Core Dev Notes: Using Alpine Image and Adding Health Checks

Introduction

Using Docker to deploy AspNetCore applications has become standard practice. I previously always used images like mcr.microsoft.com/dotnet/aspnet:8.0, which is straightforward, but Alpine-based images can further optimize image size.

Many open-source tools' Docker images include health checks, and I took the opportunity to add them this time as well.

PS: The example project in this article comes from a project that was nearly canceled, "IdentityServerLite". I'll write an article to introduce it later~

Adding Health Checks (健康检查)

Register the service

builder.Services.AddHealthChecks();

Configure the middleware

app.MapHealthChecks("/healthz");

After that, test it. After running locally, you can see the word "Healthy" by visiting http://host:port/healthz.

Modify docker-compose

Add a healthcheck configuration below the application settings.

The image mcr.microsoft.com/dotnet/aspnet comes with wget built-in, so you can use it directly to request the health check endpoint. If you were using curl, you would have to install it.

version: '3.6'

services:
  web:
    image: ${DOCKER_REGISTRY-}web
    container_name: ids-lite
    restart: always
    environment:
      - ASPNETCORE_ENVIRONMENT=Production
      - ASPNETCORE_URLS=http://+:80
    build:
      context: .
    volumes:
      - .:/app
    networks:
      - swag
    healthcheck:
      test: ["CMD-SHELL", "wget --spider http://localhost:80/healthz || exit"]
      interval: 10s
      timeout: 5s
      retries: 5

networks:
  swag:
    name: swag
    external: true

Switching to Alpine Base Image

Before configuring CICD, I used the FrameworkDependent approach to deploy with Docker. For details, see my previous article: Asp-Net-Core开发笔记：FrameworkDependent搭配docker部署

Switching to Alpine can reduce the image size by half, from about 240MB down to around 100MB.

Modify the Dockerfile

Just add -alpine after 8.0

FROM mcr.microsoft.com/dotnet/aspnet:8.0-alpine AS base
RUN apk add --no-cache icu-libs
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM base AS final
WORKDIR /app
COPY . .
ENTRYPOINT ["./IdsLite.Api"]

ENV TZ=Asia/Shanghai
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone

Re-publishing

Previously, when publishing locally, the runtime selected was linux-x64.

The executable published this way depends on glibc.

However, the Alpine base image uses musl libc.

So, it is necessary to select the linux-musl-x64 runtime, then republish.

dotnet publish -r linux-musl-x64

Done!

Reference Materials

• https://www.cnblogs.com/podolski/p/16603177.html