A simple web API in various languages and deployable to Kubernetes (C#)

Introduction

I’m always interested in how different programming languages and their libs/frameworks tackle the same problem. Recently the topic of writing web API’s in whatever language we wanted came up and so I thought, well let’s try to do just that.

The service is maybe too simple for a really good explanation of the frameworks and language features of the languages I’m going to use, but at the same time, I wanted to just do the bare minimum to have something working but enough.

The service is a “echo” service, it will have an endpoint that simply passes back what’s sent to it (prefixed with some text) and also supply livez and readyz as I want to also create a Dockerfile and the associated k8s yaml files to deploy the service.

The healthz endpoint is deprecated as of k8s v1.16, so we’ll leave that one out.

It should be noted that there are (in some cases) other frameworks that can be used and optimisations, my interest is solely to get some basic Web API deployed to k8s that works, so you may have preferences for other ways to do this.

C# Minimal API

Let’s start with an ASP.NET core, minimal API, web API…

  • Create an ASP.NET core Web API project in Visual Studio
  • Enable container support and I’ve chosen Linux OS
  • Ensure Container build type is set to Dockerfile
  • I’m using minimal API so ensure “User Controllers” is not checked

Now let’s just replace Program.cs with the following

using Microsoft.AspNetCore.Diagnostics.HealthChecks;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddHealthChecks();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.MapGet("/echo", (string text) =>
    {
        app.Logger.LogInformation($"C# Echo: {text}");
        return $"Echo: {text}";
    })
    .WithName("Echo")
    .WithOpenApi();

app.MapHealthChecks("/livez");
app.MapHealthChecks("/readyz", new HealthCheckOptions
{
    Predicate = _ => true
});

app.Run();

Docker

Next we need to copy the Dockerfile from the csproj folder to the sln folder – for completeness here’s the Dockerfile generated by Visual Studio (comments removed)

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
USER $APP_UID
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
ARG BUILD_CONFIGURATION=Release
WORKDIR /src
COPY ["EchoService/EchoService.csproj", "EchoService/"]
RUN dotnet restore "./EchoService/EchoService.csproj"
COPY . .
WORKDIR "/src/EchoService"
RUN dotnet build "./EchoService.csproj" -c $BUILD_CONFIGURATION -o /app/build

FROM build AS publish
ARG BUILD_CONFIGURATION=Release
RUN dotnet publish "./EchoService.csproj" -c $BUILD_CONFIGURATION -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "EchoService.dll"]

Note: In Linux port 80 might be locked down, hence we use port 8080 by default.

To build this, run 

docker build -t putridparrot.echo-service:v1 .

Don’t forget to change the name to your preferred name.

and to test this, run

docker run -p 8080:8080 putridparrot.echo-service:v1

and we can text using “http://localhost:8080/echo?text=Putridparrot”

Kubernetes

If all wen well we’ve not tested our application and see it working from a docker image, so now we need to create the deployment etc. for Kubernete’s. Let’s assume you’ve pushed you image to Docker or another container registry such as Azure – I’m call my container registry putridparrotreg.

I’m also not going to use helm at this point as I just want a (relatively) simple yaml file to run from kubectl, so create a deployment.yaml file, we’ll store all the configurations, deployment, service and ingress in this one file jus for simplicity.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: echo
  namespace: dev
  labels:
    app: echo
spec:
  replicas: 1
  selector:
    matchLabels:
      app: echo
  template:
    metadata:
      labels:
        app: echo
    spec:
      containers:
      - name: echo
        image: putridparrotreg/putridparrot.echo-service:v1
        ports:
        - containerPort: 8080
        resources:
          requests:
            memory: "100Mi"
            cpu: "100m"
          limits:
            memory: "200Mi"
            cpu: "200m"
        livenessProbe:
          httpGet:
            path: /livez
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /readyz
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5

---
apiVersion: v1
kind: Service
metadata:
  name: echo-service
  namespace: dev
  labels:
    app: echo
spec:
  type: ClusterIP
  selector:
    app: echo 
  ports:
  - name: http
    port: 80
    targetPort: 8080
    protocol: TCP
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: echo-ingress
  namespace: dev
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: mydomain.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: echo-service
            port:
              number: 80

Don’t forget to change the “host” and image to suit, also this assume you created a namespace “dev” for your app. See Creating a local container registry for information on setting up your own container registry.