Bits of .NET

🔄 Key Takeaways: Master liveness, readiness, and startup probes for graceful deployments and automatic recovery in Kubernetes.

Deployments causing downtime? Probes ensure your pods are ready before receiving traffic.

📋 Complete Probe Configuration

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0  # ✅ Zero downtime!
  template:
    spec:
      containers:
      - name: app
        image: myapp:latest
        ports:
        - containerPort: 80
        
        # 1. Startup Probe - Slow start protection
        startupProbe:
          httpGet:
            path: /health
            port: 80
          failureThreshold: 30
          periodSeconds: 10
          # Total: 30 * 10 = 300 seconds max startup
        
        # 2. Readiness Probe - Traffic control
        readinessProbe:
          httpGet:
            path: /health/ready
            port: 80
          initialDelaySeconds: 5
          periodSeconds: 5
          failureThreshold: 3
        
        # 3. Liveness Probe - Auto-recovery
        livenessProbe:
          httpGet:
            path: /health
            port: 80
          initialDelaySeconds: 30
          periodSeconds: 10
          failureThreshold: 3

💡 .NET Health Checks

// Program.cs
builder.Services.AddHealthChecks()
    .AddDbContextCheck<AppDbContext>("database")
    .AddUrlGroup(new Uri("https://external-api.com"), "external-api")
    .AddCheck("custom");

app.MapHealthChecks("/health", new HealthCheckOptions
{
    ResponseWriter = async (context, report) =>
    {
        context.Response.ContentType = "application/json";
        var result = new
        {
            status = report.Status.ToString(),
            checks = report.Entries.Select(e => new
            {
                name = e.Key,
                status = e.Value.Status.ToString(),
                description = e.Value.Description
            })
        };
        await context.Response.WriteAsJsonAsync(result);
    }
});

📊 Probe Comparison

Probe Type	Purpose	Failure Action	Best For
Startup	Slow start	Restart pod	Large images, migrations
Readiness	Traffic check	Remove from service	Dependencies, warmup
Liveness	Health check	Restart pod	Deadlocks, crashes