Health checks

Health checks provide availability and state information about an app. Health checks are often exposed as HTTP endpoints, but can also be used internally by the app to write logs or perform other tasks based on the current health. Health checks are typically used in combination with an external monitoring service or container orchestrator to check the status of an app.

Two types of health checks

Aspire uses health checks in two distinct contexts. Understanding the difference is crucial:

Health check type	Where it runs	What it checks	Used for
AppHost resource checks	AppHost project	”Is my dependency ready?”	Startup orchestration, WaitFor()
Service endpoint checks	Your application	”Am I healthy?”	Load balancers, Kubernetes probes

Key insight

AppHost health checks answer: “Should I start services that depend on this resource?” Service endpoint health checks answer: “Should traffic be sent to this instance?”

Readiness vs. Liveness

The two endpoint types serve different purposes:

• Readiness (/health) - “Am I ready to receive traffic?” Checks that dependencies are connected, initialization is complete, and the service can handle requests. A failing readiness check means “don’t send me traffic yet.”

• Liveness (/alive) - “Am I still running?” Checks that the process hasn’t deadlocked or crashed. A failing liveness check means “restart me.”

Aspire health check endpoints

Aspire exposes two default health check HTTP endpoints in Development environments when the AddServiceDefaults and MapDefaultEndpoints methods are called from the Program.cs file:

• The /health endpoint indicates if the app is running normally where it’s ready to receive requests. All health checks must pass for app to be considered ready to accept traffic after starting.

  HTTP

  GET /health

  The /health endpoint returns an HTTP status code 200 and a text/plain value of Healthy when the app is healthy.

• The /alive indicates if an app is running or has crashed and must be restarted. Only health checks tagged with the live tag must pass for app to be considered alive.

  HTTP

  GET /alive

  The /alive endpoint returns an HTTP status code 200 and a text/plain value of Healthy when the app is alive.

The AddServiceDefaults and MapDefaultEndpoints methods also apply various configurations to your app beyond just health checks, such as OpenTelemetry and service discovery configurations.

Non-development environments

In non-development environments, the /health and /alive endpoints are disabled by default. If you need to enable them, its recommended to protect these endpoints with various routing features, such as host filtering and/or authorization. For more information, see Health checks in ASP.NET Core.

Additionally, it may be advantageous to configure request timeouts and output caching for these endpoints to prevent abuse or denial-of-service attacks. To do so, consider the following modified AddDefaultHealthChecks method:

C#

Extensions.cs

public static IHostApplicationBuilder AddDefaultHealthChecks(
    this IHostApplicationBuilder builder)
{
    builder.Services.AddRequestTimeouts(
        configure: static timeouts =>
            timeouts.AddPolicy("HealthChecks", TimeSpan.FromSeconds(5)));

    builder.Services.AddOutputCache(
        configureOptions: static caching =>
            caching.AddPolicy("HealthChecks",
            build: static policy => policy.Expire(TimeSpan.FromSeconds(10))));

    builder.Services.AddHealthChecks()
        // Add a default liveness check to ensure app is responsive
        .AddCheck("self", () => HealthCheckResult.Healthy(), ["live"]);

    return builder;
}

Go

Go — health.go

package main

import (
    "net/http"
)

// healthHandler returns HTTP 200 when the app is healthy.
func healthHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/plain")
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("Healthy"))
}

// aliveHandler returns HTTP 200 when the app is running.
func aliveHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/plain")
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("Healthy"))
}

Python

Python — health.py

from fastapi import FastAPI

app = FastAPI()

@app.get("/health")
async def health():
    """Readiness check — returns 200 when the app is ready for traffic."""
    return {"status": "Healthy"}

@app.get("/alive")
async def alive():
    """Liveness check — returns 200 when the app is running."""
    return {"status": "Healthy"}

TypeScript

TypeScript — health.ts

import express from 'express';

const app = express();

// Readiness check — returns 200 when the app is ready for traffic
app.get('/health', (req, res) => {
  res.type('text/plain').send('Healthy');
});

// Liveness check — returns 200 when the app is running
app.get('/alive', (req, res) => {
  res.type('text/plain').send('Healthy');
});

The preceding code:

• Adds a timeout of 5 seconds to the health check requests with a policy named HealthChecks.
• Adds a 10-second cache to the health check responses with a policy named HealthChecks.

Now consider the updated MapDefaultEndpoints method:

C#

Extensions.cs

public static WebApplication MapDefaultEndpoints(
    this WebApplication app)
{
    var healthChecks = app.MapGroup("");

    healthChecks
        .CacheOutput("HealthChecks")
        .WithRequestTimeout("HealthChecks");

    // All health checks must pass for app to be
    // considered ready to accept traffic after starting
    healthChecks.MapHealthChecks("/health");

    // Only health checks tagged with the "live" tag
    // must pass for app to be considered alive
    healthChecks.MapHealthChecks("/alive", new()
    {
        Predicate = static r => r.Tags.Contains("live")
    });

    return app;
}

Go

Go — health.go

package main

import (
    "net/http"
    "time"
)

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/health", healthHandler)
    mux.HandleFunc("/alive", aliveHandler)

    server := &http.Server{
        Addr:         ":8080",
        Handler:      mux,
        ReadTimeout:  5 * time.Second,
        WriteTimeout: 5 * time.Second,
    }

    server.ListenAndServe()
}

Python

Python — main.py

import uvicorn

# The /health and /alive endpoints defined above
# are automatically available when running the FastAPI app
if __name__ == "__main__":
    uvicorn.run("health:app", host="0.0.0.0", port=8080)

TypeScript

TypeScript — server.ts

// The /health and /alive endpoints defined above
// are automatically available when the Express app starts
app.listen(8080, () => {
  console.log('Server running on port 8080');
});

The preceding code:

• Groups the health check endpoints under the / path.
• Caches the output and specifies a request time with the corresponding HealthChecks policy.

In addition to the updated AddDefaultHealthChecks and MapDefaultEndpoints methods, you must also add the corresponding services for both request timeouts and output caching.

In the appropriate consuming app’s entry point (usually the Program.cs file), add the following code:

C#

// Wherever your services are being registered.
// Before the call to Build().
builder.Services.AddRequestTimeouts();
builder.Services.AddOutputCache();

var app = builder.Build();

// Wherever your app has been built, before the call to Run().
app.UseRequestTimeouts();
app.UseOutputCache();

app.Run();

Go

Go — main.go

import (
   "context"
   "net/http"
   "time"
 )

// In Go, use context timeouts for request timeout control
func healthHandler(w http.ResponseWriter, r *http.Request) {
   ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
   defer cancel()
   // Use the ctx for your health check logic
   _ = ctx
 }

Python

Python — main.py

from starlette.middleware import Middleware
from starlette.middleware.base import BaseHTTPMiddleware
import asyncio

# FastAPI supports request timeouts via middleware or
# server-level configuration (e.g., uvicorn --timeout-keep-alive)

TypeScript

TypeScript — server.ts

// In Express, use middleware for request timeouts
import timeout from 'connect-timeout';

app.use('/health', timeout('5s'));
app.use('/alive', timeout('5s'));

For more information, see Request timeouts middleware in ASP.NET Core and Output caching middleware in ASP.NET Core.

Integration health checks

Aspire integrations can also register additional health checks for your app. These health checks contribute to the returned status of the /health and /alive endpoints. For example, the Aspire PostgreSQL integration automatically adds a health check to verify the following conditions:

• A database connection could be established.
• A database query could be executed successfully.

If either of these operations fail, the corresponding health check also fails.

Configure health checks

You can disable health checks for a given integration using one of the available configuration options. Aspire integrations support Microsoft.Extensions.Configurations to apply settings through config files such as appsettings.json:

JSON — appsettings.json

{
  "Aspire": {
    "Npgsql": {
      "DisableHealthChecks": true
    }
  }
}

You can also use an inline delegate to configure health checks:

C#

C# — Program.cs

builder.AddNpgsqlDbContext<MyDbContext>(
    "postgresdb",
    static settings => settings.DisableHealthChecks  = true);

Go

Go — main.go

package main

import (
    "net/http"
    "os"
    "context"
    "github.com/jackc/pgx/v4"
)

connStr := os.Getenv("ConnectionStrings__postgresdb")
conn, err := pgx.Connect(context.Background(), connStr)

// Health endpoint returns healthy without checking
// the database. In Go, health checks are explicit —
// omit a database ping to disable them.
http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("Healthy"))
})

Python

Python — app.py

import os
import psycopg2

if __name__ == "__main__":
    uvicorn.run("health:app", host="0.0.0.0", port=8080)

conn_str = os.environ.get("ConnectionStrings__postgresdb")
conn = psycopg2.connect(conn_str)

# Health endpoint returns healthy without checking
# the database. In Python, health checks are explicit —
# omit a database ping to disable them.
@app.get("/health")
async def health():
    return {"status": "Healthy"}

TypeScript

TypeScript — app.ts

import pg from 'pg';
import express from 'express';

const app = express();

const pool = new pg.Pool({
    connectionString: process.env.ConnectionStrings__postgresdb,
});

// Health endpoint returns healthy without checking
// the database. In TypeScript, health checks are explicit —
// omit a database ping to disable them.
app.get('/health', (req, res) => {
    res.type('text/plain').send('Healthy');
});

AppHost resource health checks

AppHost resource health checks are different from the health check endpoints described earlier. These health checks are configured in the AppHost project and determine the readiness of resources from the orchestrator’s perspective. They’re particularly important for controlling when dependent resources start via the WaitFor functionality and are displayed in the Aspire dashboard.

Resource readiness with health checks

When a resource has health checks configured, the AppHost uses them to determine if the resource is ready before starting dependent resources. If no health checks are registered for a resource, the AppHost waits for the resource to be in the Running state.

HTTP health checks for resources

For resources that expose HTTP endpoints, you can add health checks that poll specific paths:

C#

C# — AppHost.cs

var builder = DistributedApplication.CreateBuilder(args);

var catalogApi = builder.AddContainer("catalog-api", "catalog-api")
                        .WithHttpEndpoint(targetPort: 8080)
                        .WithHttpHealthCheck("/health");

builder.AddProject<Projects.WebApp>("webapp")
       .WithReference(catalogApi)
       .WaitFor(catalogApi); // Waits for /health to return HTTP 200

TypeScript

TypeScript — apphost.ts

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

const catalogApi = await builder
  .addContainer('catalog-api', { image: 'catalog-api', tag: 'latest' })
  .withHttpEndpoint({ targetPort: 8080 })
  .withHttpHealthCheck('/health');

await builder
  .addProject('webapp', './WebApp/WebApp.csproj')
  .withReference(catalogApi)
  .waitFor(catalogApi);

await builder.build().run();

The WithHttpHealthCheck method can also be applied to project resources:

C#

C# — AppHost.cs

var backend = builder.AddProject<Projects.Backend>("backend")
                     .WithHttpHealthCheck("/health");

builder.AddProject<Projects.Frontend>("frontend")
       .WithReference(backend)
       .WaitFor(backend);

TypeScript

TypeScript — apphost.ts

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

const backend = await builder
  .addProject('backend', './Backend/Backend.csproj')
  .withHttpHealthCheck('/health');

await builder
  .addProject('frontend', './Frontend/Frontend.csproj')
  .withReference(backend)
  .waitFor(backend);

await builder.build().run();

Custom resource health checks

You can create custom health checks for more complex readiness scenarios. Start by defining the health check in the AppHost’s service collection, then associate it with resources:

C#

C# — AppHost.cs

var builder = DistributedApplication.CreateBuilder(args);

var startAfter = DateTime.Now.AddSeconds(30);

builder.Services.AddHealthChecks().AddCheck("mycheck", () =>
    {
        return DateTime.Now > startAfter
            ? HealthCheckResult.Healthy()
            : HealthCheckResult.Unhealthy();
    });

var pg = builder.AddPostgres("pg")
    .WithHealthCheck("mycheck");

builder.AddProject<Projects.MyApp>("myapp")
    .WithReference(pg)
    .WaitFor(pg); // Waits for both the Postgres container to be running
                  // AND the custom "mycheck" health check to be healthy

TypeScript

Note

Custom health check registration via builder.services.addHealthChecks() is not yet available in the TypeScript AppHost SDK. Use withHttpHealthCheck for HTTP-based health checks instead.

TypeScript — apphost.ts

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

const pg = await builder
  .addPostgres('pg')
  .withHttpHealthCheck('/health');

await builder
  .addProject('myapp', './MyApp/MyApp.csproj')
  .withReference(pg)
  .waitFor(pg);

await builder.build().run();

The AddCheck method registers the health check, and WithHealthCheck associates it with specific resources. For more details about creating and registering custom health checks, see Create health checks.

Dashboard integration

Resource health check status is displayed in the Aspire dashboard, providing real-time visibility into resource readiness. When resources are waiting for health checks to pass, the dashboard shows the current status and any failure details.