Provides a health check implementation that performs ongoing monitoring of an application's dependencies and includes an endpoint that can be called by a load balancer to determine if the application is healthy and thus able to receive traffic.

Add dependency on library.

<dependency>
  <groupId>io.dropwizard.modules</groupId>
  <artifactId>dropwizard-health</artifactId>
  <version>${dropwizard-health.version}</version>
</dependency>

In your application's Configuration class, add a HealthConfiguration object:

public class ExampleConfiguration extends Configuration {
    ...
     
    @Valid
    @NotNull
    @JsonProperty("health")
    private HealthConfiguration healthConfiguration = new HealthConfiguration();
    
    public HealthConfiguration getHealthConfiguration() {
        return healthConfiguration;
    }

    public void setHealthConfiguration(final HealthConfiguration healthConfiguration) {
        this.healthConfiguration = healthConfiguration;
    }
}

Add a HealthCheckBundle to the Bootstrap object in your initialize method:

bootstrap.addBundle(new HealthCheckBundle<ExampleConfiguration>() {
    @Override
    protected HealthConfiguration getHealthConfiguration(final ExampleConfiguration configuration) {
        return configuration.getHealthConfiguration();
    }
});

Configure health checks for any dependencies your application has, such as any databases, caches, queues, etc. Dropwizard modules that support connecting to a dependency will often register a health check automatically.

Define the following health check configurations in your config.yml file:

health:
  delayedShutdownHandlerEnabled: true
  shutdownWaitPeriod: 30s
  healthChecks:
    - name: UserDatabase
      critical: true
    - name: UserNotificationTopic
      critical: false
      schedule:
        checkInterval: 2500ms
        downtimeInterval: 10s
        failureAttempts: 2
        successAttempts: 1
    - name: UserCache
      critical: false

Healthy

$ curl -v https://<hostname>:<port>/health-check
> GET /health-check HTTP/1.1
...
>
< HTTP/1.1 200 OK
< Content-Type: application/json
< Cache-Control: no-store
...
<
{"status": "healthy"}

Not Healthy

$ curl -v https://<hostname>:<port>/health-check
> GET /health-check HTTP/1.1
...
>
< HTTP/1.1 503 Service Unavailable
< Content-Type: application/json
< Cache-Control: no-store
...
<
{"status": "unhealthy"}

Should your service have any dependencies that it needs to perform health checks against that expose either an HTTP or TCP health check interface, you can use the HttpHealthCheck or TcpHealthCheck classes to do so easily.

You will need to register your health check(s) in your Application class run() method.

@Override
public void run(final AppConfiguration configuration, final Environment environment) {
    ...
    environment.healthChecks().register("http-service-dependency", new HttpHealthCheck("http://some-http-dependency.com:8080/health-check"));
}

@Override
public void run(final AppConfiguration configuration, final Environment environment) {
    ...
    environment.healthChecks().register("tcp-service-dependency", new TcpHealthCheck("some-tcp-dependency.com", 443));
}

You might find you need a health check that is a composite of more than one other health check. For instance, consider the case where you have a database and a cache, and if only one of those two are unhealthy, your service can still fulfill a subset of functionality, and thus should not necessarily be marked down.

Let's say that you have a database health check registered under the name UserDatabase and a cache health check under the name UserCache. Below, see an example of how you might create a health check that is a composite of these two checks. Note that there does not exist a CompositeHealthCheck class currently, but it might be a nice addition to this library.

private void registerCompositeHealthCheck(final HealthCheckRegistry healthChecks) {
    final HealthCheck databaseCheck = healthChecks.getHealthCheck("UserDatabase");
    final HealthCheck cacheCheck = healthChecks.getHealthCheck("UserCache");

    final UserHealthCheck userHealthCheck = new UserHealthCheck(databaseCheck, cacheCheck);
    healthChecks.register("UserComposite", userHealthCheck);
}

health:
  delayedShutdownHandlerEnabled: true
  shutdownWaitPeriod: 30s
  healthChecks:
    - name: UserComposite
      critical: true

• Hooks for health status change events.
• Better support for Cloud-native liveness and readiness checks.
• The ability to expose health check data to other modules (for instance, an Admin page may want to show historical health check results).
• More out-of-the-box generally useful health checks implementations, like file-system health checks.