README.adoc

../shared-doc/attributes.adoc

microprofile-health: MicroProfile Health QuickStart

The microprofile-health quickstart demonstrates the use of the MicroProfile Health specification in {productName}.

What is it?

MicroProfile Health allows applications to provide information about their state to external viewers which is typically useful in cloud environments where automated processes must be able to determine whether the application should be discarded or restarted.

Architecture

In this quickstart, we have a simple REST application that exposes MicroProfile Health functionalities at the /health/live, /health/ready, and /health/started endpoints according to the specification.

../shared-doc/system-requirements.adoc

../shared-doc/use-of-jboss-home-name.adoc

../shared-doc/start-the-standalone-server.adoc

Solution

We recommend that you follow the instructions that create the application step by step. However, you can also go right to the completed example which is available in this directory.

../shared-doc/build-and-deploy-the-quickstart.adoc

Running the health check

The {productName} server directly exposes three REST endpoints:

• /health/live - The application is up and running.

• /health/ready - The application is ready to serve requests.

• /health/started - The application is started allowing switch to liveness check.

• /health - Accumulating all health check procedures in the application.

To check that the {productName} is working as expected:

• access the http://localhost:9990/health/live endpoint using your browser or curl http://localhost:9990/health/live

All of the health REST endpoints return a simple JSON object with two fields:

• status — the overall result of all the health check procedures

• checks — an array of individual checks

The general status of the health check is computed as a logical AND of all the declared health check procedures.

Note	Similarly, you can access http://localhost:9990/health/ready, http://localhost:9990/health/started, and http://localhost:9990/health

Congratulations! You successfully deployed and run this quickstart. If you wish to create the application step by step you can follow the subsequent sections.

../shared-doc/undeploy-the-quickstart.adoc

../shared-doc/run-arquillian-tests.adoc

../shared-doc/run-the-quickstart-in-jboss-developer-studio.adoc

Creating the Maven Project

mvn archetype:generate \
    -DgroupId=org.wildfly.quickstarts \
    -DartifactId=microprofile-health \
    -DinteractiveMode=false \
    -DarchetypeGroupId=org.apache.maven.archetypes \
    -DarchetypeArtifactId=maven-archetype-quickstart
cd microprofile-health

Open the project in your favourite IDE.

Open the generated pom.xml.

The first thing to do is to change the packaging to war as this is required by the IDEs to recognize the application as a deployment:

<packaging>war</packaging>

Note	For non-IDE deployments, the plain jar packaging is sufficient for the MicroProfile Health applications.

Next we need to setup our dependencies. Add the following section to your pom.xml:

<dependencyManagement>
  <dependencies>
    <!-- importing the microprofile BOM adds MicroProfile specs -->
    <dependency>
      <groupId>org.wildfly.bom</groupId>
      <artifactId>wildfly-microprofile</artifactId>
      <version>{versionMicroprofileBom}</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

Now we need to add the following two dependencies:

<!-- Import the MicroProfile Health API, we use provided scope as the API is included in the server -->
<dependency>
  <groupId>org.eclipse.microprofile.health</groupId>
  <artifactId>microprofile-health-api</artifactId>
  <scope>provided</scope>
</dependency>
<!-- Import the CDI API, we use provided scope as the API is included in the server -->
<dependency>
  <groupId>jakarta.enterprise</groupId>
  <artifactId>jakarta.enterprise.cdi-api</artifactId>
  <scope>provided</scope>
</dependency>

Note	Because MicroProfile Health requires that all health checks are defined as CDI beans we need to also include the CDI API dependency.

Both dependencies can have provided scope. The versions are taken from the above defined BOM.

As we are going to be deploying this application to the {productName} server, let’s also add a maven plugin that will simplify the deployment operations (you can replace the generated build section):

<build>
  <!-- Set the name of the archive -->
  <finalName>${project.artifactId}</finalName>
  <plugins>
    <!-- Allows to use mvn wildfly:deploy -->
    <plugin>
      <groupId>org.wildfly.plugins</groupId>
      <artifactId>wildfly-maven-plugin</artifactId>
    </plugin>
  </plugins>
</build>

../shared-doc/setup-repositories.adoc

Now we are ready to start working with MicroProfile Health.

Creating your first health check

In this section, we create our first simple health check procedure.

Create the org.wildfly.quickstarts.microprofile.health.SimpleHealthCheck class:

package org.wildfly.quickstarts.microprofile.health;

import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.Liveness;

import jakarta.enterprise.context.ApplicationScoped;

@Liveness
@ApplicationScoped
public class SimpleHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.up("Simple health check");
    }
}

As you can see health check procedures are defined as implementations of the HealthCheck interface which are defined as CDI beans with the one of the following CDI qualifiers:

• @Liveness - the liveness check accessible at /health/live

• @Readiness - the readiness check accessible at /health/ready

• @Startup - the readiness check accessible at /health/started

HealthCheck is a functional interface whose single method call returns a HealthCheckResponse object which can be easily constructed by the fluent builder API shown in the example.

Now it’s time to build and deploy our application that contains this health check to the {productName} server.

WARN: Make sure your {productName} server is started.

$ mvn clean package wildfly:deploy

Now we can simply repeat the request to http://localhost:9990/health/live by refreshing your browser window or by using curl http://localhost:9990/health/live. Because we defined our health check to be a liveness procedure (with @Liveness qualifier) the new health check procedure is now present in the checks array.

Congratulations! You’ve created your first health check procedure. Let’s continue by exploring what else can be done with the MicroProfile Health specification.

Adding a readiness health check procedure

In the previous section, we created a simple liveness health check procedure which states whether our application is running or not. In this section, we will create a readiness health check which will be able to state whether our application is able to process requests.

We will create another health check procedure that simulates a connection to an external service provider such as a database. For starters, we will always return the response indicating the application is ready.

Create org.wildfly.quickstarts.microprofile.health.DatabaseConnectionHealthCheck class:

package org.wildfly.quickstarts.microprofile.health;

import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.Readiness;

import jakarta.enterprise.context.ApplicationScoped;

@Readiness
@ApplicationScoped
public class DatabaseConnectionHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.up("Database connection health check");
    }
}

Now you can redeploy your application:

$ mvn clean package wildfly:deploy

If you now rerun the health check at http://localhost:9990/health/live the checks array will contain only the previously defined SimpleHealthCheck as it is the only check defined with the @Liveness qualifier. However, if you access http://localhost:9990/health/ready (in the browser or with curl http://localhost:9990/health/ready) you will see only the Database connection health check as it is the only health check defined with the @Readiness qualifier as the readiness health check procedure.

Note	If you access http://localhost:9990/health you will get back both checks.

More information about which health check procedures should be used in which situation is detailed in the MicroProfile Health specification. Generally, the liveness procedures determine whether the application should be restarted while readiness procedures determine whether it makes sense to contact the application with requests.

Startup health checks

Startup health checks are used in cloud environments to define checks that should respond UP before the liveness checks start to be called. This is useful in cases of slow container startups so the container won’t get prematurely restarted if liveness is called before the container is fully initialized. These checks are defined in the same way as liveness or readiness checks but with the @Startup CDI qualifier. The HTTP endpoint exposed for the startup checks is available at /health/started. For simplicity, we will not include code example in this quickstart.

Negative health check procedures

In this section, we extend our Database connection health check with the option of stating that our application is not ready to process requests as the underlying database connection cannot be established. For simplicity reasons, we only determine whether the database is accessible or not by a configuration property.

To use MicroProfile Config configuration values we first need to add the Config API dependency to our application:

<!-- Import the MicroProfile Config API, we use provided scope as the API is included in the server -->
<dependency>
  <groupId>org.eclipse.microprofile.config</groupId>
  <artifactId>microprofile-config-api</artifactId>
  <scope>provided</scope>
</dependency>

Update the org.wildfly.quickstarts.microprofile.health.DatabaseConnectionHealthCheck class:

package org.wildfly.quickstarts.microprofile.health;

import org.eclipse.microprofile.config.inject.ConfigProperty;
import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.HealthCheckResponseBuilder;
import org.eclipse.microprofile.health.Readiness;

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.inject.Inject;

@Readiness
@ApplicationScoped
public class DatabaseConnectionHealthCheck implements HealthCheck {

    @Inject
    @ConfigProperty(name = "database.up", defaultValue = "false")
    private boolean databaseUp;

    @Override
    public HealthCheckResponse call() {

        HealthCheckResponseBuilder responseBuilder = HealthCheckResponse.named("Database connection health check");

        try {
            simulateDatabaseConnectionVerification();
            responseBuilder.up();
        } catch (IllegalStateException e) {
            // cannot access the database
            responseBuilder.down();
        }

        return responseBuilder.build();
    }

    private void simulateDatabaseConnectionVerification() {
        if (!databaseUp) {
            throw new IllegalStateException("Cannot contact database");
        }
    }
}

Redeploy your application:

$ mvn clean package wildfly:deploy

If you now rerun the readiness health check (at http://localhost:9990/health/ready) the overall status should be DOWN. You can also check the liveness check at http://localhost:9990/health/live which will return the overall status UP because it isn’t influenced by the readiness checks.

As we shouldn’t leave this application with a readiness check in a DOWN state you can add database.up=true in src/main/resources/META-INF/microprofile-config.properties and redeploy the application. The readiness health check should be up again.

Adding user-specific data to the health check response

In previous sections, we saw how to create simple health checks with only the minimal attributes, namely, the health check name and its status (UP or DOWN). However, the MicroProfile specification also provides a way for the applications to supply arbitrary data in the form of key-value pairs sent to the consuming end. This can be done by using the withData(key, value) method of the health check response builder API.

Let’s create a new health check procedure org.wildfly.quickstarts.microprofile.health.DataHealthCheck:

package org.wildfly.quickstarts.microprofile.health;

import org.eclipse.microprofile.health.Liveness;
import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;

import jakarta.enterprise.context.ApplicationScoped;

@Liveness
@ApplicationScoped
public class DataHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.named("Health check with data")
                .up()
                .withData("foo", "fooValue")
                .withData("bar", "barValue")
                .build();
    }
}

If you redeploy and rerun the liveness health check procedure by accessing the /health/live endpoint you can see that the new health check Health check with data is present in the checks array. This check contains a new attribute called data which is a JSON object consisting of the properties we have defined in our health check procedure.

This functionality is specifically useful in failure scenarios where you can pass the error along with the health check response.

        try {
            simulateDatabaseConnectionVerification();
            responseBuilder.up();
        } catch (IllegalStateException e) {
            // cannot access the database
            responseBuilder.down()
                    .withData("error", e.getMessage()); // pass the exception message
        }

../shared-doc/build-and-run-the-quickstart-with-bootable-jar.adoc

Conclusion

MicroProfile Health provides a way for your application to distribute information about its healthiness state to state whether or not it is able to function properly. Liveness checks are utilized to tell whether the application should be restarted. Readiness checks are used to tell whether the application is able to process requests. And last but not least, startup checks are useful if your container has a slow startup to prevent premature restarts if the liveness probes are called too soon.

Congratulations! You have reached the end of this tutorial. You can find more information about the MicroProfile Health in the specification github repository.