/guide-microprofile-health

A guide on how to report and check the health of a microservice with MicroProfile Health: https://openliberty.io/guides/microprofile-health.html

Primary LanguageJavaOtherNOASSERTION

Adding health reports to microservices

Note
 This repository contains the guide documentation source. To view the guide in published form, view it on the Open Liberty website.

Explore how to report and check the health of a microservice with MicroProfile Health.

What you’ll learn

You will learn how to use MicroProfile Health to report the health status of microservices and take appropriate actions based on this report.

MicroProfile Health allows services to report their health, and it publishes the overall health status to a defined endpoint. A service reports UP if it is available and reports DOWN if it is unavailable. MicroProfile Health reports an individual service status at the endpoint and indicates the overall status as UP if all the services are UP. A service orchestrator can then use the health statuses to make decisions.

A service checks its own health by performing necessary self-checks and then reports its overall status by implementing the API provided by MicroProfile Health. A self-check can be a check on anything that the service needs, such as a dependency, a successful connection to an endpoint, a system property, a database connection, or the availability of required resources. MicroProfile offers checks for both liveness and readiness.

You will add liveness and readiness checks to the system and inventory services, which have been provided for you, and implement what is necessary to report health status by using MicroProfile Health.

Try what you’ll build

The finish directory in the root directory of this guide contains two services that are configured to use MicroProfile Health. Feel free to give them a try before you proceed.

To try out the services, navigate to the finish directory and then run the Maven install and liberty:start-server goals to build the services and run them in Open Liberty:

cd finish
mvn install liberty:start-server

The system and inventory services can be found at the following URLs:

Visit the http://localhost:9080/health URL to see the overall health status of the application, as well as the aggregated data of the liveness and readiness checks. Two checks show the state of the system service, and the other two checks show the state of the inventory service. As you might expect, both services are in the UP state, and the overall health status of the application is in the UP state.

You can also access the /health/ready endpoint by visiting the http://localhost:9080/health/ready URL to view the data from the readiness health checks. Similarly, access the /health/live endpoint by visiting the http://localhost:9080/health/live URL to view the data from the liveness health checks.

When you are done checking out the services, stop the Open Liberty server by running the following command:

mvn liberty:stop-server

Adding health checks to microservices

Navigate to the start directory to begin.

A health report will be generated automatically for all services that enable MicroProfile Health. The mpHealth feature has already been enabled for you in the src/main/liberty/config/server.xml file.

All services must provide an implementation of the HealthCheck interface, which will be used to verify their health. MicroProfile Health offers health checks for both readiness and liveness. A readiness check allows third-party services, such as Kubernetes, to determine whether a microservice is ready to process requests. For example, a readiness check might check dependencies, such as database connections. A liveness check allows third-party services to determine whether a microservice is running. If the liveness check fails, the application can be terminated. For example, a liveness check might fail if the application runs out of memory.

server.xml

link:finish/src/main/liberty/config/server.xml[role=include]

Adding health checks to the system service

Create the SystemReadinessCheck class.
src/main/java/io/openliberty/guides/system/SystemReadinessCheck.java

SystemReadinessCheck.java

link:finish/src/main/java/io/openliberty/guides/system/SystemReadinessCheck.java[role=include]

The @Readiness annotation indicates that this particular bean is a readiness health check procedure. By pairing this annotation with the ApplicationScoped context from the Contexts and Dependency Injections API, the bean is discovered automatically when the http://localhost:9080/health endpoint receives a request.

The call() method is used to return the health status of a particular service. In this case, you are simply checking if the server name is defaultServer and returning UP if it is, and DOWN otherwise. The HealthCheckResponse.named() method is used to indicate what service the health check is done for. Overall, this is a very simple implementation of the call() method. In a real development environment, you would want to orchestrate much more meaningful health checks.

Create the SystemLivenessCheck class.
src/main/java/io/openliberty/guides/system/SystemLivenessCheck.java

SystemLivenessCheck.java

link:finish/src/main/java/io/openliberty/guides/system/SystemLivenessCheck.java[role=include]

The @Liveness annotation indicates that this is a liveness health check procedure. In this case, you are checking the heap memory usage. If more than 90% of the maximum memory is being used, a status of DOWN will be returned.

Adding health checks to the inventory service

Create the InventoryReadinessCheck class.
src/main/java/io/openliberty/guides/inventory/InventoryReadinessCheck.java

InventoryReadinessCheck.java

link:finish/src/main/java/io/openliberty/guides/inventory/InventoryReadinessCheck.java[role=include]

This time, you are checking whether or not the service is in maintenance or if it’s down. For simplicity, the custom io_openliberty_guides_inventory_inMaintenance MicroProfile Config property defined in the resources/CustomConfigSource.json file is used to indicate whether the service is in maintenance or not. This file has already been created for you. To check if the service is down, simply make a HTTP GET request to the system service and check the status returned by the response. You make a GET request to the system service rather than the inventory service because the inventory service depends on the system service. In other words, the inventory service wouldn’t work if the system service is down. If the status is not 200, then the service is not running. Based on these two factors, the isHealthy() method returns whether or not the inventory service is healthy.

If you are curious about the injected inventoryConfig object or if you want more information on MicroProfile Config, see Configuring microservices.

Create the InventoryLivenessCheck class.
src/main/java/io/openliberty/guides/inventory/InventoryLivenessCheck.java

InventoryLivenessCheck.java

link:finish/src/main/java/io/openliberty/guides/inventory/InventoryLivenessCheck.java[role=include]

As with the system liveness check, you are checking the heap memory usage. If more than 90% of the maximum memory is being used, a DOWN status is returned.

CustomConfigSource.json

link:finish/resources/CustomConfigSource.json[role=include]

While the server is running, navigate to the http://localhost:9080/health URL to find the aggregated liveness and readiness health reports on the two services.

You can also navigate to the http://localhost:9080/health/ready URL to view the readiness health report, or the http://localhost:9080/health/live URL to view the liveness health report.

Put the inventory service in maintenance by setting the io_openliberty_guides_inventory_inMaintenance property to true in the resources/CustomConfigSource.json file. Because this configuration file is picked up dynamically, simply refresh the http://localhost:9080/health URL you will see that the state of the inventory service has changed to DOWN. The overall state of the application has also changed to DOWN as a result. Point to the http://localhost:9080/inventory/systems URL to verify that the inventory service is indeed in maintenance. Set the io_openliberty_guides_inventory_inMaintenance property back to false once you are done.

CustomConfigSource.json

link:finish/resources/CustomConfigSource.json[role=include]

Testing health checks

You will implement several test methods, testIfServicesAreUp(), testReadiness(), testLiveness(), and testIfInventoryServiceIsDown(), to validate the health of the system and inventory services.

Create the HealthTest class.
src/test/java/it/io/openliberty/guides/health/HealthTest.java

HealthTest.java

link:finish/src/test/java/it/io/openliberty/guides/health/HealthTest.java[role=include]

Let’s break down the test cases:

  • The testIfServicesAreUp() test case compares the generated health report with the actual status of the services.

  • The testReadiness() test case compares the generated health report for the readiness checks with the actual status of the services.

  • The testLiveness() test case compares the generated health report for the liveness checks with the actual status of the services.

  • The testIfInventoryServiceIsDown() test case puts the inventory service in maintenance by setting the io_openliberty_guides_inventory_inMaintenance property to true and comparing the generated health report with the actual status of the services.

A few more tests have been included to verify the basic functionalitiy of the system and inventory services. They can be found under the src/test/java/it/io/openliberty/guides/inventory/InventoryEndpointTest.java and src/test/java/it/io/openliberty/guides/system/SystemEndpointTest.java files. If a test failure occurs, then you might have introduced a bug into the code. These tests will run automatically as a part of the Maven build process when you run the mvn install command. You can also run these tests separately from the build by using the mvn verify command, but first make sure that the server is stopped.

CustomConfigSource.json

link:finish/resources/CustomConfigSource.json[role=include]

InventoryEndpointTest.java

link:finish/src/test/java/it/io/openliberty/guides/inventory/InventoryEndpointTest.java[role=include]

SystemEndpointTest.java

link:finish/src/test/java/it/io/openliberty/guides/system/SystemEndpointTest.java[role=include]
-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running it.io.openliberty.guides.health.HealthTest
Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 3.504 sec - in it.io.openliberty.guides.health.HealthTest
Running it.io.openliberty.guides.inventory.InventoryEndpointTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.326 sec - in it.io.openliberty.guides.inventory.InventoryEndpointTest
Running it.io.openliberty.guides.system.SystemEndpointTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.011 sec - in it.io.openliberty.guides.system.SystemEndpointTest

Results :

Tests run: 6, Failures: 0, Errors: 0, Skipped: 0

To see whether the tests detect a failure, manually change the configuration of io_openliberty_guides_inventory_inMaintenance from false to true in the resources/CustomConfigSource.json file. Re-run the Maven build. You will see a test failure occur because the initial status of the inventory service is DOWN.

Great work! You’re done!

You just learned how to add health checks to report the states of microservices by using MicroProfile Health in Open Liberty. Then, you wrote tests to validate the generated health report.

Feel free to try one of the related MicroProfile guides. They demonstrate additional technologies that you can learn and expand on top of what you built here.