When you enable the /observe endpoints you can configure them to be served on a different port than the application. By default the endpoints are available on the same port as the application. But you can define an extra named socket with another port number in the configuration of the WebServer instance. And in the configuration of the ObserveFeature instance you can define the socket name that should be used for the observe endpoints.

In a previous post you learned how to add information to the /observe/info endpoint. You can also add Git information to the endpoint. For example you can add the Git commit id so you can see check, when the application is running in a production environment, which Git commit for the code was deployed. In order to achieve this you must first generate a properties file with all Git information. The next step is to process this file in your Helidon SE application and add the properties to the /observe/info endpoint.

You can configure a memory health check in Helidon SE. A memory health check will return a status of UP if the memory usage is below a certain threshold percentage and DOWN if the memory usage is above the threshold percentage. The default threshold percentage is 98%. To add the memory health check you need to add the dependency io.helidon.health:helidon-health-checks to your pom.xml file. This dependency contains three health checks: disk space usage, memory usage and dead lock detection.

To configure the memory health check you need to set the configuration property server.features.observe.observers.health.helidon.health.memory.thresholdPercent to the threshold percentage. Alternatively you can set the threshold percentage in your application code.

Suppose you want to return a response based on the Accept header of the request. If the Accept header is application/json you want to return a JSON response and if the Accept header is application/xml you want to return an XML response. You can use the isAccepted(MediaType) of the ServerRequestHeaders class to check if the value of the request header Accept is equal to the specified media type. The method returns true if the media type is defined for the request header Accept and false if not.

In order to convert an object to XML you need to add the dependency com.fasterxml.jackson.dataformat:jackson-dataformat-xml to your pom.xml file:

In Helidon SE you can enable a health check for the disk space usage. If the disk space usage is above a certain threshold then the health check will fail. To enable the disk space health check you need to add the dependency io.helidon.health:helidon-health-checks to your pom.xml file. The dependency contains three health checks: disk space usage, memory usage and dead lock detection.

To configure the disk space health check you need to set the configuration property server.features.observe.observers.health.helidon.health.diskSpace.thresholdPercent to the threshold percentage. Or programmatically set the value in your application code. The default value is 99.999, which means that in real life the health check will not fail. You need to set a lower percentage in order to see the health check fail. For example when you set the value to 95.0 then the health check will fail when the disk space usage is above 95% or less than 5% of the disk space is available. You can also configure the path to check for disk space usage. The default path is the current working directory, but it can be set to another path. You need to set the configuration property server.features.observe.observers.health.helidon.health.diskSpace.path to change the path.

With Helidon SE you can add a health endpoint to your application by simply adding a dependency. In your pom.xml you have to add the dependency io.helidon.webserver.observe:helidon-webserver-observe-health. This adds a new endpoint /health to your application. When your application is up and running the /health endpoint will return the HTTP status code 204 with an empty body. If your application is not healthy then the HTTP status code 503 is returned. In case of an error an HTTP status code 500 is sent to the client.

If you want to see a response with details then you need to set the configuration property server.features.observe.observers.health.details to the value true. Instead of the HTTP status code 204 the status code 200 is returned when our application is healthy. The response contains a JSON object with a status field with the value UP for a healthy response. The response also contains the field checks with an array of detailed information from health checks that are available in our application.

In a previous blog post we learned about the default input sources that are used by Helidon SE. The list of input sources is different based on which artifacts are on the classpath of our application. When we write tests for code in our application that uses the default configuration created by Config.create() we must take into account that different input sources are used. Also here it is based on the artifacts that are on the classpath. That means that different files with configuration data are loaded, eg. a file application-test.conf when we have the artifact helidon-config-hocon and a file application-test.yml if the artifact helidon-config-yaml is on the classpath.

When we use Helidon SE we can use the Config class to pass configuration properties to our application. The static method create() creates a default configuration. The Config class is then configured to support different input sources. This configuration reads configuration properties from the following sources in order:

The last input source behaves differently based on which classes that can parse a configuration file are on the classpath of our application. If we use the helidon-config artifact on the classpath then the configuration file read is application.properties. To read a JSON formatted configuration file we must add the helidon-config-hocon artifact to the classpath. The file that is read is application.json. With the same artifact we can read a HOCON formatted configuration file that is named application.conf. Finally if we add the helidon-config-yaml artifact to the classpath we can read a YAML formatted configuration file that is named application.yaml or application.yml. Helidon SE will only read one configuration file from the classpath with the following order of preference: