Health Checks

Camel provides support to probe the state of an integration via a pluggable Health Check strategy based on the following concepts:

  • HealthCheck: represents a health check and defines its basic contract.

  • HealthCheckResponse: represents a health check invocation response.

  • HealthCheckConfiguration: a basic configuration object that holds some basic settings like the minimum delay between calls, the number of times a service may be reported as unhealthy before marking the check as failed; besides these simple options, the check implementation is responsible for implementing further limitations where needed.

  • HealthCheckRegistry: a registry for health checks. There is a single default implementation and end users should really not implement their own.

  • HealthCheckRepository: a simple interface to define health check providers. By default there is one that grabs all the checks available in the registry so you can add your own check i.e. instantiating your bean in spring/spring-boot; components can provide their own repository.

Health checks out of the box

Camel provides the following health checks out of the box:

  • context - A HealthCheck which performs check whether the CamelContext is started. This can be used for readiness checks; to know when Camel is fully started and ready to handle traffic.

  • routes - A HealthCheckRegistry which discovers all the available routes in CamelContext and checks whether they are all started. This can be used for readiness checks; to know when Camel is fully started and ready to handle traffic. Combining with the supervised RouteController this allows to perform readiness check for routes that are under supervising, such as troublesome routes that may not start up the first time, and are retried to be started in the background with backoff delays.

  • consumers A HealthCheckRegistry which discovers all the consumers from all the routes in CamelContext enabling fine-grained checks for the route input. This means if the consumer is failing to poll new messages then the health check can detect this and report as un-healthy. Note that the consumer will be DOWN during its initialization and until at least one poll run has been executed, to know whether that poll was a success or not. And if the poll was a success then the consumer is UP. This is on purpose to avoid having the health check to be initially UP and then after first poll run then DOWN again because the consumer cannot poll from external system; which causes the health check to be flaky.

  • registry - A HealthCheckRegistry which discovers all the available custom HealthCheck instances in the Registry.

IDs

A HealthCheck and HealthCheckRegistry has an ID. The ID has the name syntax name-health-check, or name-health-check-repository. With the suffix -health-check or -health-check-repository. When looking up or resolving by IDs then the shorthand name can be used.

For example context-health-check is the ID but can also be used by its shorthand context.

The ID of the consumer health checks is the route id with consumer: as prefix, i.e. if the route is named foo, then the ID is consumer:foo.

Readiness and Liveness

A health check is by default usable for both readiness and liveness checks.

To specify a custom health check as only usable for liveness checks, you would need to turn off readiness, by overriding the isReadiness method and return false.

@Override
public boolean isReadiness() {
    return false;
}

Configuring health-check

Camel supports via camel-main to configure health-checks from configuration files. This is possible for runtimes that leverage camel-main such as Camel on Spring Boot, or Camel K.

Camel will automatically enable context, routes, consumers, and registry health-checks if camel-health is detected on the classpath. They are all enabled by default (context is always enabled and cannot be disabled). However, you can configure them, for example to turn them off:

# global option to turn health-check off (will not install health-check)
### camel.health.enabled=false

# allows to enable or disable health-checks from startup
# for example to only use context health-check
camel.health.routesEnabled=false
camel.health.consumersEnabled=false
camel.health.registryEnabled=false

Excluding health-checks

By default, all enabled health-checks are invoked by Camel when check the health status.

It is possible to specify checks that should be excluded, for example a specific route by the route-id.

camel.health.exclude-pattern = myroute

You can specify multiple patterns (and use wildcards) such as:

camel.health.exclude-pattern = myroute,foo,bar*

Turning off consumer level health-checks

If routes health check is enabled then they will execute consumer health-checks as well as part of an aggregated response.

The consumer checks can be turned off, to only use the route level checks (status of the route)

camel.health.consumersEnabled=false

You can also turn off individual consumers by prefixing the ID with consumer: and the route id:

camel.health.exclude-pattern = consumer:myroute*

which will turn off checks for all consumers on routes that starts with myroute in the route ID.

JMX management

The health check is manageable via JMX (requires camel-management JAR on the classpath). You can find the DefaultHealthCheck MBean under the health node in the Camel JMX tree.

This MBean allows at runtime to manage health-checks where you can enable and disable checks based on their IDs. As well have the latest status whether the overall health check is healthy or not. The MBean also allows invoking health checks based on IDs (or all of them).

Configuring level of details in the health check responses

The option exposureLevel sets the level of details to exposure as result of invoking health checks.

There are the following levels:

  • full - The full level will include all details and status from all the invoked health checks.

  • default - The default level will report UP if everything is okay, and only include detailed information for health check that was DOWN.

  • oneline - The oneline level will only report either UP or DOWN.

You can specify multiple patterns (and use wildcards) such as:

For example to only report either as UP or DOWN then use:

camel.health.exposure-level = oneline

Enriching and controlling health check responses

Each health check that is invoked will gather details about the result using HealthCheckResultBuilder.

To allow enriching and manipulating the result, then you can use HealthCheckResultStrategy to plug in a custom bean that can process the result, and change state, add information, remove unwanted information, etc. on the result builder.

The custom bean should be registered to the Camel Registry to be discovered by camel-health. Only one instance of the bean is allowed.

Invoking health checks

You can invoke the health checks from Java by using the org.apache.camel.health.HealthCheckHelper which has APIs to easily invoke all the health checks and gather their results, or filter out unwanted checks, or invoke only the readiness or liveness checks.

The health checks can also be invoked from JMX.

Writing a custom health check

There are a limited number of health checks provided by Camel out of the box, so you may need to write your own check which you can do by implementing the HealthCheck interface or by extending AbstractHealthCheck which provides some useful methods.

To make the health-check discoverable you should annotate the class with @HealthCheck and the name-check syntax.

import org.apache.camel.spi.annotations.HealthCheck;
import org.apache.camel.impl.health.AbstractHealthCheck;

@HealthCheck("my-check")
public final class MyHealthCheck extends AbstractHealthCheck {

    public MyHealthCheck() {
        super("myapp", "my-check");
    }

    @Override
    protected void doCall(HealthCheckResultBuilder builder, Map<String, Object> options) {
        // Default value
        builder.unknown();

        // Add some details to the check result
        builder.detail("my.detail", camelContext.getName());

        if (unhealtyCondition) {
            builder.down();
        } else {
            builder.up();
        }
    }
}

You can now make MyHealthCheck available to Camel by adding an instance to (for example Spring application context) or directly to the Camel Registry.

Loading custom health checks

Camel can discover and load custom health checks from classpath scanning. This requires to annotate the custom health checks with @HealthCheck annotation on the class (see above).

Then the camel-component-maven-plugin can be used to automatic generated service loader file in META-INF/services/org/apache/camel/health-checks that Camel uses to discover the custom health checks.

You must also enable loading custom health check by setting (Camel Main, Camel K, or Camel Quarkus):

camel.main.load-health-checks = true

And in Spring Boot:

camel.springboot.load-health-checks = true

And if you use the classic Spring XML or Blueprint XML, you can enable this on <camelContext> as shown:

<camelContext loadHealthChecks="true">
    ...
</camelContext>

And of course you can also enable loading health checks from Java via CamelContext:

CamelContext context = ...
context.setLoadHealthChecks(true);
The example main-health has a custom health check which is loadable.

Loading custom health checks in Camel Quarkus

If you use Camel Quarkus then you can write custom health checks with MicroProfile Health, which Camel Quarkus can automatically discover during build time compilation and ensure are automatically loaded.

Using Camel’s own health check APIs does however allow building health checks that are usable anywhere you use Camel whether its standalone, spring boot, quarkus, or something else.

Writing custom Health Check for Camel components

You can implement custom health checks in Camel components (currently only for consumers).

To do this, you implement the interface HealthCheckAware on your consumer class, which should return the custom health check in the getter method.

In the custom health check implementation, you can perform the check as shown in the previous section. Camel will then use these custom component health checks when it performs routes health checks.

Examples

There are examples for Camel at:

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