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 three standard 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 startup the first time, and are retried to be started in the background with backoff delays.

  • 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.

Readiness and Liveness

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

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

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

Health Check configuration

The HealthCheckConfiguration has the following options:

Name Default Description

enabled

true

Set if the check associated to this configuration is enabled or not.

interval

Set the check interval in milli seconds.

failureThreshold

Set the number of failure before reporting the service as un-healthy.

The interval and failureThreshold are used for configuring health checks to deal with flaky checks. For example assume you do not want to regard a check as immediately DOWN when a check for the first time returns a response as DOWN. So you can specify the interval=10000 and failureThreshold=5, which means that the check has slacks, and will only report it as DOWN when there has been 5 failures in a row, with a minimum of 10 second of interval between these checks. So in other words after minimum 50 seconds and 5 calls then it can be reported as DOWN.

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 automatic enable context, routes and registry health-checks if camel-health is detected on the classpath. They are all enabled by default. However you can configure them, for example to turn it 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.contextEnabled=true
camel.health.routesEnabled=false
camel.health.registryEnabled=false

Configuring routes health-check

The routes health check supports filtering by route id, or endpoint uri using a pattern style (* as wildcard, and regexp supported). For example to turn off all routes that are from kafka, you can do:

Notice the syntax is a map [] where the key is the route id pattern. Its important to set the parent option to refer to what health-check this configuration applies for such as routes or registry. 
camel.health.config[kafka*].parent=routes
camel.health.config[kafka*].enabled=false

It’s possible to set a default fallback configuration using [*] as the route id:

camel.health.config[kafka*].parent=routes
camel.health.config[kafka*].enabled=false
camel.health.config[*].parent=routes
camel.health.config[*].enabled=true
camel.health.config[*].failure-threshold=10

JMX management

The health check is managable 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).

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 unwanated checkes, 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:

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.

The example camel-example-main-health has a custom health check.

Examples

There are examples for Camel at:

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