Building

Creating a git release on Github will trigger a build on jitpack: https://jitpack.io/#Financial-Times/advanced-dropwizard-healthcheck

The pom file will NOT be updated and should stay as 'snapshot'.

About

The Advanced Healthcheck library conforms to the FT Health Check Standard.

To use, simply create a health check that extends AdvancedHealthCheck.

E.g.

public class HelloworldHealthCheck extends AdvancedHealthCheck {

    public HelloworldHealthCheck(final String name) {

        super(name);
    }

    @Override
    protected AdvancedResult checkAdvanced() throws Exception {

        if (true) {
            return AdvancedResult.healthy("All is ok");
        }

        return AdvancedResult.error(this, "Not ok");

    }

    @Override
    protected int severity() {
        return 0;
    }

    @Override
    protected String businessImpact() {
        return "business impact";
    }

    @Override
    protected String technicalSummary() {
        return "technical summary";
    }

    @Override
    protected String panicGuideUrl() {
        return "http://mypanicguide.com";
    }

}

Health check id

By default a health check will return its name as its ID. This can be overridden:

    @Override
    protected String id() {
        return "healthcheck-one";
    }

It can then be added to Dropwizard in the standard healthcheck way.

environment.healthChecks().register("my health check", new HelloworldHealthCheck("my health check"));

The AdvancedHealthCheckServlet (by way of the HealthCheckPageData object) provides INFO level logging for Splunk.

event="advancedHealthCheck", action="detail", name="Sign Up App", checkName="Offer API", ok="true", checkOutput="OK"
event="advancedHealthCheck", action="detail", name="Sign Up App", checkName="Cassandra", ok="true", checkOutput="OK"
event="advancedHealthCheck", action="detail", name="Sign Up App", checkName="Subscription API", ok="true", checkOutput="OK"
event="advancedHealthCheck", action="detail", name="Sign Up App", checkName="User API", ok="true", checkOutput="OK"
event="advancedHealthCheck", action="summary", name="Sign Up App", status="OK"

This is configured in your app's YAML configuration file.

loggers:
  #enable advanced health check logging
  "com.ft.platform.dropwizard.HealthCheckPageData": INFO
  #disable advanced health check logging
  "com.ft.platform.dropwizard.HealthCheckPageData": OFF

This will ensure all errors reported through the __health endpoint will be logged. If your monitoring hits another endpoint, such as the built-in Dropwizard endpoint, then wrap your advanced checks in a LoggingAdvancedHealthCheck.

Bundle

The advanced health check page can be added to your app using a convenient bundle.

Configuration of the AdvancedHealthCheck class is done via the Dropwizard config file. For example:

appInfo:
  systemCode: test-system-code
  description: "tests description"
  runbookUrl: "http://test-runbook/url"

To support this, your application's configuration class needs to implement the following interface:

src/main/java/com/ft/platform/dropwizard/ConfigWithAppInfo.java

Example:

public class AppConfig extends Configuration implements ConfigWithAppInfo {
    @JsonProperty
    private AppInfo appInfo;
    @Override
    public AppInfo getAppInfo() { return appInfo; }
}

GTG

"Good to go" is also supported as an additional bundle. Your dropwizard config will need to implement the ConfigWithGtg interface:

public static class MyConfig extends Configuration implements ConfigWithGTG{    
    @JsonProperty
    private GTGConfig gtg = new GTGConfig();

Add the bundle:

@Override
public void initialize(final Bootstrap bootstrap) {
    bootstrap.addBundle(new GoodToGoConfiguredBundle(new DefaultGoodToGoChecker()));
}

This example will result in a /__gtg endpoint that is based on the health check results. One or more errors imply not good to go.

If needed, you can supply your own GoodToGoChecker implementation instead of using DefaultGoodToGoChecker.

Async Health Checks

WARNING: this feature should be considered experimental!

This library also provides an asynchronous version of the advanced health check. These health checks are run on a schedule, instead of being triggered by requests to the __health endpoint; this ensures a timely response to the endpoint, returning the result of the most recently run health check:

To register the AdvancedAsyncHealthCheckBundle bundle, your Dropwizard app config class will need to implement the AdvancedHealthCheckConfig interface in order to configure the scheduling of the health check runs.

Settings, in addition to AppInfo (described above), defined in the AsyncScheduleConfig class are:

• The initial delay period before health checks start to run (this may be useful if your server startup takes a long time).
• The period to wait after one health check finishes before a new one should be started.
• The TimeUnit to use for the other 2 fields.

Health check failure Graphite stats

If you are using the Metrics library, this bundle will increment a counter whenever a health check fails, allowing you to collect statistics on the health checks that fail most often, which may help you to prioritise the order of health checks that you focus on fixing.

To start reporting metrics to Graphite, take a look at Reporting to Graphite.

NB. The metrics will appear in Graphite in a folder (under your chosen application prefix) called healthcheck-failures.<name of health check>, with some special characters (such as / and .) converted into underscores. For example, a user-cred-svc health check failure count for a health check called "Kafka health check for http://cmdb.ft.com/systems/usr-cred-svc" will exist under the following path in Graphite:

/membership/aim/user-credentials-service/local/local/web/local/healthcheck-failures/Kafka-healthcheck-for-http:__cmdb_ft_com_