---

title: “HealthCheck” lang: en ref: healthcheck permalink: /docs/users/healthcheck/ excerpt: “HealthCheck” last_modified_at: 2017-12-30T10:01:43-04:00 redirect_from:

• /theme-setup/

---

{% include toc %} Java Chassis had support HealthCheck since 1.0.0-m1.

Introduction

Microservice always depend on many middlewares like database, message queue etc. Also depend on other microservices. When microservice is unavailable, may caused by database, we need record details into log file or show details on dashboard: database disk had full? database accress right had invalid? or database accress user and password had changed? not only a DOWN state, details can help dev ops find where is the problem and solve it faster.

HealthCheck provide an extensible mechanism, user can create custom check point in order to probe whether the core dependencies are available, if any one is unavailable, report the details:

How to use

Implement custom HealthCheck

It is easy to implement Java Chassis HealthCheck, implements from org.apache.servicecomb.foundation.metrics.health.HealthChecker interface and override these methods:

Method Name	Description
getName	Return the name of HealthChecker, please make sure do not duplicated, otherwise the results of same name will merged
check	Concrete implementation of Check logic

Example:

public class MySqlHealthChecker implements HealthChecker {
  @Override
  public String getName() {
    return "mysql";
  }

  @Override
  public HealthCheckResult check() {
    //add your health check code here
    Connection connection = null;
    try {
      connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test_db?useSSL=false", "root", "pwd");
      return new HealthCheckResult(true, "local mysql health check", "");
    } catch (SQLException e) {
      LOG.error("Cannot connect the localhost mysql. ", e);
      return new HealthCheckResult(false, "local mysql health check", e.toString());
    } finally {
      if (connection != null) {
        try {
          connection.close();
        } catch (SQLException e) {
          LOG.error("Close connect the localhost mysql error. ", e);
        }
      }
    }
  }
}

We use SPI to load it, create an new file named org.apache.servicecomb.foundation.metrics.health.HealthChecker under esource/META-INF/services folder, write class name of your HealthChecker into it, like:

org.apache.servicecomb.samples.metrics.extendhealthcheck.MySqlHealthChecker

Verify HealthCheck

After microservice startup, HealthCheck will publish use Rest endpoint, the publish address is same as servicecomb.rest.address, if had configure in microservice.yaml like:

servicecomb:
  rest:
    address: 0.0.0.0:8080

We can get HealthCheck final result by accress http://localhost:8080/health , also can get detail results by accress http://localhost:8080/health/detail .

NOTE:

1. The implementation of Rest publish is in metrics-core, so need import this dependency;
2. The result of /health is the final result of all HealthCheckers, true or false, if healthy result of any HealthChecker return false, then this value will false.

Other Reference

We had provided a sample at samples/metrics-extend-healthcheck.