Simple Dropwizard HealthCheck for a Neo4j server

Neo4jHealthCheck.java

import com.codahale.metrics.health.HealthCheck;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.jaxrs.json.JacksonJsonProvider;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.config.ClientConfig;
import com.sun.jersey.api.client.config.DefaultClientConfig;
import javax.ws.rs.core.MediaType;

public class Neo4jHealthCheck extends HealthCheck {

    private final String serviceRoot = "/db/data/";
    private String expectedVersion = null;
    private final String urlString;

    private final Client client;

    public Neo4jHealthCheck(Client client, String host, int port) {
        StringBuilder urlStringBuilder = new StringBuilder();
        urlStringBuilder.append("http://");
        urlStringBuilder.append(host);
        urlStringBuilder.append(":");
        urlStringBuilder.append(port);
        urlStringBuilder.append(serviceRoot);

        this.client = client;

        urlString = urlStringBuilder.toString();
    }

    public Neo4jHealthCheck(Client client, String host, int port, String expectedVersion) {
        this(client, host, port);
        this.expectedVersion = expectedVersion;
    }

    @Override
    protected Result check() throws Exception {
        
        RootResponse response = client.resource(urlString).accept(MediaType.APPLICATION_JSON).get(RootResponse.class);

        if (response == null) {
            return Result.unhealthy("Null response from Neo4j at " + urlString);
        }

        if (expectedVersion != null) {
            if (!expectedVersion.equals(response.neo4jVersion)) {
                return Result.unhealthy("Expected Neo4j version " + expectedVersion + " but found " + response.neo4jVersion);
            }
        }
        return Result.healthy();
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    private static class RootResponse {
        @JsonProperty("neo4j_version")
        private String neo4jVersion;
    }
}

For anyone using Dropwizard in conjunction with the REST-based interface of a Neo4j graph database server, this is a simple HealthCheck implementation.

If you're running Neo4j as an HA cluster, you'll probably want to modify the endpoints to test as described in the HA documentation.

To create the Jersey Client instance to pass in to the constructor, you will want to add dropwizard-client to your project and configure as described.

The end result might look like

  final Client jerseyClient = new JerseyClientBuilder(environment).using(config.getJerseyClientConfiguration()).build(getName());
  environment.healthChecks().register("neo4j", new Neo4jHealthCheck(jerseyClient, config.getNeo4j().getHostName(), config.getNeo4j().getPort(), "2.2.1"));