backends-common/opensearch/src/main/java/org/apache/james/backends/opensearch/ElasticSearchHealthCheck.java

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package org.apache.james.backends.opensearch;

import java.io.IOException;
import java.util.Set;

import javax.inject.Inject;

import org.apache.commons.lang3.NotImplementedException;
import org.apache.james.core.healthcheck.ComponentName;
import org.apache.james.core.healthcheck.HealthCheck;
import org.apache.james.core.healthcheck.Result;
import org.opensearch.action.admin.cluster.health.ClusterHealthRequest;
import org.opensearch.action.admin.cluster.health.ClusterHealthResponse;
import org.opensearch.client.Requests;

import com.google.common.annotations.VisibleForTesting;

import reactor.core.publisher.Mono;

public class ElasticSearchHealthCheck implements HealthCheck {
    private static final ComponentName COMPONENT_NAME = new ComponentName("ElasticSearch Backend");

    private final Set<IndexName> indexNames;
    private final ReactorElasticSearchClient client;

    @Inject
    ElasticSearchHealthCheck(ReactorElasticSearchClient client, Set<IndexName> indexNames) {
        this.client = client;
        this.indexNames = indexNames;
    }

    @Override
    public ComponentName componentName() {
        return COMPONENT_NAME;
    }

    @Override
    public Mono<Result> check() {
        String[] indices = indexNames.stream()
            .map(IndexName::getValue)
            .toArray(String[]::new);
        ClusterHealthRequest request = Requests.clusterHealthRequest(indices);

        return client.health(request)
            .map(this::toHealthCheckResult)
            .onErrorResume(IOException.class, e -> Mono.just(
                Result.unhealthy(COMPONENT_NAME, "Error while contacting cluster", e)));
    }

    @VisibleForTesting
    Result toHealthCheckResult(ClusterHealthResponse response) {
        switch (response.getStatus()) {
            case GREEN:
            case YELLOW:
                return Result.healthy(COMPONENT_NAME);
            case RED:
                return Result.unhealthy(COMPONENT_NAME, response.getClusterName() + " status is RED");
            default:
                throw new NotImplementedException("Un-handled ElasticSearch cluster status");
        }
    }
}