DropwizardMetricsCircuitBreakerListener.java

/*
 * Copyright 2016 LINE Corporation
 *
 * LINE Corporation licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package com.linecorp.armeria.client.circuitbreaker.metrics;

import static java.util.Objects.requireNonNull;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import com.codahale.metrics.MetricRegistry;

import com.linecorp.armeria.client.circuitbreaker.CircuitBreaker;
import com.linecorp.armeria.client.circuitbreaker.CircuitBreakerListener;
import com.linecorp.armeria.client.circuitbreaker.CircuitState;
import com.linecorp.armeria.client.circuitbreaker.EventCount;

/**
 * A {@link CircuitBreakerListener} which monitors the status of {@link CircuitBreaker}s using
 * <a href="https://dropwizard.github.io/metrics/">dropwizard metrics</a>.
 *
 * <p>This class will generate the following metrics.
 *
 * <table summary="metrics that will generated by this class">
 * <tr><th>metric name</th><th>description</th></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.transitions.closed}</td>
 * <td>The number of times that the circuit state has changed to {@code CLOSED}.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.transitions.open}</td>
 * <td>The number of times that the circuit state has changed to {@code OPEN}.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.transitions.halfopen}</td>
 * <td>The number of times that the circuit state has changed to {@code HALF_OPEN}.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.requests.rejected}</td>
 * <td>The number of requests that is rejected by the circuit breaker.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.counter.rate.success}</td>
 * <td>The rate of success requests in the counter time window.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.counter.rate.failure}</td>
 * <td>The rate of failed requests in the counter time window.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.counter.count.success}</td>
 * <td>The count of success requests in the counter time window.</td></tr>
 *
 * <tr><td>{@code {prefix}.{circuit-breaker-name}.counter.count.failure}</td>
 * <td>The count of failed requests in the counter time window.</td></tr>
 *
 * </table>
 */
public final class DropwizardMetricsCircuitBreakerListener implements CircuitBreakerListener {

    private final Map<String, DropwizardCircuitBreakerMetrics> metricsMap = new ConcurrentHashMap<>();

    private final String prefix;

    private final MetricRegistry registry;

    /**
     * Creates a new instance.
     */
    public DropwizardMetricsCircuitBreakerListener(MetricRegistry registry, String prefix) {
        this.registry = requireNonNull(registry, "registry");
        this.prefix = requireNonNull(prefix, "prefix");
    }

    @Override
    public void onStateChanged(CircuitBreaker circuitBreaker, CircuitState state) {
        metricsOf(circuitBreaker).onStateChanged(state);
    }

    @Override
    public void onEventCountUpdated(CircuitBreaker circuitBreaker, EventCount eventCount) {
        metricsOf(circuitBreaker).onCountUpdated(eventCount);
    }

    @Override
    public void onRequestRejected(CircuitBreaker circuitBreaker) {
        metricsOf(circuitBreaker).onRequestRejected();
    }

    private DropwizardCircuitBreakerMetrics metricsOf(CircuitBreaker circuitBreaker) {
        return metricsMap.computeIfAbsent(circuitBreaker.name(),
                                          name -> new DropwizardCircuitBreakerMetrics(prefix, name, registry));
    }
}