com.hotels.styx.client.healthcheck.UrlRequestHealthCheck Maven / Gradle / Ivy

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/**
 * Copyright (C) 2013-2017 Expedia Inc.
 *
 * Licensed 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.hotels.styx.client.healthcheck;

import com.codahale.metrics.Meter;
import com.hotels.styx.api.HttpClient;
import com.hotels.styx.api.HttpRequest;
import com.hotels.styx.api.client.Origin;
import com.hotels.styx.api.metrics.MetricRegistry;
import com.hotels.styx.common.SimpleCache;
import io.netty.buffer.ByteBuf;
import rx.Observer;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.hotels.styx.api.HttpHeaderNames.HOST;
import static com.hotels.styx.api.HttpRequest.Builder.get;
import static com.hotels.styx.client.healthcheck.OriginHealthCheckFunction.OriginState.HEALTHY;
import static com.hotels.styx.client.healthcheck.OriginHealthCheckFunction.OriginState.UNHEALTHY;
import static io.netty.handler.codec.http.HttpResponseStatus.OK;
import static io.netty.util.ReferenceCountUtil.release;

/**
 * Health-check that works by making a request to a URL and ensuring that it gets an HTTP 200 OK code back.
 */
public class UrlRequestHealthCheck implements OriginHealthCheckFunction {
    private static final Observer RELEASE_BUFFER = new DoNothingObserver();

    private final String healthCheckUri;
    private final HttpClient client;
    private final SimpleCache meterCache;

    /**
     * Construct an instance.
     *
     * @param healthCheckUri URI to make health-check requests to
     * @param client         HTTP client to make health-check requests with
     * @param metricRegistry metric registry
     */
    public UrlRequestHealthCheck(String healthCheckUri, HttpClient client, MetricRegistry metricRegistry) {
        this.healthCheckUri = uriWithInitialSlash(healthCheckUri);
        this.client = checkNotNull(client);
        this.meterCache = new SimpleCache<>(origin -> metricRegistry.meter("origins.healthcheck.failure." + origin.applicationId()));
    }

    private static String uriWithInitialSlash(String uri) {
        return uri.startsWith("/") ? uri : "/" + uri;
    }

    @Override
    public void check(Origin origin, OriginHealthCheckFunction.Callback responseCallback) {
        HttpRequest request = newHealthCheckRequestFor(origin);

        client.sendRequest(request).subscribe(response -> {
            if (response.status().equals(OK)) {
                responseCallback.originStateResponse(HEALTHY);
            } else {
                meterCache.get(origin).mark();
                responseCallback.originStateResponse(UNHEALTHY);
            }

            response.body().content().subscribe(RELEASE_BUFFER);
        }, error -> {
            meterCache.get(origin).mark();
            responseCallback.originStateResponse(UNHEALTHY);
        });
    }

    private HttpRequest newHealthCheckRequestFor(Origin origin) {
        return get(healthCheckUri)
                .header(HOST, origin.hostAsString())
                .build();
    }

    // Note: this differs from just calling Observable.subscribe with no arguments, because it ignores errors too, whereas subscribe() throws an exception
    private static class DoNothingObserver implements Observer {
        @Override
        public void onCompleted() {
        }

        @Override
        public void onError(Throwable throwable) {
        }

        @Override
        public void onNext(ByteBuf byteBuf) {
            release(byteBuf);
        }
    }
}