org.apache.aurora.scheduler.http.LeaderHealth.java Source code

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Here is the source code for org.apache.aurora.scheduler.http.LeaderHealth.java

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/**
 * 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 org.apache.aurora.scheduler.http;

import java.util.Map;
import java.util.Objects;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;

import org.apache.aurora.common.collections.Pair;

import static javax.servlet.http.HttpServletResponse.SC_BAD_GATEWAY;
import static javax.servlet.http.HttpServletResponse.SC_OK;
import static javax.servlet.http.HttpServletResponse.SC_SERVICE_UNAVAILABLE;

import static org.apache.aurora.scheduler.http.LeaderRedirect.LeaderStatus;
import static org.apache.aurora.scheduler.http.LeaderRedirect.LeaderStatus.LEADING;
import static org.apache.aurora.scheduler.http.LeaderRedirect.LeaderStatus.NOT_LEADING;
import static org.apache.aurora.scheduler.http.LeaderRedirect.LeaderStatus.NO_LEADER;

/**
 * Servlet that exposes the leader health. It is meant to be used by load balancers such as
 * ELB to always forward to the leading scheduler.
 */
@Path("/leaderhealth")
public class LeaderHealth {

    private static final Map<LeaderStatus, Pair<Integer, String>> RESPONSE_CODES = ImmutableMap.of(LEADING,
            Pair.of(SC_OK, "This is the leading scheduler."), NOT_LEADING,
            Pair.of(SC_SERVICE_UNAVAILABLE, "Another instance is the leading scheduler."), NO_LEADER,
            Pair.of(SC_BAD_GATEWAY, "There is no leading scheduler or the leader is unknown."));

    private static final String HELP = generateHelpText();

    private final LeaderRedirect leaderRedirect;

    @Inject
    LeaderHealth(LeaderRedirect leaderRedirect) {
        this.leaderRedirect = Objects.requireNonNull(leaderRedirect);
    }

    @VisibleForTesting
    static String getHelpText(LeaderStatus status) {
        return "Current status: " + RESPONSE_CODES.get(status).getSecond() + "\n\n" + HELP;
    }

    /**
     * Gets the leadership status of the scheduler.
     *
     * @return HTTP response.
     */
    @GET
    public Response get() {
        LeaderStatus leaderStatus = leaderRedirect.getLeaderStatus();
        return Response.status(RESPONSE_CODES.get(leaderStatus).getFirst()).type(MediaType.TEXT_PLAIN_TYPE)
                .entity(getHelpText(leaderStatus)).build();
    }

    private static String generateHelpText() {
        Map<Integer, String> details = Maps
                .transformValues(Maps.uniqueIndex(RESPONSE_CODES.values(), Pair::getFirst), Pair::getSecond);

        return "This endpoint can indicate to a load balancer which among a group of schedulers "
                + "is leading.\n\nThe response codes are:\n"
                + Joiner.on("\n").withKeyValueSeparator(": ").join(details);
    }
}