storm-server/src/test/java/org/apache/storm/scheduler/resource/strategies/scheduling/TestLargeCluster.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.storm.scheduler.resource.strategies.scheduling;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.storm.Config;
import org.apache.storm.DaemonConfig;
import org.apache.storm.generated.StormTopology;
import org.apache.storm.metric.StormMetricsRegistry;
import org.apache.storm.scheduler.Cluster;
import org.apache.storm.scheduler.ExecutorDetails;
import org.apache.storm.scheduler.INimbus;
import org.apache.storm.scheduler.IScheduler;
import org.apache.storm.scheduler.SupervisorDetails;
import org.apache.storm.scheduler.Topologies;
import org.apache.storm.scheduler.TopologyDetails;
import org.apache.storm.scheduler.WorkerSlot;
import org.apache.storm.scheduler.resource.ResourceAwareScheduler;
import org.apache.storm.scheduler.resource.TestUtilsForResourceAwareScheduler;
import org.apache.storm.scheduler.resource.normalization.NormalizedResources;
import org.apache.storm.scheduler.resource.normalization.NormalizedResourcesExtension;
import org.apache.storm.scheduler.resource.normalization.ResourceMetrics;
import org.apache.storm.utils.Time;
import org.apache.storm.utils.Utils;
import org.junit.Assert;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.concurrent.atomic.AtomicInteger;

@ExtendWith({NormalizedResourcesExtension.class})
public class TestLargeCluster {
    private static final Logger LOG = LoggerFactory.getLogger(TestLargeCluster.class);

    public static final String TEST_CLUSTER_01 = "largeCluster01";
    public static final String TEST_CLUSTER_02 = "largeCluster02";

    public static final String TEST_CLUSTER_NAME = TEST_CLUSTER_02;
    public static final String TEST_RESOURCE_PATH = "clusterconf/" + TEST_CLUSTER_NAME;
    public static final String COMPRESSED_SERIALIZED_TOPOLOGY_FILENAME_ENDING = "code.ser";
    public static final String COMPRESSED_SERIALIZED_CONFIG_FILENAME_ENDING = "conf.ser";

    private static IScheduler scheduler = null;

    @AfterEach
    public void cleanup() {
        if (scheduler != null) {
            scheduler.cleanup();
            scheduler = null;
        }
    }

    /**
     * Get the list of serialized topology (*code.ser) and configuration (*conf.ser)
     * resource files in the path. The resources are sorted so that paired topology and conf
     * files are sequential. Unpaired files may be ignored by the caller.
     *
     * @param path directory in which resources exist.
     * @return
     * @throws IOException
     */
    public static List<String> getResourceFiles(String path) throws IOException {
        List<String> fileNames = new ArrayList<>();

        try (
                InputStream in = getResourceAsStream(path);
                BufferedReader br = new BufferedReader(new InputStreamReader(in))
        ) {
            String resource;

            while ((resource = br.readLine()) != null) {
                if (resource.endsWith(COMPRESSED_SERIALIZED_TOPOLOGY_FILENAME_ENDING)
                        || resource.endsWith(COMPRESSED_SERIALIZED_CONFIG_FILENAME_ENDING)) {
                    fileNames.add(path + "/" + resource);
                }
            }
            Collections.sort(fileNames);
        }
        return fileNames;
    }

    /**
     * InputStream to read the fully qualified resource path.
     *
     * @param resource
     * @return
     */
    public static InputStream getResourceAsStream(String resource) {
        final InputStream in = getContextClassLoader().getResourceAsStream(resource);
        return in == null ? ClassLoader.getSystemClassLoader().getResourceAsStream(resource) : in;
    }

    /**
     * Read the contents of the fully qualified resource path.
     *
     * @param resource
     * @return
     * @throws Exception
     */
    public static byte[] getResourceAsBytes(String resource) throws Exception {
        InputStream in = getResourceAsStream(resource);
        if (in == null) {
            return null;
        }
        try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
            while (in.available() > 0) {
                out.write(in.read());
            }
            return out.toByteArray();
        }
    }

    public static ClassLoader getContextClassLoader() {
        return Thread.currentThread().getContextClassLoader();
    }

    /**
     * Create an array of TopologyDetails by reading serialized files for topology and configuration in the
     * resource path. Skip topologies with no executors/components.
     *
     * @param failOnParseError throw exception if there are unmatched files, otherwise ignore unmatched and read errors.
     * @return An array of TopologyDetails representing resource files.
     * @throws Exception
     */
    public static TopologyDetails[] createTopoDetailsArray(boolean failOnParseError) throws Exception {
        List<TopologyDetails> topoDetailsList = new ArrayList<>();
        List<String> errors = new ArrayList<>();
        List<String> resources = getResourceFiles(TEST_RESOURCE_PATH);
        Map<String, String> codeResourceMap = new TreeMap<>();
        Map<String, String> confResourceMap = new HashMap<>();
        for (int i = 0 ; i < resources.size() ; i++) {
            String resource = resources.get(i);
            int idxOfSlash = resource.lastIndexOf("/");
            int idxOfDash = resource.lastIndexOf("-");
            String nm = idxOfDash > idxOfSlash
                    ? resource.substring(idxOfSlash + 1, idxOfDash)
                    : resource.substring(idxOfSlash + 1, resource.length() - COMPRESSED_SERIALIZED_TOPOLOGY_FILENAME_ENDING.length());
            if (resource.endsWith(COMPRESSED_SERIALIZED_TOPOLOGY_FILENAME_ENDING)) {
                codeResourceMap.put(nm, resource);
            } else if (resource.endsWith(COMPRESSED_SERIALIZED_CONFIG_FILENAME_ENDING)) {
                confResourceMap.put(nm, resource);
            } else {
                LOG.info("Ignoring unsupported resource file " + resource);
            }
        }
        String[] examinedConfParams = {
                Config.TOPOLOGY_NAME,
                Config.TOPOLOGY_SCHEDULER_STRATEGY,
                Config.TOPOLOGY_PRIORITY,
                Config.TOPOLOGY_WORKERS,
                Config.TOPOLOGY_WORKER_MAX_HEAP_SIZE_MB,
                Config.TOPOLOGY_SUBMITTER_USER,
                Config.TOPOLOGY_ACKER_CPU_PCORE_PERCENT,
                Config.TOPOLOGY_ACKER_RESOURCES_OFFHEAP_MEMORY_MB,
                Config.TOPOLOGY_ACKER_RESOURCES_ONHEAP_MEMORY_MB,
        };

        for (String nm : codeResourceMap.keySet()) {
            String codeResource = codeResourceMap.get(nm);
            if (!confResourceMap.containsKey(nm)) {
                String err = String.format("Ignoring topology file %s because of missing config file for %s", codeResource, nm);
                errors.add(err);
                LOG.error(err);
                continue;
            }
            String confResource = confResourceMap.get(nm);
            LOG.info("Found matching topology and config files: {}, {}", codeResource, confResource);
            StormTopology stormTopology;
            try {
                stormTopology = Utils.deserialize(getResourceAsBytes(codeResource), StormTopology.class);
            } catch (Exception ex) {
                String err = String.format("Cannot read topology from resource %s", codeResource);
                errors.add(err);
                LOG.error(err, ex);
                continue;
            }

            Map<String, Object> conf;
            try {
                conf = Utils.fromCompressedJsonConf(getResourceAsBytes(confResource));
            } catch (RuntimeException | IOException ex) {
                String err = String.format("Cannot read configuration from resource %s", confResource);
                errors.add(err);
                LOG.error(err, ex);
                continue;
            }
            // fix 0.10 conf class names
            String[] configParamsToFix = {Config.TOPOLOGY_SCHEDULER_STRATEGY, Config.STORM_NETWORK_TOPOGRAPHY_PLUGIN,
                    DaemonConfig.RESOURCE_AWARE_SCHEDULER_PRIORITY_STRATEGY };
            for (String configParam: configParamsToFix) {
                if (!conf.containsKey(configParam)) {
                    continue;
                }
                String className = (String) conf.get(configParam);
                if (className.startsWith("backtype")) {
                    className = className.replace("backtype", "org.apache");
                    conf.put(configParam, className);
                }
            }
            // fix conf params used by ConstraintSolverStrategy
            if (!conf.containsKey(DaemonConfig.RESOURCE_AWARE_SCHEDULER_MAX_STATE_SEARCH)) {
                conf.put(DaemonConfig.RESOURCE_AWARE_SCHEDULER_MAX_STATE_SEARCH, 10_000);
            }
            if (!conf.containsKey(Config.TOPOLOGY_RAS_CONSTRAINT_MAX_STATE_SEARCH)) {
                conf.put(Config.TOPOLOGY_RAS_CONSTRAINT_MAX_STATE_SEARCH, 10_000);
            }
            if (!conf.containsKey(Config.TOPOLOGY_RAS_ACKER_EXECUTORS_PER_WORKER)) {
                conf.put(Config.TOPOLOGY_RAS_ACKER_EXECUTORS_PER_WORKER, 1);
            }

            String topoId = nm;
            String topoName = (String) conf.getOrDefault(Config.TOPOLOGY_NAME, nm);

            // conf
            StringBuffer sb = new StringBuffer("Config for " + nm + ": ");
            for (String param : examinedConfParams) {
                Object val = conf.getOrDefault(param, "<null>");
                sb.append(param).append("=").append(val).append(", ");
            }
            LOG.info(sb.toString());

            // topo
            Map<ExecutorDetails, String> execToComp = TestUtilsForResourceAwareScheduler.genExecsAndComps(stormTopology);
            LOG.info("Topology \"{}\" spouts={}, bolts={}, execToComp size is {}", topoName,
                    stormTopology.get_spouts_size(), stormTopology.get_bolts_size(), execToComp.size());
            if (execToComp.isEmpty()) {
                LOG.error("Topology \"{}\" Ignoring BAD topology with zero executors", topoName);
                continue;
            }
            int numWorkers = Integer.parseInt("" + conf.getOrDefault(Config.TOPOLOGY_WORKERS, "0"));
            TopologyDetails topo = new TopologyDetails(topoId, conf, stormTopology,  numWorkers,
                    execToComp, Time.currentTimeSecs(), "user");
            topo.getUserTopolgyComponents(); // sanity check - normally this should not fail

            topoDetailsList.add(topo);
        }
        if (!errors.isEmpty() && failOnParseError) {
            throw new Exception("Unable to parse all serialized objects\n\t" + String.join("\n\t", errors));
        }
        return topoDetailsList.toArray(new TopologyDetails[0]);
    }

    /**
     * Check if the files in the resource directory are matched, can be read properly, and code/config files occur
     * in matched pairs.
     *
     * @throws Exception showing bad and unmatched resource files.
     */
    @Test
    public void testReadSerializedTopologiesAndConfigs() throws Exception {
        List<String> resources = getResourceFiles(TEST_RESOURCE_PATH);
        Assert.assertTrue("No resource files found in " + TEST_RESOURCE_PATH, !resources.isEmpty());
        TopologyDetails[] topoDetailsArray = createTopoDetailsArray(true);
    }

    /**
     * Create one supervisor and add to the supervisors list.
     *
     * @param rack rack-number
     * @param superInRack supervisor number in the rack
     * @param cpu percentage
     * @param mem in megabytes
     * @param numPorts number of ports on this supervisor
     * @param sups returned map os supervisors
     */
    private static void createAndAddOneSupervisor(
            int rack, int superInRack, double cpu, double mem, int numPorts,
            Map<String, SupervisorDetails> sups) {

        List<Number> ports = new LinkedList<>();
        for (int p = 0; p < numPorts; p++) {
            ports.add(p);
        }
        String superId = String.format("r%03ds%03d", rack, superInRack);
        String hostId  = String.format("host-%03d-rack-%03d", superInRack, rack);
        Map<String, Double> resourceMap = new HashMap<>();
        resourceMap.put(Config.SUPERVISOR_CPU_CAPACITY, cpu);
        resourceMap.put(Config.SUPERVISOR_MEMORY_CAPACITY_MB, mem);
        resourceMap.put("network.resource.units", 50.0);
        SupervisorDetails sup = new SupervisorDetails(superId,
                hostId, null, ports,
                NormalizedResources.RESOURCE_NAME_NORMALIZER.normalizedResourceMap(resourceMap));
        sups.put(sup.getId(), sup);
    }

    /**
     * Create supervisors for a larger cluster configuration.
     *
     * @param reducedSupervisorsPerRack number of supervisors to reduce in rack.
     * @return created supervisors.
     */
    private static Map<String, SupervisorDetails> createSupervisors(int reducedSupervisorsPerRack) {
        if (TEST_CLUSTER_NAME.equals(TEST_CLUSTER_02)) {
            return createSupervisorsForCluster02(reducedSupervisorsPerRack);
        } else {
            return createSupervisorsForCluster01(reducedSupervisorsPerRack);
        }
    }

    /**
     * Create supervisors for a newer {@link #TEST_CLUSTER_02} cluster configuration to mimic a large cluster in use.
     *
     * @param reducedSupervisorsPerRack number of supervisors to reduce per rack.
     * @return created supervisors.
     */
    private static Map<String, SupervisorDetails> createSupervisorsForCluster02(int reducedSupervisorsPerRack) {
        Collection<SupervisorDistribution> supervisorDistributions = SupervisorDistribution.getSupervisorDistribution02();
        Map<String, Collection<SupervisorDistribution>> byRackId = SupervisorDistribution.mapByRackId(supervisorDistributions);
        LOG.info("Cluster={}, Designed capacity: {}", TEST_CLUSTER_NAME, SupervisorDistribution.clusterCapacity(supervisorDistributions));

        Map<String, SupervisorDetails> retList = new HashMap<>();
        Map<String, AtomicInteger> seenRacks = new HashMap<>();
        byRackId.forEach((rackId, list) -> {
            int tmpRackSupervisorCnt = list.stream().mapToInt(x -> x.supervisorCnt).sum() - Math.abs(reducedSupervisorsPerRack);
            if (tmpRackSupervisorCnt > Math.abs(reducedSupervisorsPerRack)) {
                tmpRackSupervisorCnt -= Math.abs(reducedSupervisorsPerRack);
            }
            final int adjustedRackSupervisorCnt = tmpRackSupervisorCnt;
            list.forEach(x -> {
                int supervisorCnt = x.supervisorCnt;
                for (int i = 0; i < supervisorCnt ; i++) {
                    int superInRack = seenRacks.computeIfAbsent(rackId, z -> new AtomicInteger(-1)).incrementAndGet();
                    int rackNum = seenRacks.size() - 1;
                    if (superInRack >= adjustedRackSupervisorCnt) {
                        continue;
                    }
                    createAndAddOneSupervisor(rackNum, superInRack, x.cpuPercent, x.memoryMb, x.slotCnt, retList);
                }
            });
        });
        return retList;
    }

    /**
     * Create supervisors for a non-uniform supervisor distribution closely (but not exactly) mimics a large cluster in use.
     *
     * @param reducedSupervisorsPerRack is the reduction in supervisors per rack to constrain capacity (15 is tight)
     * @return supervisor details indexed by id
     */
    private static Map<String, SupervisorDetails> createSupervisorsForCluster01(int reducedSupervisorsPerRack) {
        int numSupersPerRack = 82 - Math.abs(reducedSupervisorsPerRack);
        int numPorts = 50;

        Map<String, SupervisorDetails> retList = new HashMap<>();

        for (int rack = 0 ; rack < 12 ; rack++) {
            double cpu = 3600; // %percent
            double mem = 178_000; // MB
            for (int superInRack = 0; superInRack < numSupersPerRack ; superInRack++) {
                createAndAddOneSupervisor(rack, superInRack, cpu - 100 * (superInRack % 2), mem, numPorts, retList);
            }
        }
        for (int rack = 12 ; rack < 14 ; rack++) {
            double cpu = 2400; // %percent
            double mem = 118_100; // MB
            for (int superInRack = 0; superInRack < numSupersPerRack ; superInRack++) {
                createAndAddOneSupervisor(rack, superInRack, cpu - 100 * (superInRack % 2), mem, numPorts, retList);
            }
        }
        for (int rack = 14 ; rack < 16 ; rack++) {
            double cpu = 1200; // %percent
            double mem = 42_480; // MB
            for (int superInRack = 0; superInRack < numSupersPerRack ; superInRack++) {
                createAndAddOneSupervisor(rack, superInRack, cpu - 100 * (superInRack % 2), mem, numPorts, retList);
            }
        }
        return retList;
    }

    /**
     * Create a large cluster, read topologies and configuration from resource directory and schedule.
     *
     * @throws Exception
     */
    @Test
    public void testLargeCluster() throws Exception {
        Map<String, SupervisorDetails> supervisors = createSupervisors(0);

        TopologyDetails[] topoDetailsArray = createTopoDetailsArray(false);
        Assert.assertTrue("No topologies found", topoDetailsArray.length > 0);
        Topologies topologies = new Topologies(topoDetailsArray);

        Config confWithDefaultStrategy = new Config();
        confWithDefaultStrategy.putAll(topoDetailsArray[0].getConf());
        confWithDefaultStrategy.put(Config.TOPOLOGY_SCHEDULER_STRATEGY, DefaultResourceAwareStrategy.class.getName());
        confWithDefaultStrategy.put(
                Config.STORM_NETWORK_TOPOGRAPHY_PLUGIN,
                TestUtilsForResourceAwareScheduler.GenSupervisorsDnsToSwitchMapping.class.getName());

        INimbus iNimbus = new INimbusTest();
        Cluster cluster = new Cluster(iNimbus, new ResourceMetrics(new StormMetricsRegistry()), supervisors, new HashMap<>(),
                topologies, confWithDefaultStrategy);

        scheduler = new ResourceAwareScheduler();

        List<Class> classesToDebug = Arrays.asList(DefaultResourceAwareStrategy.class,
                GenericResourceAwareStrategy.class, ResourceAwareScheduler.class,
                Cluster.class
        );
        Level logLevel = Level.INFO ; // switch to Level.DEBUG for verbose otherwise Level.INFO
        classesToDebug.forEach(x -> Configurator.setLevel(x.getName(), logLevel));
        long startTime = System.currentTimeMillis();
        scheduler.prepare(confWithDefaultStrategy, new StormMetricsRegistry());
        scheduler.schedule(topologies, cluster);
        long endTime = System.currentTimeMillis();
        LOG.info("Scheduling Time: {} topologies in {} seconds", topoDetailsArray.length, (endTime - startTime) / 1000.0);

        for (TopologyDetails td : topoDetailsArray) {
            TestUtilsForResourceAwareScheduler.assertTopologiesFullyScheduled(cluster, td.getName());
        }

        // Remove topology and reschedule it
        for (int i = 0 ; i < topoDetailsArray.length ; i++) {
            startTime = System.currentTimeMillis();
            TopologyDetails topoDetails = topoDetailsArray[i];
            cluster.unassign(topoDetails.getId());
            LOG.info("({}) Removed topology {}", i, topoDetails.getName());
            IScheduler rescheduler = new ResourceAwareScheduler();
            rescheduler.prepare(confWithDefaultStrategy, new StormMetricsRegistry());
            rescheduler.schedule(topologies, cluster);
            TestUtilsForResourceAwareScheduler.assertTopologiesFullyScheduled(cluster, topoDetails.getName());
            endTime = System.currentTimeMillis();
            LOG.info("({}) Scheduling Time: Removed topology {} and rescheduled in {} seconds", i, topoDetails.getName(), (endTime - startTime) / 1000.0);
        }
        classesToDebug.forEach(x -> Configurator.setLevel(x.getName(), Level.INFO));
    }

    public static class SupervisorDistribution {
        final String rackId;
        final int supervisorCnt;
        final int slotCnt;
        final int memoryMb;
        final int cpuPercent;

        public SupervisorDistribution(int supervisorCnt, String rackId, int slotCnt, int memoryMb, int cpuPercent) {
            this.rackId = rackId;
            this.supervisorCnt = supervisorCnt;
            this.slotCnt = slotCnt;
            this.memoryMb = memoryMb;
            this.cpuPercent = cpuPercent;
        }

        public static Map<String, Collection<SupervisorDistribution>> mapByRackId(Collection<SupervisorDistribution> supervisors) {
            Map<String, Collection<SupervisorDistribution>> retVal = new HashMap<>();
            supervisors.forEach(x -> retVal.computeIfAbsent(x.rackId, rackId -> new ArrayList<>()).add(x));
            return retVal;
        }

        public static Collection<SupervisorDistribution> getSupervisorDistribution02() {
            return Arrays.asList(
                // Cnt, Rack,    Slot, Mem, CPU
                new SupervisorDistribution(78, "r001", 12, 42461, 1100),
                new SupervisorDistribution(146, "r002", 36, 181362, 3500),
                new SupervisorDistribution(18, "r003", 36, 181362, 3500),
                new SupervisorDistribution(120, "r004", 36, 181362, 3500),
                new SupervisorDistribution(24, "r005", 36, 181362, 3500),
                new SupervisorDistribution(16, "r005", 48, 177748, 4700),
                new SupervisorDistribution(12, "r006", 18, 88305, 1800),
                new SupervisorDistribution(368, "r006", 36, 181205, 3500),
                new SupervisorDistribution(62, "r007", 48, 177748, 4700),
                new SupervisorDistribution(50, "r008", 36, 181348, 3500),
                new SupervisorDistribution(64, "r008", 48, 177748, 4700),
                new SupervisorDistribution(74, "r009", 48, 177748, 4700),
                new SupervisorDistribution(74, "r010", 48, 177748, 4700),
                new SupervisorDistribution(10, "r011", 48, 177748, 4700),
                new SupervisorDistribution(78, "r012", 24, 120688, 2300),
                new SupervisorDistribution(150, "r013", 48, 177748, 4700),
                new SupervisorDistribution(76, "r014", 36, 181362, 3500),
                new SupervisorDistribution(38, "r015", 48, 174431, 4700),
                new SupervisorDistribution(78, "r016", 36, 181375, 3500),
                new SupervisorDistribution(72, "r017", 36, 181362, 3500),
                new SupervisorDistribution(80, "r018", 36, 181362, 3500),
                new SupervisorDistribution(76, "r019", 36, 181362, 3500),
                new SupervisorDistribution(78, "r020", 24, 120696, 2300),
                new SupervisorDistribution(80, "r021", 24, 120696, 2300)
            );
        }

        public static String clusterCapacity(Collection<SupervisorDistribution> supervisorDistributions) {
            long cpuPercent = 0;
            long memoryMb = 0;
            int supervisorCnt = 0;
            Set<String> racks = new HashSet<>();

            for (SupervisorDistribution x: supervisorDistributions) {
                memoryMb += (x.supervisorCnt * x.memoryMb);
                cpuPercent += (x.supervisorCnt * x.cpuPercent);
                supervisorCnt += x.supervisorCnt;
                racks.add(x.rackId);
            };
            return String.format("Cluster summary: Racks=%d, Supervisors=%d, memoryMb=%d, cpuPercent=%d",
                racks.size(), supervisorCnt, memoryMb, cpuPercent);
        }
    }

    public static class INimbusTest implements INimbus {
        @Override
        public void prepare(Map<String, Object> topoConf, String schedulerLocalDir) {

        }

        @Override
        public Collection<WorkerSlot> allSlotsAvailableForScheduling(Collection<SupervisorDetails> existingSupervisors,
                                                                     Topologies topologies, Set<String> topologiesMissingAssignments) {
            //return null;
            Set<WorkerSlot> ret = new HashSet<>();
            for (SupervisorDetails sd : existingSupervisors) {
                String id = sd.getId();
                for (Number port : (Collection<Number>) sd.getMeta()) {
                    ret.add(new WorkerSlot(id, port));
                }
            }
            return ret;
        }

        @Override
        public void assignSlots(Topologies topologies, Map<String, Collection<WorkerSlot>> newSlotsByTopologyId) {

        }

        @Override
        public String getHostName(Map<String, SupervisorDetails> existingSupervisors, String nodeId) {
            if (existingSupervisors.containsKey(nodeId)) {
                return existingSupervisors.get(nodeId).getHost();
            }
            return null;
        }

        @Override
        public IScheduler getForcedScheduler() {
            return null;
        }
    }
}