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   * 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
   *
   *     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.cassandra.locator;
  
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.Set;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import org.apache.cassandra.exceptions.ConfigurationException;
  import org.apache.cassandra.tcm.ClusterMetadata;
  import org.apache.cassandra.tcm.membership.Location;
  
  public class Ec2LocationProvider extends CloudMetadataLocationProvider
  {
      static final String SNITCH_PROP_NAMING_SCHEME = "ec2_naming_scheme";
      static final String EC2_NAMING_LEGACY = "legacy";
      static final String EC2_NAMING_STANDARD = "standard";
  
      @VisibleForTesting
      public static final String ZONE_NAME_QUERY = "/latest/meta-data/placement/availability-zone";
  
      private final boolean usingLegacyNaming;
  
      /**
       * Used via reflection by DatabaseDescriptor::createInitialLocationProvider
       */
      public Ec2LocationProvider() throws IOException, ConfigurationException
      {
          this(new SnitchProperties());
      }
  
      public Ec2LocationProvider(SnitchProperties props) throws IOException, ConfigurationException
      {
          this(Ec2MetadataServiceConnector.create(props));
      }
  
      Ec2LocationProvider(AbstractCloudMetadataServiceConnector connector) throws IOException
      {
          super(connector, Ec2LocationProvider::getLocation);
          usingLegacyNaming = isUsingLegacyNaming(connector.getProperties());
      }
  
      private static Location getLocation(AbstractCloudMetadataServiceConnector connector) throws IOException
      {
          // if using the full naming scheme, region name is created by removing letters from the
          // end of the availability zone and zone is the full zone name
          boolean usingLegacyNaming = isUsingLegacyNaming(connector.getProperties());
  
          String az = connector.apiCall(ZONE_NAME_QUERY);
          String region;
          String localDc;
          String localRack;
          if (usingLegacyNaming)
          {
              // Split "us-east-1a" or "asia-1a" into "us-east"/"1a" and "asia"/"1a".
              String[] splits = az.split("-");
              localRack = splits[splits.length - 1];
  
              // hack for CASSANDRA-4026
              region = az.substring(0, az.length() - 1);
              if (region.endsWith("1"))
                  region = az.substring(0, az.length() - 3);
          }
          else
          {
              // grab the region name, which is embedded in the availability zone name.
              // thus an AZ of "us-east-1a" yields the region name "us-east-1"
              region = az.replaceFirst("[a-z]+$","");
              localRack = az;
          }
  
          localDc = region.concat(connector.getProperties().getDcSuffix());
  
          return new Location(localDc, localRack);
      }
  
      private static boolean isUsingLegacyNaming(SnitchProperties props)
      {
          return props.get(SNITCH_PROP_NAMING_SCHEME, EC2_NAMING_STANDARD).equalsIgnoreCase(EC2_NAMING_LEGACY);
      }
  
      public void validate(ClusterMetadata metadata)
      {
          // Validate that the settings here match what was used to locate
          // and register other nodes in the cluster (if there are any)
          Set<String> datacenters = metadata.directory.allDatacenterRacks().keySet();
          Set<String> racks = new HashSet<>();
          for (String dc : datacenters)
              racks.addAll(metadata.directory.datacenterRacks(dc).keySet());
          validate(datacenters, racks);
      }
  
      public boolean validate(Set<String> datacenters, Set<String> racks)
      {
          boolean valid = true;
  
          for (String dc : datacenters)
          {
              // predicated on the late-2017 AWS naming 'convention' that all region names end with a digit.
              // Unfortunately, life isn't that simple. Since we allow custom datacenter suffixes (CASSANDRA-5155),
              // an operator could conceiveably make the suffix "a", and thus create a region name that looks just like
              // one of the region's availability zones. (for example, "us-east-1a").
              // Further, we can't make any assumptions of what that suffix might be by looking at this node's
              // datacenterSuffix as conceivably their could be many different suffixes in play for a given region.
              //
              // It is impossible to distinguish standard and legacy names for datacenters in some cases
              // as the format didn't change for some regions (us-west-2 for example).
              // We can still identify as legacy the dc names without a number as a suffix like us-east"
              boolean dcUsesLegacyFormat = dc.matches("^[a-z]+-[a-z]+$");
              if (dcUsesLegacyFormat && !usingLegacyNaming)
              {
                  valid = false;
                  break;
              }
          }
  
          for (String rack : racks)
          {
              // predicated on late-2017 AWS naming 'convention' that AZs do not have a digit as the first char -
              // we had that in our legacy AZ (rack) names. Thus we test to see if the rack is in the legacy format.
              //
              // NOTE: the allowed custom suffix only applies to datacenter (region) names, not availability zones.
              boolean rackUsesLegacyFormat = rack.matches("[\\d][a-z]");
              if (rackUsesLegacyFormat != usingLegacyNaming)
              {
                  valid = false;
                  break;
              }
          }
  
          if (!valid)
          {
              throw new ConfigurationException(String.format("This ec2-enabled location provider appears to be using the " +
                                                             "%s naming scheme for regions, but existing nodes in cluster " +
                                                             "are using the opposite: " +
                                                             "region(s) = %s, availability zone(s) = %s. " +
                                                             "Please check the %s property in the %s configuration file " +
                                                             "for more details.",
                                                             usingLegacyNaming ? "legacy" : "standard", datacenters, racks,
                                                             SNITCH_PROP_NAMING_SCHEME, SnitchProperties.RACKDC_PROPERTY_FILENAME));
          }
          return true;
      }
  }
  