com.datastax.driver.core.policies.EC2MultiRegionAddressTranslator Maven / Gradle / Ivy

/*
 * Copyright DataStax, 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.datastax.driver.core.policies;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.exceptions.DriverException;
import com.google.common.annotations.VisibleForTesting;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.util.Enumeration;
import java.util.Hashtable;
import javax.naming.Context;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * {@link AddressTranslator} implementation for a multi-region EC2 deployment where clients are
 * also deployed in EC2.
 *
 * Its distinctive feature is that it translates addresses according to the location of the
 * Cassandra host:
 *
 * 

 *   addresses in different EC2 regions (than the client) are unchanged;
 *   
addresses in the same EC2 region are translated to private IPs.
 * 
 *
 * This optimizes network costs, because Amazon charges more for communication over public IPs.
 *
 * 
 *
 * Implementation note: this class performs a reverse DNS lookup of the origin address, to find
 * the domain name of the target instance. Then it performs a forward DNS lookup of the domain name;
 * the EC2 DNS does the private/public switch automatically based on location.
 */
public class EC2MultiRegionAddressTranslator implements AddressTranslator {

  private static final Logger logger =
      LoggerFactory.getLogger(EC2MultiRegionAddressTranslator.class);

  // TODO when we switch to Netty 4.1, we can replace this with the Netty built-in DNS client
  private final DirContext ctx;

  public EC2MultiRegionAddressTranslator() {
    Hashtable env = new Hashtable();
    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
    try {
      ctx = new InitialDirContext(env);
    } catch (NamingException e) {
      throw new DriverException("Could not create translator", e);
    }
  }

  @VisibleForTesting
  EC2MultiRegionAddressTranslator(DirContext ctx) {
    this.ctx = ctx;
  }

  @Override
  public void init(Cluster cluster) {
    // nothing to do
  }

  @Override
  public InetSocketAddress translate(InetSocketAddress socketAddress) {
    InetAddress address = socketAddress.getAddress();
    try {
      // InetAddress#getHostName() is supposed to perform a reverse DNS lookup, but for some reason
      // it doesn't work
      // within the same EC2 region (it returns the IP address itself).
      // We use an alternate implementation:
      String domainName = lookupPtrRecord(reverse(address));
      if (domainName == null) {
        logger.warn("Found no domain name for {}, returning it as-is", address);
        return socketAddress;
      }

      InetAddress translatedAddress = InetAddress.getByName(domainName);
      logger.debug("Resolved {} to {}", address, translatedAddress);
      return new InetSocketAddress(translatedAddress, socketAddress.getPort());
    } catch (Exception e) {
      logger.warn("Error resolving " + address + ", returning it as-is", e);
      return socketAddress;
    }
  }

  private String lookupPtrRecord(String reversedDomain) throws Exception {
    Attributes attrs = ctx.getAttributes(reversedDomain, new String[] {"PTR"});
    for (NamingEnumeration ae = attrs.getAll(); ae.hasMoreElements(); ) {
      Attribute attr = (Attribute) ae.next();
      for (Enumeration vals = attr.getAll(); vals.hasMoreElements(); )
        return vals.nextElement().toString();
    }
    return null;
  }

  @Override
  public void close() {
    try {
      ctx.close();
    } catch (NamingException e) {
      logger.warn("Error closing translator", e);
    }
  }

  // Builds the "reversed" domain name in the ARPA domain to perform the reverse lookup
  @VisibleForTesting
  static String reverse(InetAddress address) {
    byte[] bytes = address.getAddress();
    if (bytes.length == 4) return reverseIpv4(bytes);
    else return reverseIpv6(bytes);
  }

  private static String reverseIpv4(byte[] bytes) {
    StringBuilder builder = new StringBuilder();
    for (int i = bytes.length - 1; i >= 0; i--) {
      builder.append(bytes[i] & 0xFF).append('.');
    }
    builder.append("in-addr.arpa");
    return builder.toString();
  }

  private static String reverseIpv6(byte[] bytes) {
    StringBuilder builder = new StringBuilder();
    for (int i = bytes.length - 1; i >= 0; i--) {
      byte b = bytes[i];
      int lowNibble = b & 0x0F;
      int highNibble = b >> 4 & 0x0F;
      builder
          .append(Integer.toHexString(lowNibble))
          .append('.')
          .append(Integer.toHexString(highNibble))
          .append('.');
    }
    builder.append("ip6.arpa");
    return builder.toString();
  }
}