/*
* Copyright (C) 2012-2015 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 org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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 java.net.InetAddress;
import java.net.InetSocketAddress;
import java.util.Enumeration;
import java.util.Hashtable;
/**
* {@link AddressTranslator} implementation for a multi-region EC2 deployment <b>where clients are also deployed in EC2</b>.
* <p/>
* Its distinctive feature is that it translates addresses according to the location of the Cassandra host:
* <ul>
* <li>addresses in different EC2 regions (than the client) are unchanged;</li>
* <li>addresses in the same EC2 region are <b>translated to private IPs</b>.</li>
* </ul>
* This optimizes network costs, because Amazon charges more for communication over public IPs.
* <p/>
* <p/>
* 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<Object, Object> env = new Hashtable<Object, Object>();
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();
}
}