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JAVA-1832: Add Ec2MultiRegionAddressTranslator
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‎changelog/README.md‎

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### 4.0.0-alpha4 (in progress)
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- [new feature] JAVA-1832: Add Ec2MultiRegionAddressTranslator
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- [improvement] JAVA-1825: Add remaining Typesafe config primitive types to DriverConfigProfile
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- [new feature] JAVA-1846: Add ConstantReconnectionPolicy
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- [improvement] JAVA-1824: Make policies overridable in profiles

‎core/src/main/java/com/datastax/oss/driver/internal/core/addresstranslation/Ec2MultiRegionAddressTranslator.java‎

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/*
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* Copyright DataStax, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.datastax.oss.driver.internal.core.addresstranslation;
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import com.datastax.oss.driver.api.core.addresstranslation.AddressTranslator;
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import com.datastax.oss.driver.api.core.context.DriverContext;
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import com.datastax.oss.driver.internal.core.util.Loggers;
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import com.datastax.oss.driver.shaded.guava.common.annotations.VisibleForTesting;
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import java.net.InetAddress;
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import java.net.InetSocketAddress;
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import java.util.Enumeration;
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import java.util.Hashtable;
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import javax.naming.Context;
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import javax.naming.NamingEnumeration;
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import javax.naming.NamingException;
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import javax.naming.directory.Attribute;
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import javax.naming.directory.Attributes;
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import javax.naming.directory.DirContext;
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import javax.naming.directory.InitialDirContext;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* {@link AddressTranslator} implementation for a multi-region EC2 deployment <b>where clients are
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* also deployed in EC2</b>.
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*
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* <p>Its distinctive feature is that it translates addresses according to the location of the
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* Cassandra host:
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*
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* <ul>
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* <li>addresses in different EC2 regions (than the client) are unchanged;
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* <li>addresses in the same EC2 region are <b>translated to private IPs</b>.
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* </ul>
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*
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* This optimizes network costs, because Amazon charges more for communication over public IPs.
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*
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* <p>Implementation note: this class performs a reverse DNS lookup of the origin address, to find
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* the domain name of the target instance. Then it performs a forward DNS lookup of the domain name;
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* the EC2 DNS does the private/public switch automatically based on location.
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*/
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public class Ec2MultiRegionAddressTranslator implements AddressTranslator {
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private static final Logger LOG = LoggerFactory.getLogger(Ec2MultiRegionAddressTranslator.class);
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private final DirContext ctx;
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private final String logPrefix;
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public Ec2MultiRegionAddressTranslator(@SuppressWarnings("unused") DriverContext context) {
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this.logPrefix = context.sessionName();
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@SuppressWarnings("JdkObsolete")
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Hashtable<Object, Object> env = new Hashtable<>();
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env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
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try {
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ctx = new InitialDirContext(env);
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} catch (NamingException e) {
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throw new RuntimeException("Could not create translator", e);
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}
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}
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@VisibleForTesting
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Ec2MultiRegionAddressTranslator(DirContext ctx) {
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this.logPrefix = "test";
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this.ctx = ctx;
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}
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@Override
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public InetSocketAddress translate(InetSocketAddress socketAddress) {
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InetAddress address = socketAddress.getAddress();
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try {
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// InetAddress#getHostName() is supposed to perform a reverse DNS lookup, but for some reason
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// it doesn't work within the same EC2 region (it returns the IP address itself).
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// We use an alternate implementation:
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String domainName = lookupPtrRecord(reverse(address));
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if (domainName == null) {
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LOG.warn("[{}] Found no domain name for {}, returning it as-is", logPrefix, address);
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return socketAddress;
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}
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InetAddress translatedAddress = InetAddress.getByName(domainName);
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LOG.debug("[{}] Resolved {} to {}", logPrefix, address, translatedAddress);
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return new InetSocketAddress(translatedAddress, socketAddress.getPort());
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} catch (Exception e) {
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Loggers.warnWithException(
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LOG, "[{}] Error resolving {}, returning it as-is", logPrefix, address, e);
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return socketAddress;
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}
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}
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private String lookupPtrRecord(String reversedDomain) throws Exception {
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Attributes attrs = ctx.getAttributes(reversedDomain, new String[] {"PTR"});
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for (NamingEnumeration ae = attrs.getAll(); ae.hasMoreElements(); ) {
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Attribute attr = (Attribute) ae.next();
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Enumeration<?> vals = attr.getAll();
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if (vals.hasMoreElements()) {
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return vals.nextElement().toString();
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}
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}
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return null;
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}
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@Override
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public void close() {
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try {
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ctx.close();
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} catch (NamingException e) {
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Loggers.warnWithException(LOG, "Error closing translator", e);
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}
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}
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// Builds the "reversed" domain name in the ARPA domain to perform the reverse lookup
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@VisibleForTesting
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static String reverse(InetAddress address) {
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byte[] bytes = address.getAddress();
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if (bytes.length == 4) return reverseIpv4(bytes);
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else return reverseIpv6(bytes);
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}
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private static String reverseIpv4(byte[] bytes) {
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StringBuilder builder = new StringBuilder();
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for (int i = bytes.length - 1; i >= 0; i--) {
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builder.append(bytes[i] & 0xFF).append('.');
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}
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builder.append("in-addr.arpa");
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return builder.toString();
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}
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private static String reverseIpv6(byte[] bytes) {
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StringBuilder builder = new StringBuilder();
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for (int i = bytes.length - 1; i >= 0; i--) {
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byte b = bytes[i];
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int lowNibble = b & 0x0F;
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int highNibble = b >> 4 & 0x0F;
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builder
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.append(Integer.toHexString(lowNibble))
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.append('.')
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.append(Integer.toHexString(highNibble))
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.append('.');
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}
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builder.append("ip6.arpa");
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return builder.toString();
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}
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}

‎core/src/test/java/com/datastax/oss/driver/internal/core/addresstranslation/Ec2MultiRegionAddressTranslatorTest.java‎

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/*
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* Copyright DataStax, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.datastax.oss.driver.internal.core.addresstranslation;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.mockito.Mockito.any;
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import static org.mockito.Mockito.anyString;
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import static org.mockito.Mockito.mock;
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import static org.mockito.Mockito.times;
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import static org.mockito.Mockito.verify;
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import static org.mockito.Mockito.when;
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import java.net.InetAddress;
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import java.net.InetSocketAddress;
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import javax.naming.NamingException;
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import javax.naming.directory.BasicAttributes;
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import javax.naming.directory.InitialDirContext;
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import org.junit.Test;
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public class Ec2MultiRegionAddressTranslatorTest {
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@Test
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public void should_return_same_address_when_no_entry_found() throws Exception {
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InitialDirContext mock = mock(InitialDirContext.class);
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when(mock.getAttributes(anyString(), any(String[].class))).thenReturn(new BasicAttributes());
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Ec2MultiRegionAddressTranslator translator = new Ec2MultiRegionAddressTranslator(mock);
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InetSocketAddress address = new InetSocketAddress("192.0.2.5", 9042);
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assertThat(translator.translate(address)).isEqualTo(address);
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}
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@Test
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public void should_return_same_address_when_exception_encountered() throws Exception {
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InitialDirContext mock = mock(InitialDirContext.class);
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when(mock.getAttributes(anyString(), any(String[].class)))
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.thenThrow(new NamingException("Problem resolving address (not really)."));
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Ec2MultiRegionAddressTranslator translator = new Ec2MultiRegionAddressTranslator(mock);
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InetSocketAddress address = new InetSocketAddress("192.0.2.5", 9042);
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assertThat(translator.translate(address)).isEqualTo(address);
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}
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@Test
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public void should_return_new_address_when_match_found() throws Exception {
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InetSocketAddress expectedAddress = new InetSocketAddress("54.32.55.66", 9042);
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InitialDirContext mock = mock(InitialDirContext.class);
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when(mock.getAttributes("5.2.0.192.in-addr.arpa", new String[] {"PTR"}))
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.thenReturn(new BasicAttributes("PTR", expectedAddress.getHostName()));
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Ec2MultiRegionAddressTranslator translator = new Ec2MultiRegionAddressTranslator(mock);
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InetSocketAddress address = new InetSocketAddress("192.0.2.5", 9042);
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assertThat(translator.translate(address)).isEqualTo(expectedAddress);
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}
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@Test
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public void should_close_context_when_closed() throws Exception {
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InitialDirContext mock = mock(InitialDirContext.class);
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Ec2MultiRegionAddressTranslator translator = new Ec2MultiRegionAddressTranslator(mock);
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// ensure close has not been called to this point.
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verify(mock, times(0)).close();
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translator.close();
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// ensure close is closed.
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verify(mock).close();
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}
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@Test
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public void should_build_reversed_domain_name_for_ip_v4() throws Exception {
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InetAddress address = InetAddress.getByName("192.0.2.5");
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assertThat(Ec2MultiRegionAddressTranslator.reverse(address))
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.isEqualTo("5.2.0.192.in-addr.arpa");
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}
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@Test
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public void should_build_reversed_domain_name_for_ip_v6() throws Exception {
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InetAddress address = InetAddress.getByName("2001:db8::567:89ab");
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assertThat(Ec2MultiRegionAddressTranslator.reverse(address))
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.isEqualTo("b.a.9.8.7.6.5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa");
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}
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}

‎manual/core/address_resolution/README.md‎

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```java
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public class MyAddressTranslator implements AddressTranslator {
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public PassThroughAddressTranslator(DriverContext context, DriverOption configRoot) {
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// retrieve any required dependency or extra configuration option, otherwise can stay empty
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}
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public InetSocketAddress translate(InetSocketAddress address) {
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// your custom translation logic
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}
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@Override
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public void close() {
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// free any resources if needed, otherwise can stay empty
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```
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datastax-java-driver.address-translator.class = com.mycompany.MyAddressTranslator
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```
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```
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Note: the contact points provided while creating the `CqlSession` are not translated, only addresses
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retrieved from or sent by Cassandra nodes are.
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<!-- TODO ec2 multi-region translator -->
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### EC2 multi-region
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If you deploy both Cassandra and client applications on Amazon EC2, and your cluster spans multiple regions, you'll have
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to configure your Cassandra nodes to broadcast public RPC addresses.
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However, this is not always the most cost-effective: if a client and a node are in the same region, it would be cheaper
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to connect over the private IP. Ideally, you'd want to pick the best address in each case.
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The driver provides [Ec2MultiRegionAddressTranslator] which does exactly that. To use it, specify the following in
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the [configuration](../configuration/):
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```
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datastax-java-driver.address-translator.class = Ec2MultiRegionAddressTranslator
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```
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With this configuration, you keep broadcasting public RPC addresses. But each time the driver connects to a new
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Cassandra node:
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* if the node is *in the same EC2 region*, the public IP will be translated to the intra-region private IP;
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* otherwise, it will not be translated.
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(To achieve this, `Ec2MultiRegionAddressTranslator` performs a reverse DNS lookup of the origin address, to find the
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domain name of the target instance. Then it performs a forward DNS lookup of the domain name; the EC2 DNS does the
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private/public switch automatically based on location).
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[AddressTranslator]: http://docs.datastax.com/en/drivers/java/4.0/com/datastax/oss/driver/api/core/addresstranslation/AddressTranslator.html
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[Ec2MultiRegionAddressTranslator]: http://docs.datastax.com/en/drivers/java/4.0/com/datastax/oss/driver/internal/core/addresstranslation/Ec2MultiRegionAddressTranslator.html
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[cassandra.yaml]: https://docs.datastax.com/en/cassandra/3.x/cassandra/configuration/configCassandra_yaml.html
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[rpc_address]: https://docs.datastax.com/en/cassandra/3.x/cassandra/configuration/configCassandra_yaml.html?scroll=configCassandra_yaml__rpc_address

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