com.twitter.distributedlog.net.DNSResolver Maven / Gradle / Ivy
/**
* 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 com.twitter.distributedlog.net;
import org.apache.bookkeeper.net.DNSToSwitchMapping;
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* Abstract DNS resolver for bookkeeper ensemble placement.
*/
public abstract class DNSResolver implements DNSToSwitchMapping {
static final Logger LOG = LoggerFactory.getLogger(DNSResolver.class);
protected final ConcurrentMap domainNameToNetworkLocation =
new ConcurrentHashMap();
protected final ConcurrentMap hostNameToRegion =
new ConcurrentHashMap();
/**
* Construct the default dns resolver without host-region overrides.
*/
public DNSResolver() {
this("");
}
/**
* Construct the dns resolver with host-region overrides.
*
* hostRegionOverrides is a string of pairs of host-region mapping
* (host:region) separated by ';'. during dns resolution, the host will be resolved
* to override region. example: host1:region1;host2:region2;...
*
* @param hostRegionOverrides
* pairs of host-region mapping separated by ';'
*/
public DNSResolver(String hostRegionOverrides) {
if (StringUtils.isNotBlank(hostRegionOverrides)) {
// Host Region Overrides are of the form
// HN1:R1;HN2:R2;...
String[] overrides = hostRegionOverrides.split(";");
for (String override : overrides) {
String[] parts = override.split(":");
if (parts.length != 2) {
LOG.warn("Incorrect override specified", override);
} else {
hostNameToRegion.putIfAbsent(parts[0], parts[1]);
}
}
} // otherwise, no overrides were specified
}
/**
* {@inheritDoc}
*/
@Override
public List resolve(List names) {
List networkLocations = new ArrayList(names.size());
for (String name : names) {
networkLocations.add(resolve(name));
}
return networkLocations;
}
private String resolve(String domainName) {
String networkLocation = domainNameToNetworkLocation.get(domainName);
if (null == networkLocation) {
networkLocation = resolveToNetworkLocation(domainName);
domainNameToNetworkLocation.put(domainName, networkLocation);
}
return networkLocation;
}
/**
* Resolve the domainName to its network location.
*
* @param domainName
* domain name
* @return the network location of domainName
*/
protected abstract String resolveToNetworkLocation(String domainName);
/**
* {@inheritDoc}
*/
@Override
public void reloadCachedMappings() {
domainNameToNetworkLocation.clear();
}
}