Add hadoop-topology module with SwitchableDNSToSwitchMapping and Topo… - #81
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…logyServerDNSToSwitchMapping implementations
SaadASTheDev
commented
Sep 16, 2026
| * to {@link TopologyServerDNSToSwitchMapping} when {@code net.topology.server.enabled} | ||
| * is true, otherwise the stock {@link ScriptBasedMapping}. | ||
| */ | ||
| public class SwitchableDNSToSwitchMapping extends AbstractDNSToSwitchMapping { |
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SwitchableDNS uses the mentioned config overide to point to this class for script vs server delegation, or else the class would default to script only
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gonna change this as per the convo
SaadASTheDev
commented
Sep 16, 2026
| super.setConf(conf); | ||
| boolean useServer = conf != null | ||
| && conf.getBoolean(SERVER_ENABLED_KEY, SERVER_ENABLED_DEFAULT); | ||
| if (useServer) { |
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this is the crux of how we switch, read the respective config ans set delegate to the valid class "TopologyServer..." here
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In order to work with the topology server (the sidecar), the NameNode needs a way to resolve rack topology by calling it over HTTP rather than forking the topology script. This is done with two classes: SwitchableDNSToSwitchMapping, which the NameNode is pointed at via
net.topology.node.switch.mapping.impland which dispatches to either the stock forked topology script (ScriptBasedMapping) or the topology server so the NameNode resolves agnostically, and TopologyServerDNSToSwitchMapping, the class it delegates to for the server path that actually makes the HTTP GET call to the sidecar. The choice between the two is driven by thenet.topology.server.enabled flag: false, the default, keeps the stock script behavior, and true routes lookups to the server so enabling it or rolling back is just a flag flip rather than a config-class change. Caching and default-rack fallback are unchanged from the script path: they stay in the NameNode via Hadoop's CachedDNSToSwitchMapping, and the server itself holds no cache. The topology server is then enabled via net.topology.server.enabled=true, set in hdfs-site.xmlNOTICE
Please create an issue in ASF JIRA before opening a pull request,
and you need to set the title of the pull request which starts with
the corresponding JIRA issue number. (e.g. HADOOP-XXXXX. Fix a typo in YYY.)
For more details, please see https://cwiki.apache.org/confluence/display/HADOOP/How+To+Contribute