ZOOKEEPER-4956: Provide a HostProvider that uses DNS SRV record for dynamic server discovery #2320
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…ynamic server discovery Author: Li Wang <[email protected]>
| final String absoluteDnsName = trimmedDnsName.endsWith(".") ? trimmedDnsName : trimmedDnsName + "."; | ||
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| try { | ||
| Name.fromString(absoluteDnsName); |
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You can do a lookup immediately in order to validate that the DNS name has valid SRV record.
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| * @return the initialized Timer or null if refresh interval is 0 or negative | ||
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| private Timer initializeDnsRefreshTimer() { |
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I don't think you need this internal caching thing at all in ZooKeeper. DNS has its own multi-layer caching logic in the IP stack of the operating system and at the DNS resolver servers. Just query the SRV entry every time you run out of available servers and DNS will take care of the rest. There's not much benefit in caching something which is already cached in the host's memory.
| import org.slf4j.LoggerFactory; | ||
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| /** | ||
| * HostConnectionManager handles the complex connection management and reconfiguration logic |
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I'd rather explain the connection management logic in detail in Javadoc. "handles complex logic" is meaningless.
| <scope>compile</scope> | ||
| </dependency> | ||
| <dependency> | ||
| <groupId>dnsjava</groupId> |
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Isn't there standard Java API for this which is not third party?
| * HostConnectionManager handles the complex connection management and reconfiguration logic | ||
| */ | ||
| @InterfaceAudience.Private | ||
| public final class HostConnectionManager { |
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This could be the common abstract class for both implementations. Doing it with inheritance might be simpler than this composition where you just forward the calls to Connection Manager.
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The existing ZooKeeper client architecture relies on StaticHostProvider, which lacks auto service discovery capabilities and must wait for external mechanisms to push server list updates, either through manual configuration changes or reconfig notifications.
This PR provides a HostProvider implementation that performs dynamic service discovery based on DNS SRV record. The following is a summary of the changes: