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ZOOKEEPER-4956: Provide a HostProvider that uses DNS SRV record for dynamic server discovery #2320

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ZOOKEEPER-4956: Provide a HostProvider that uses DNS SRV record for dynamic server discovery #2320

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@li4wang li4wang commented Sep 27, 2025 •
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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:

  1. DnsSrvHostProvider: New HostProvider implementation that performs DNS SRV lookups to discover ZooKeeper servers
  2. HostConnectionManager: Extracted connection management and reconfiguration logic from StaticHostProvider into a reusable component
  3. StaticHostProvider Refactoring: Modified to use HostConnectionManager for consistent connection handling across providers
  4. ConnectionType: New enum that represents the type of connection resolutions
  5. Configuration: Added zookeeper.hostProvider.dnsSrvRefreshIntervalMs client property for DNS refresh intervals

@li4wang li4wang mentioned this pull request Sep 29, 2025
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anmolnar
anmolnar requested changes Oct 15, 2025
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Where are the changes of StaticHostProvider?

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anmolnar reviewed Oct 15, 2025
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li4wang commented Dec 15, 2025

Where are the changes of StaticHostProvider?

I thought it would be better to check in the updated StaticHostProvider later in a separate PR, as the changes are code refactoring, so I took it out from this PR.

However, I noticed that StaticHostProvider is mentioned in the summary of this PR, let me just added it back to avoid any confusion.

@li4wang li4wang force-pushed the ZOOKEEPER-4956 branch 8 times, most recently from dc2bfe6 to 6e01933 Compare December 17, 2025 03:54
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li4wang commented Dec 17, 2025

Hi @anmolnar, thanks a lot for your feedback. I've responded to all the comments. Can you please take a look at the updated PR? Thanks.

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anmolnar requested changes Dec 18, 2025
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Just a few more comments, otherwise looks good to me.

zookeeper-server/src/main/java/org/apache/zookeeper/client/HostProvider.java Outdated
*
* @return the ConnectionType supported by this provider
*/
default ConnectionType getSupportedConnectionType() {
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Where do you use this new field? Why is this information important?

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@li4wang li4wang Dec 24, 2025

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Removed, not needed any more.

zookeeper-server/src/main/java/org/apache/zookeeper/client/ConnectionType.java Outdated
* This is an internal enum used for connection string and provider validation.
*/
@InterfaceAudience.Private
public enum ConnectionType {
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I can't find usages of this new type in your code.

@li4wang li4wang force-pushed the ZOOKEEPER-4956 branch 4 times, most recently from 757b86d to 654c6c1 Compare December 19, 2025 08:00
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anmolnar commented Dec 19, 2025

Please see my comments on the other pr #2321
I think we should merge these patches into a single one.

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li4wang commented Dec 19, 2025

I think we should merge these patches into a single one.

Yes, working on merging #2321 into this one right now.

@li4wang li4wang force-pushed the ZOOKEEPER-4956 branch 5 times, most recently from d101e10 to c5449f8 Compare December 23, 2025 00:31
ZOOKEEPER-4956: Provide a HostProvider that uses DNS SRV record for d…
1c5c292 
…ynamic server discovery

Author: Li Wang <liwang@apple.com>
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