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https://issues.apache.org/jira/browse/HBASE-30376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18113814#comment-18113814
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Daniel Roudnitsky commented on HBASE-30376:
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Hi Longping, I’m not convinced HBase should maintain its own DNS cache here.
Could stale answer behavior can be provided by the system resolver, for example
Unbound with serve-expired, without adding another cache above the JVM and OS
resolver ?
> Tolerate transient DNS server failures with an opt-in client-side DNS
> resolution cache (serve-stale fallback) for RPC connections
> ---------------------------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-30376
> URL: https://issues.apache.org/jira/browse/HBASE-30376
> Project: HBase
> Issue Type: Improvement
> Components: Client
> Affects Versions: 2.6.7
> Reporter: Longping Jie
> Assignee: Longping Jie
> Priority: Major
>
> **Problem**
> The client resolves RegionServer/Master hostnames via `java.net.InetAddress`
> whenever a new RPC connection is established, and twice more in the Kerberos
> security preamble (a second forward lookup plus a PTR lookup for principal
> `_HOST`). When the DNS server is intermittently unstable, new connections
> fail with `UnknownHostException` until DNS recovers (retry window is only
> tens of seconds), the blocking lookup stalls the Netty event loop and all
> connections sharing it, and Kerberos connections fail on PTR lookups even
> when TCP connect succeeded.
> **Fix**
> Add an opt-in cache in hbase-client with serve-stale semantics: live DNS
> always first; on resolution failure fall back to the last successful mapping,
> age-bounded (default 10 min) and kept fresh by a daemon background refresher
> (degraded hosts re-probed every 2s); when no usable cache exists, throw the
> original `UnknownHostException` unchanged. Two hook points only
> (`RpcConnection#getRemoteInetAddress`, `RpcConnection#getServerPrincipals`),
> so Kerberos and non-Kerberos behave the same. No server-side or wire-protocol
> changes, no new dependencies, JDK 8/17 compatible. Gated by
> `hbase.ipc.client.dns.fallback-cache.enabled` (default `false` = original
> code path).
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