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https://issues.apache.org/jira/browse/HBASE-30376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18114111#comment-18114111
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Longping Jie commented on HBASE-30376:
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I currently don't see a local DNS caching mechanism in the client. We've
recently encountered instability with the DNS server, which can cause
fluctuations lasting one or two minutes. Therefore, we hope to cache DNS
mappings and, during fluctuations, downgrade to the previous cycle's cached
data. I can submit a PR first, and you can help review the code. Then we can
discuss whether the existing mechanism can avoid my issue, trying not to change
the hbase-client's code as much as possible.
> 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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