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[FLINK-38754][runtime] Avoid reverse DNS lookups when connecting to BlobServer #27318

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Merged
zhuzhurk merged 1 commit into from
Dec 10, 2025
+5 −3
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[FLINK-38754][runtime] Avoid reverse DNS lookups when connecting to BlobServer #27318

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8 changes: 5 additions & 3 deletions flink-runtime/src/main/java/org/apache/flink/runtime/blob/BlobClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -92,10 +92,12 @@ public BlobClient(InetSocketAddress serverAddress, Configuration clientConfig)
}

// Establish the socket using the hostname and port. This avoids a potential issue where
// the
// InetSocketAddress can cache a failure in hostname resolution forever.
// the InetSocketAddress can cache a failure in hostname resolution forever.
// Use getHostString() instead of getHostName() to avoid unnecessary reverse DNS and DNS
// lookups when addresses are specified as IP literals. This improves reliability and
// reduces latency for each blob transfer.
socket.connect(
new InetSocketAddress(serverAddress.getHostName(), serverAddress.getPort()),
new InetSocketAddress(serverAddress.getHostString(), serverAddress.getPort()),
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@davidradl davidradl Dec 4, 2025

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The change looks good. nit: I wonder if we could add a comment to explain why we do. not use getHostName. Maybe include some of the following reasons: Addresses are often configured as IP addresses for reliability
DNS may be unavailable or slow in containerized/cloud environments
Every blob transfer would trigger unnecessary reverse DNS lookups
Connection failures could occur if DNS resolution fails

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@eemario eemario Dec 8, 2025

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Thanks for the suggestion! I’ve updated the code comment to explain the reason.

clientConfig.get(BlobServerOptions.CONNECT_TIMEOUT));
socket.setSoTimeout(clientConfig.get(BlobServerOptions.SO_TIMEOUT));
} catch (Exception e) {
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