joey commented on a change in pull request #6862: [FLINK-10213] Task managers
cache a negative DNS lookup of the blob server indefinitely
URL: https://github.com/apache/flink/pull/6862#discussion_r240666825
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/blob/BlobClient.java
##########
@@ -87,12 +87,13 @@ public BlobClient(InetSocketAddress serverAddress,
Configuration clientConfig) t
LOG.info("Using ssl connection to the blob
server");
socket =
SSLUtils.createSSLClientSocketFactory(clientConfig).createSocket(
- serverAddress.getAddress(),
+ serverAddress.getHostName(),
serverAddress.getPort());
}
else {
- socket = new Socket();
- socket.connect(serverAddress);
+ // Establish the socket using the hostname and
port. This avoids a potential issue where the
+ // InetSocketAddress can cache a failure in
hostname resolution forever.
+ socket = new
Socket(serverAddress.getHostName(), serverAddress.getPort());
Review comment:
We can do that, but I'm not sure it's the best idea. Since the resolution in
`InetSocketAddress` only happens when the object is instantiated, you could
cache an old name resolution. The most likely reason for this to happen would
be a deployment environment such as Kubernetes. If the JobManger pod is
restarted, then a new pod will take over and will get assigned a new IP
address. Kubernetes will automatically update the DNS entry using KubeDNS for
the service name. I think that means you could have a situation where the
`InetSocketAdress` says it's resolved, but it cached an old resolution. The
safest thing is to force the DNS resolution when we make the connection. Both
Java and the kernel will already cache the DNS entry based on the TTL in the
DSN record, so I don't think we gain much by adding an additional caching layer
in the `InetSocketAddress` itself.
Let me know if you agree or if we should still consider the change.
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