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https://issues.apache.org/jira/browse/FLINK-10213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16768104#comment-16768104
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Stephan Ewen commented on FLINK-10213:
--------------------------------------
I agree with @Joey Echeverria here. Any caching of resolved results in Flink is
a bit tricky.
Simply always ging again with the host name would be safe. There is still
caching done in the OS, so there not always DNS lookups, but these caches are
invalidated properly.
The solution of simply going with the hostname seems simple and should work.
Unless we see a serious performance/overhead issue here, I would favor the
simplicity of the approach.
One thing that would be great is to have a test guarding this behavior.
Otherwise I can see someone in the future wanting to optimize the code and
thereby changing the behavior again.
> Task managers cache a negative DNS lookup of the blob server indefinitely
> -------------------------------------------------------------------------
>
> Key: FLINK-10213
> URL: https://issues.apache.org/jira/browse/FLINK-10213
> Project: Flink
> Issue Type: Bug
> Components: TaskManager
> Affects Versions: 1.5.0
> Reporter: Joey Echeverria
> Assignee: Joey Echeverria
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.8.0
>
>
> When the task manager establishes a connection with the resource manager, it
> gets the hostname and port of the blob server and uses that to create an
> instance of an {{InetSocketAddress}}. Per the documentation of the
> constructor:
> {quote}An attempt will be made to resolve the hostname into an InetAddress.
> If that attempt fails, the address will be flagged as _unresolved_{quote}
> Flink never checks to see if the address was unresolved. Later when executing
> a task that needs to download from the blob server, it will use that same
> {{InetSocketAddress}} instance to attempt to connect a {{Socket}}. This will
> result in an exception similar to:
> {noformat}
> java.io.IOException: Failed to fetch BLOB
> 97799b827ef073e04178a99f0f40b00e/p-6d8ec2ad31337110819c7c3641fdb18d3793a7fb-72bf00066308f4b4d2a9c5aea593b41f
> from jobmanager:6124 and store it under
> /tmp/blobStore-d135961a-03cb-4542-af6d-cf378ff83c12/incoming/temp-00018669
> at
> org.apache.flink.runtime.blob.BlobClient.downloadFromBlobServer(BlobClient.java:191)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.blob.AbstractBlobCache.getFileInternal(AbstractBlobCache.java:181)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.blob.PermanentBlobCache.getFile(PermanentBlobCache.java:206)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.execution.librarycache.BlobLibraryCacheManager.registerTask(BlobLibraryCacheManager.java:120)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.taskmanager.Task.createUserCodeClassloader(Task.java:863)
> [flink-dist_2.11-1.5.0.jar:1.5.0]
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:579)
> [flink-dist_2.11-1.5.0.jar:1.5.0]
> at java.lang.Thread.run(Thread.java:748) [?:1.8.0_171]
> Caused by: java.io.IOException: Could not connect to BlobServer at address
> flink-jobmanager:6124
> at org.apache.flink.runtime.blob.BlobClient.<init>(BlobClient.java:124)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.blob.BlobClient.downloadFromBlobServer(BlobClient.java:165)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> ... 6 more
> Caused by: java.net.UnknownHostException: jobmanager
> at
> java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
> ~[?:1.8.0_171]
> at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
> ~[?:1.8.0_171]
> at java.net.Socket.connect(Socket.java:589) ~[?:1.8.0_171]
> at java.net.Socket.connect(Socket.java:538) ~[?:1.8.0_171]
> at org.apache.flink.runtime.blob.BlobClient.<init>(BlobClient.java:118)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> at
> org.apache.flink.runtime.blob.BlobClient.downloadFromBlobServer(BlobClient.java:165)
> ~[flink-dist_2.11-1.5.0.jar:1.5.0]
> ... 6 more
> {noformat}
> Since the {{InetSocketAddress}} is re-used, you'll have repeated failures of
> any tasks that are executed on that task manager and the only current
> workaround is to manually restart the task manager.
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