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Ravi Prakash edited comment on HADOOP-15129 at 12/12/18 11:10 AM: ------------------------------------------------------------------ Hi Karthik! Thanks for your contribution. Could you please rebase the patch to the latest trunk? I usually apply patches using {code:java} $ git apply <patch-file>{code} A few suggestions: # Could you please use short descriptions in JIRA? [I was told a long time ago|https://issues.apache.org/jira/browse/HDFS-2011?focusedCommentId=13041707&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13041707]. :) # When using JIRA numbers, could you please write HDFS-8068 (instead of just 8068) because issues often cut across several different projects, and this way JIRA creates nice links for viewers to click on? Patches are usually committed to trunk *first* and then a (possibly) different version of the patch may be committed to earlier branches like branch-2. So technically you could have used neat Lambdas in the trunk patch. ;) Its a nit though. I'm trying to find the wikipage that tried to explain certain errors. I'm afraid I rarely found them useful (its probably because we didn't really expand on those wiki pages ever), so I'm fine with a more helpful error in the logs. was (Author: raviprak): Hi Karthik! Thanks for your contribution. Could you please rebase the patch to the latest trunk? I usually apply patches using {code:java} $ git apply <patch-file>{code} A few suggestions: # Could you please use short descriptions in JIRA? I was told a long time ago. :) # When using JIRA numbers, could you please write HDFS-8068 (instead of just 8068) because issues often cut across several different projects, and this way JIRA creates nice links for viewers to click on? Patches are usually committed to trunk *first* and then a (possibly) different version of the patch may be committed to earlier branches like branch-2. So technically you could have used neat Lambdas in the trunk patch. ;) Its a nit though. I'm trying to find the wikipage that tried to explain certain errors. I'm afraid I rarely found them useful (its probably because we didn't really expand on those wiki pages ever), so I'm fine with a more helpful error in the logs. > Datanode caches namenode DNS lookup failure and cannot startup > -------------------------------------------------------------- > > Key: HADOOP-15129 > URL: https://issues.apache.org/jira/browse/HADOOP-15129 > Project: Hadoop Common > Issue Type: Bug > Components: ipc > Affects Versions: 2.8.2 > Environment: Google Compute Engine. > I'm using Java 8, Debian 8, Hadoop 2.8.2. > Reporter: Karthik Palaniappan > Assignee: Karthik Palaniappan > Priority: Minor > Attachments: HADOOP-15129.001.patch, HADOOP-15129.002.patch > > > On startup, the Datanode creates an InetSocketAddress to register with each > namenode. Though there are retries on connection failure throughout the > stack, the same InetSocketAddress is reused. > InetSocketAddress is an interesting class, because it resolves DNS names to > IP addresses on construction, and it is never refreshed. Hadoop re-creates an > InetSocketAddress in some cases just in case the remote IP has changed for a > particular DNS name: https://issues.apache.org/jira/browse/HADOOP-7472. > Anyway, on startup, you cna see the Datanode log: "Namenode...remains > unresolved" -- referring to the fact that DNS lookup failed. > {code:java} > 2017-11-02 16:01:55,115 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: > Refresh request received for nameservices: null > 2017-11-02 16:01:55,153 WARN org.apache.hadoop.hdfs.DFSUtilClient: Namenode > for null remains unresolved for ID null. Check your hdfs-site.xml file to > ensure namenodes are configured properly. > 2017-11-02 16:01:55,156 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: > Starting BPOfferServices for nameservices: <default> > 2017-11-02 16:01:55,169 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: > Block pool <registering> (Datanode Uuid unassigned) service to > cluster-32f5-m:8020 starting to offer service > {code} > The Datanode then proceeds to use this unresolved address, as it may work if > the DN is configured to use a proxy. Since I'm not using a proxy, it forever > prints out this message: > {code:java} > 2017-12-15 00:13:40,712 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: > Problem connecting to server: cluster-32f5-m:8020 > 2017-12-15 00:13:45,712 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: > Problem connecting to server: cluster-32f5-m:8020 > 2017-12-15 00:13:50,712 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: > Problem connecting to server: cluster-32f5-m:8020 > 2017-12-15 00:13:55,713 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: > Problem connecting to server: cluster-32f5-m:8020 > 2017-12-15 00:14:00,713 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: > Problem connecting to server: cluster-32f5-m:8020 > {code} > Unfortunately, the log doesn't contain the exception that triggered it, but > the culprit is actually in IPC Client: > https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java#L444. > This line was introduced in https://issues.apache.org/jira/browse/HADOOP-487 > to give a clear error message when somebody mispells an address. > However, the fix in HADOOP-7472 doesn't apply here, because that code happens > in Client#getConnection after the Connection is constructed. > My proposed fix (will attach a patch) is to move this exception out of the > constructor and into a place that will trigger HADOOP-7472's logic to > re-resolve addresses. If the DNS failure was temporary, this will allow the > connection to succeed. If not, the connection will fail after ipc client > retries (default 10 seconds worth of retries). > I want to fix this in ipc client rather than just in Datanode startup, as > this fixes temporary DNS issues for all of Hadoop. -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: common-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: common-issues-h...@hadoop.apache.org