[SOLR-8868] SolrCloud: if zookeeper loses and then regains a quorum, Solr nodes and SolrJ Client do not recover and need to be restarted

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Done
• Affects Version/s: 5.3.1
• Component/s: SolrCloud, SolrJ
• Assignee: Unassigned
• Reporter: Frank J Kelly
• Created: 17/Mar/16 20:09
• Updated: 03/Apr/20 22:49
• Resolved: 03/Apr/20 22:49

Description

Tried mailing list on 3/15 and 3/16 to no avail. Hopefully I gave enough details.

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Just wondering if my observation of SolrCloud behavior after ZooKeeper loses a quorum is normal or to-be-expected

Version of Solr: 5.3.1
Version of ZooKeeper: 3.4.7
Using SolrCloud with external ZooKeeper
Deployed on AWS

Our Solr cluster has 3 nodes (m3.large)

Our Zookeeper ensemble consists of three nodes (t2.small) with the same config using DNS names e.g.

$ more ../conf/zoo.cfg
tickTime=2000
dataDir=/var/zookeeper
dataLogDir=/var/log/zookeeper
clientPort=2181
initLimit=10
syncLimit=5
standaloneEnabled=false
server.1=zookeeper1.qa.eu-west-1.mysearch.com:2888:3888
server.2=zookeeper2.qa.eu-west-1.mysearch.com:2888:3888
server.3=zookeeper3.qa.eu-west-1.mysearch.com:2888:3888

If we terminate one of the zookeeper nodes we get a ZK election (and I think) a quorum is maintained.
Operation continues OK and we detect the terminated instance and relaunch a new ZK node which comes up fine

If we terminate two of the ZK nodes we lose a quorum and then we observe the following

1.1) Admin UI shows an error that it is unable to contact ZooKeeper “Could not connect to ZooKeeper"

1.2) SolrJ returns the following

org.apache.solr.common.SolrException: Could not load collection from ZK:qa_eu-west-1_public_index
at org.apache.solr.common.cloud.ZkStateReader.getCollectionLive(ZkStateReader.java:850)
at org.apache.solr.common.cloud.ZkStateReader$7.get(ZkStateReader.java:515)
at org.apache.solr.client.solrj.impl.CloudSolrClient.getDocCollection(CloudSolrClient.java:1205)
at org.apache.solr.client.solrj.impl.CloudSolrClient.requestWithRetryOnStaleState(CloudSolrClient.java:837)
at org.apache.solr.client.solrj.impl.CloudSolrClient.request(CloudSolrClient.java:805)
at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:135)
at org.apache.solr.client.solrj.SolrClient.add(SolrClient.java:107)
at org.apache.solr.client.solrj.SolrClient.add(SolrClient.java:72)
at org.apache.solr.client.solrj.SolrClient.add(SolrClient.java:86)
at com.here.scbe.search.solr.SolrFacadeImpl.addToSearchIndex(SolrFacadeImpl.java:112)
Caused by: org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /collections/qa_eu-west-1_public_index/state.json
at org.apache.zookeeper.KeeperException.create(KeeperException.java:99)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.solr.common.cloud.SolrZkClient$7.execute(SolrZkClient.java:345)
at org.apache.solr.common.cloud.SolrZkClient$7.execute(SolrZkClient.java:342)
at org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:61)
at org.apache.solr.common.cloud.SolrZkClient.getData(SolrZkClient.java:342)
at org.apache.solr.common.cloud.ZkStateReader.getCollectionLive(ZkStateReader.java:841)
... 24 more

This makes sense based on our understanding.
When our AutoScale groups launch two new ZooKeeper nodes, initialize them, fix the DNS etc. we regain a quorum but at this point

2.1) Admin UI shows the shards as “GONE” (all greyed out)

2.2) SolrJ returns the same error even though the ZooKeeper DNS names are now bound to new IP addresses

So at this point I restart the Solr nodes. At this point then

3.1) Admin UI shows the collections as OK (all shards are green) – yeah the nodes are back!

3.2) SolrJ Client still shows the same error – namely

org.apache.solr.common.SolrException: Could not load collection from ZK:qa_eu-west-1_here_account
at org.apache.solr.common.cloud.ZkStateReader.getCollectionLive(ZkStateReader.java:850)
at org.apache.solr.common.cloud.ZkStateReader$7.get(ZkStateReader.java:515)
at org.apache.solr.client.solrj.impl.CloudSolrClient.getDocCollection(CloudSolrClient.java:1205)
at org.apache.solr.client.solrj.impl.CloudSolrClient.requestWithRetryOnStaleState(CloudSolrClient.java:837)
at org.apache.solr.client.solrj.impl.CloudSolrClient.request(CloudSolrClient.java:805)
at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:135)
at org.apache.solr.client.solrj.SolrClient.deleteById(SolrClient.java:825)
at org.apache.solr.client.solrj.SolrClient.deleteById(SolrClient.java:788)
at org.apache.solr.client.solrj.SolrClient.deleteById(SolrClient.java:803)
at com.here.scbe.search.solr.SolrFacadeImpl.deleteById(SolrFacadeImpl.java:257)
.
.
Caused by: org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss for /collections/qa_eu-west-1_here_account/state.json
at org.apache.zookeeper.KeeperException.create(KeeperException.java:99)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.solr.common.cloud.SolrZkClient$7.execute(SolrZkClient.java:345)
at org.apache.solr.common.cloud.SolrZkClient$7.execute(SolrZkClient.java:342)
at org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:61)
at org.apache.solr.common.cloud.SolrZkClient.getData(SolrZkClient.java:342)
at org.apache.solr.common.cloud.ZkStateReader.getCollectionLive(ZkStateReader.java:841)

Is this behavior (lack of self-healing) a known and expected behavior?

If this is expected behavior then likely this should be recast as an Improvement request?

Is this the same or similar behavior as documented here https://issues.apache.org/jira/browse/SOLR-5129

p.s. I can add Solr log files if they will help

Issue Links

• is fixed by: ZOOKEEPER-2184 Zookeeper Client should re-resolve hosts when connection attempts fail
• is related to: SOLR-12727 Upgrade ZooKeeper dependency to 3.4.13