[GitHub] [hbase] bharathv commented on a change in pull request #1167: HBASE-18095 Zookeeper-less client connection umbrella

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bharathv commented on a change in pull request #1167: HBASE-18095 Zookeeper-less client connection umbrella
URL: https://github.com/apache/hbase/pull/1167#discussion_r379154192
 
 

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 File path: dev-support/design-docs/HBASE-18095-Zookeeper-less-client-connection-design.adoc
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+= HBASE-18095: Zookeeper-less client connection
+
+
+== Context
+Currently, Zookeeper (ZK) lies in the critical code path of connection init. To set up a connection to a given HBase cluster, client relies on the zookeeper quorum configured in the client hbase-site.xml and attempts to fetch the following information.
+
+* ClusterID
+* Active HMaster server name
+* Meta table region locations
+
+ZK is deemed the source of truth since other processes that maintain the cluster state persist the changes to this data into ZK. So it is an obvious place to look at for clients to fetch the latest cluster state.  However this comes with it’s own set of problems, some of them are below.
+
+* Timeouts and retry logic for ZK clients are managed separately from HBase configuration. This is more administration overhead for end users (example: multiple timeouts are to be configured for different types of RPCs. client->master, client->ZK etc.). This prevents HBase from having a single holistic timeout configuration that applies to any RPCs.
+* If there is any issue with ZK (like connection overload / timeouts), the entire HBase service appears frozen and there is little visibility into it.
+* Exposing zookeeper to all the clients can be risky since it can potentially be abused to DDOS.
+* Embedded ZK client is bundled with hbase client jar as a dependency (with it’s log spew :-]).
 
 Review comment:
   Good point, added.

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