[ZOOKEEPER-851] ZK lets any node to become an observer

• Type: Bug
• Status: Open
• Priority: Critical
• Resolution: Unresolved
• Affects Version/s: 3.3.1
• Component/s: quorum, server
• Assignee: Unassigned
• Reporter: Vishal Kher
• Created: 16/Aug/10 14:12
• Updated: 03/Feb/22 08:50

Description

I had a 3 node cluster running. The zoo.cfg on each contained 3 entries as show below:

tickTime=2000
dataDir=/var/zookeeper
clientPort=2181
initLimit=5
syncLimit=2
server.0=10.150.27.61:2888:3888
server.1=10.150.27.62:2888:3888
server.2=10.150.27.63:2888:3888

I wanted to add another node to the cluster. In fourth node's zoo.cfg, I created another entry for that node and started zk server. The zoo.cfg on the first 3 nodes was left unchanged. The fourth node was able to join the cluster even though the 3 nodes had no idea about the fourth node.

zoo.cfg on fourth node:
tickTime=2000
dataDir=/var/zookeeper
clientPort=2181
initLimit=5
syncLimit=2
server.0=10.150.27.61:2888:3888
server.1=10.150.27.62:2888:3888
server.2=10.150.27.63:2888:3888
server.3=10.17.117.71:2888:3888

It looks like 10.17.117.71 is becoming an observer in this case. I was expecting that the leader will reject 10.17.117.71.

1. telnet 10.17.117.71 2181
   Trying 10.17.117.71...
   Connected to 10.17.117.71.
   Escape character is '^]'.
   stat
   Zookeeper version: 3.3.0--1, built on 04/02/2010 22:40 GMT
   Clients:
   /10.17.117.71:37297[1](queued=0,recved=1,sent=0)

Latency min/avg/max: 0/0/0
Received: 3
Sent: 2
Outstanding: 0
Zxid: 0x200000065
Mode: follower
Node count: 288