在2个节点的集群上运行zookeeper

Question

I am currently working on trying to use zookeeper in a two node cluster. I have my own cluster formation algorithm running on the nodes based on configuration. We only need Zookeeper's distributed DB functionality.

1. Is it possible to use Zookeeper in a two node cluster ? Do you know of any solutions where this has been done ?
2. Can we still retain the zookeepers DB functionality without forming a quorum ?

Note: Fault tolerance is not the main concern in this project. If one of the nodes go down we have enough code logic to run without the zookeeper service. We use the zookeeper to share data when both the nodes are alive.

Would greatly appreciate any help.

Answer 1

Zookeeper is a coordination system which is basically used to coordinate among nodes. When writes are occurred to such a distributed system, in ordered to coordinate and agree upon values which are being stored, all the writes are gone through master (aka leader) . Reads can occur through any node. Zookeeper requires a master/leader to be elected per a quorum in order to serve write requests consistently. Zookeeper make use of the ZAB protocol as the consensus algorithm.

1. In order to elect a leader, a quorum should ideally have an odd number of nodes (Otherwise, a node will not be able to win majority and become the leader). In your case, with two nodes, zookeeper will not possibly be able to elect a leader for a long time since both nodes will be candidates and wait for the other node to vote for it. Even though they elect a leader, your ensemble will not work properly in network patitioning situations.
2. As I said, zookeeper is not a distributed storage. If you need to use it in a distributed manner (more than one node), it need to form a quorum.

As I see, what you need is a distributed database. Not a distributed coordination system.