Which couchbase node will serve request?

Question

I am having NodeJS service which talks to couchbase cluster to fetch the data. The couchbase cluster has 4 nodes(running on ip1, ip2, ip3, ip4) and service also is running on same 4 servers. On all the NodeJS services my connection string looks like this:

couchbase://ip1,ip2,ip3,ip4

but whenever I try to fetch some document from bucket X, console shows node on ip4 is doing that operation. No matter which NodeJS application is making request the same ip4 is serving all the request.

I want each NodeJS server to use their couchbase node so that RAM and CPU consumption on all the servers are equal so I changed the order of IPs in connection string but every time request is being served by same ip4.

I created another bucket and put my data in it and try to fetch it but again it went to same ip4. Can someone explain why is this happening and can it cause high load on one of the node?

Answer 1

What do you mean by "I want each NodeJS server to use their couchbase node"? In Couchbase, part of the active dataset is on each node in the cluster. The sharding is automatic. When you have a cluster, the 1024 active vBuckets (shards) for each Bucket are spread out across all the nodes of the cluster. So with your 4 nodes, there will be 256 vBuckets on each node. Given the consistent hashing algorithm used by the Couchbase SDK, it will be able to tell from the key which vBucket that object goes into and combined with the cluster map it got from the cluster, know which node that vBucket lives in the cluster. So an app will be getting data from each of the nodes in the cluster if you have it configured correctly as the data is evenly spread out.

On the files system there will be as part of the Couchbase install a CLI tool call vbuckettool that takes an objectID and clustermap as arguments. All it does is the consistent hashing algorithm + the clustermap. So you can actually predict where an object will go even if it does not exist yet.

On a different note, best practice in production is to not run your application on the same nodes as Couchbase. It really is supposed to be separate to get the most out of its shared nothing architecture among other reasons.