Heya Geoff, a CouchDB cluster is designed to run in the same data center / with local are networking latencies. A cluster across AWS Availability Zones won’t work as you see. If you want CouchDB’s in both AZs, use regular replication and keep the clusters local to the AZ.
Best Jan -- > On 4. Dec 2017, at 19:46, Geoffrey Cox <[email protected]> wrote: > > Hi, > > I've spent days using trial and error to try and figure out why I am > getting a very high CPU load on only a single node in my cluster. I'm > hoping someone has an idea of what is going on as I'm getting stuck. > > Here's my configuration: > > 1. 2 node cluster: > 1. Each node is located in a different AWS availability zone > 2. Each node is a t2 medium instance (2 CPU cores, 4 GB Mem) > 2. A haproxy server is load balancing traffic to the nodes using round > robin > > The problem: > > 1. After users make changes via PouchDB, a backend runs a number of > routines that use views to calculate notifications. The issue is that on a > single node, the couchjs processes stack up and then start to consume > nearly all the available CPU. This server then becomes the "workhorse" that > always does *all* the heavy duty couchjs processing until I restart this > node. > 2. It is important to note that both nodes have couchjs processes, but > it is only a single node that has the couchjs processes that are using 100% > CPU > 3. I've even resorted to setting `os_process_limit = 10` and this just > results in each couchjs process taking over 10% each! In other words, the > couchjs processes just eat up all the CPU no matter how many couchjs > process there are! > 4. The CPU usage will eventually clear after all the processing is done, > but then as soon as there is more to process the workhorse node will get > bogged down again. > 5. If I restart the workhorse node, the other node then becomes the > workhorse node. This is the only way to get the couchjs processes to "move" > to another node. > 6. The problem is that this design is not scalable as only one node can > be the workhorse node at any given time. Moreover this causes specific > instances to run out of CPU credits. Shouldn't the couchjs processes be > spread out over all my nodes? From what I can tell, if I add more nodes I'm > still going to have the issue where only one of the nodes is getting bogged > down. Is it possible that the problem is that I have 2 nodes and really I > need at least 3 nodes? (I know a 2-node cluster is not very typical) > > > Things I've checked: > > 1. Ensured that the load balancing is working, i.e. haproxy is indeed > distributing traffic accordingly > 2. I've tried setting `os_process_limit = 10` and `os_process_soft_limit > = 5` to see if I could force a more conservative usage of couchjs > processes, but instead the couchjs processes just consume all the CPU load. > 3. I've tried simulating the issue locally with VMs and I cannot > duplicate any such load. My guess is that this is because the nodes are > located on the same box so hop distance between nodes is very small and > this somehow keeps the CPU usage to a minimum > 4. I've tried isolating the issue by creating short code snippets that > intentionally try to spawn a lot of couchjs processes and they are spawned > but don't consume 100% CPU > 5. I've tried rolling back from CouchDB 2.1.1 to CouchDB 2.0 and this > doesn't seem to change anything > 6. The only error entries in my CouchDB logs are like the following and > I don't believe they are related to my issue: > 1. > > [error] 2017-12-04T18:13:38.728970Z [email protected] <0.13974.79> > 4b0b21c664 rexi_server: from: [email protected](<0.20638.79>) mfa: > fabric_rpc:open_shard/2 throw:{forbidden,<<"You are not allowed to access > this db.">>} > > [{couch_db,open,2,[{file,"src/couch_db.erl"},{line,185}]},{fabric_rpc,open_shard,2,[{file,"src/fabric_rpc.erl"},{line,267}]},{rexi_server,init_p,3,[{file,"src/rexi_server.erl"},{line,139}]}] > > Does CouchDB have some logic built in that spawns a number of couchjs > processes on a "primary" node? Will future view processing then always be > routed to this "primary" node? > > Is there a way to better distribute these heavy duty couchjs processes? Is > it possible to limit their CPU consumption? (I'm hesitant to start down the > path of using something like cpulimit as I think there is a root problem > that needs to be addressed) > > I'm running out of ideas and hope that someone has some notion of what is > causing this bizarre load or if there is a bug in CouchDB. > > Thank you for any help you can provide! > > Geoff -- Professional Support for Apache CouchDB: https://neighbourhood.ie/couchdb-support/
