Yes, that is helpful. Another big requirement that I forgot to mention is running this on a cloud service provider, like AWS. We already have shared zookeeper setup there with our own client. Ideally, I could inject a custom client for helix to use for operations, where the main differences we would require is a custom top level path (/appname) that is required by our client, and that would handle discovering and connecting to the zookeeper servers.
Is support for AWS and other cloud providers on the roadmap? Also, for the short-term, do you see any complications in us creating an adapter client that helix would use to bridge that gap? Or would it be much more complicated than I am hoping for? Thanks Vu On Wed, Jan 1, 2014 at 8:36 PM, Kanak Biscuitwala <[email protected]>wrote: > Resending since I realized you might not be registered on the user list > yet. By the way, for your specific use case, I would personally lean > towards the CustomCodeRunner along with the CUSTOMIZED IdealState rebalance > mode. Then when nodes enter and exit, you can change the IdealState > yourself and Helix will fire the transitions. This will most easily give > you the policy-driven global view you're looking for. > > --- > > Hi Vu, > > Your understanding is basically correct. The controller will rebalance > each resource in sequence, at most one controller pipeline execution is > going on at any one time, and there is no parallelism within the controller > pipeline (other than batch reading and writing the cluster at the beginning > and end). > > Here are some things that may be of use to know: > > 1. You can plug in your own code to help decide how to rebalance your > cluster in one of two ways: > - Using the CustomCodeRunner on the participant side so that you can > update the IdealState whenever the cluster changes: > https://github.com/apache/incubator-helix/blob/helix-0.6.2-release/helix-core/src/main/java/org/apache/helix/participant/HelixCustomCodeRunner.java?source=c > - Implementing a Rebalancer with USER_DEFINED rebalance mode: > https://github.com/apache/incubator-helix/blob/helix-0.6.2-release/helix-core/src/main/java/org/apache/helix/controller/rebalancer/Rebalancer.java?source=c > > In either case, Helix will still fire transitions according to constraints > and react to node entry/exit. > > 2. Helix supports adding tags to nodes (via InstanceConfig), and > specifying tags in each resource IdealState. Then, a tagged resource will > only be assigned to nodes with the corresponding tag present. > > 3. You can specify max partitions per resource per node in the IdealState > of the resource (this should be 1 in your case) > > 4. You can combine any of the above 3 if that makes sense (e.g. change > node tags whenever a cluster change happens, thus constraining how Helix > will assign everything) > > Is that helpful? > > Kanak > ------------------------------ > Date: Wed, 1 Jan 2014 20:31:56 -0800 > Subject: helix rebalancing for multiple resources > From: [email protected] > To: [email protected] > > > Hi, > We're looking into creating something like a distributed task processing > cluster. We already have existing code for the processing task on a single > host. So that results in stronger restrictions on what we're doing: > - partitioned task A: single partition needs to be assigned to a single > node and a node may have only a single partitioned task > - another set of non-partitioned tasks (e.g. B, C, D) also needs to be > assigned nodes, but it would be most efficient of those tasks are assigned > to separate nodes so any single node has at most 1 task (either partitioned > A, B, C, D, etc.) > > This seems to require a global view of a tasks. However, from the > examples and the Rebalancer code, it appears that the resource > mappings/assignments are independent of each another. Is that correct? If > so, is Apache Helix the right framework for us, given the requirements > above? > > I saw that it might be possible to find the current resource assignment > for other resources during the rebalancing calculation methods, but I was > then concerned about concurrency issues--if the rebalance for task A and > rebalance for B was computed at the same time. > > Thanks for any and all feedback. > > Vu Nguyen >
