Regarding session mode: ## Session Mode * main() method executed in client
Session mode also supports execution of the main method on Jobmanager with submission through REST API. That's how Flinkk k8s operators like [1] work. It's actually an important capability because it allows for allocation of the cluster resources prior to taking down the previous job during upgrade when the goal is optimization for availability. Thanks, Thomas [1] https://github.com/lyft/flinkk8soperator On Thu, Jan 13, 2022 at 12:32 AM Konstantin Knauf <kna...@apache.org> wrote: > > Hi everyone, > > I would like to discuss and understand if the benefits of having Per-Job > Mode in Apache Flink outweigh its drawbacks. > > > *# Background: Flink's Deployment Modes* > Flink currently has three deployment modes. They differ in the following > dimensions: > * main() method executed on Jobmanager or Client > * dependencies shipped by client or bundled with all nodes > * number of jobs per cluster & relationship between job and cluster > lifecycle* (supported resource providers) > > ## Application Mode > * main() method executed on Jobmanager > * dependencies already need to be available on all nodes > * dedicated cluster for all jobs executed from the same main()-method > (Note: applications with more than one job, currently still significant > limitations like missing high-availability). Technically, a session cluster > dedicated to all jobs submitted from the same main() method. > * supported by standalone, native kubernetes, YARN > > ## Session Mode > * main() method executed in client > * dependencies are distributed from and by the client to all nodes > * cluster is shared by multiple jobs submitted from different clients, > independent lifecycle > * supported by standalone, Native Kubernetes, YARN > > ## Per-Job Mode > * main() method executed in client > * dependencies are distributed from and by the client to all nodes > * dedicated cluster for a single job > * supported by YARN only > > > *# Reasons to Keep** There are use cases where you might need the > combination of a single job per cluster, but main() method execution in the > client. This combination is only supported by per-job mode. > * It currently exists. Existing users will need to migrate to either > session or application mode. > > > *# Reasons to Drop** With Per-Job Mode and Application Mode we have two > modes that for most users probably do the same thing. Specifically, for > those users that don't care where the main() method is executed and want to > submit a single job per cluster. Having two ways to do the same thing is > confusing. > * Per-Job Mode is only supported by YARN anyway. If we keep it, we should > work towards support in Kubernetes and Standalone, too, to reduce special > casing. > * Dropping per-job mode would reduce complexity in the code and allow us to > dedicate more resources to the other two deployment modes. > * I believe with session mode and application mode we have to easily > distinguishable and understandable deployment modes that cover Flink's use > cases: > * session mode: olap-style, interactive jobs/queries, short lived batch > jobs, very small jobs, traditional cluster-centric deployment mode (fits > the "Hadoop world") > * application mode: long-running streaming jobs, large scale & > heterogenous jobs (resource isolation!), application-centric deployment > mode (fits the "Kubernetes world") > > > *# Call to Action* > * Do you use per-job mode? If so, why & would you be able to migrate to one > of the other methods? > * Am I missing any pros/cons? > * Are you in favor of dropping per-job mode midterm? > > Cheers and thank you, > > Konstantin > > -- > > Konstantin Knauf > > https://twitter.com/snntrable > > https://github.com/knaufk
