Yongjun Zhang; Workers Software program Engineer | William Tom; Workers Software program Engineer | Sandeep Kumar; Software program Engineer | Hengzhe Guo; Software program Engineer |
Monarch, Pinterest’s Batch Processing Platform, was initially designed to assist Pinterest’s ever-growing variety of Apache Spark and MapReduce workloads at scale. Throughout Monarch’s inception in 2016, probably the most dominant batch processing know-how round to construct the platform was Apache Hadoop YARN. Now, eight years later, we have now made the choice to maneuver off of Apache Hadoop and onto our subsequent technology Kubernetes (K8s) primarily based platform. These are a few of the key points we purpose to handle:
- Utility isolation with containerization: In Apache Hadoop 2.10, YARN purposes share the identical widespread surroundings with out container isolation. This typically results in arduous to debug dependency conflicts between purposes.
- GPU assist: Node labeling assist was added to Apache Hadoop YARN’s Capability Scheduler (YARN-2496) and never Honest Scheduler (YARN-2497), however at Pinterest we’re closely invested in Honest Scheduler. Upgrading to a more moderen Apache Hadoop model with node labeling assist in Honest Scheduler or migrating to Capability Scheduler would require large engineering effort.
- Hadoop improve effort: In 2020, we upgraded from Apache Hadoop 2.7 to 2.10. This minor model improve course of took roughly one 12 months. A serious model improve to three.x will take us considerably extra time.
- Hadoop group assist: The trade as an entire has been shifting to K8s and Apache Hadoop is basically in upkeep mode.
Over the previous few years, we’ve noticed widespread trade adoption of K8s to handle these challenges. After a prolonged inside proof of idea and analysis we made the choice to construct out our subsequent technology K8s-based platform: Moka (Monarch on K8s).
On this weblog, we’ll be protecting the challenges and corresponding options that allow us emigrate hundreds of Spark purposes from Monarch to Moka whereas sustaining useful resource effectivity and a top quality of service. You possibly can take a look at our earlier weblog, which describes how Monarch sources are managed effectively to attain value saving whereas making certain job stability. On the time of penning this weblog, we have now migrated half of the Spark workload operating on Monarch to Moka. The remaining MapReduce jobs operating on Monarch are actively being migrated to Spark as a part of a separate initiative to deprecate MapReduce inside Pinterest.
Our objective with Moka useful resource administration was to retain the constructive properties of Monarch’s useful resource administration and enhance upon its shortcomings.
First, let’s cowl the issues that labored nicely on Monarch that we needed to carry over to Moka:
- Associating every workflow with its proprietor’s group and mission
- Classifying all workflows into three tiers: tier 1 (highest precedence), tier 2, and tier 3, and defining the runtime SLO for every workflow
- Utilizing hierarchical org-base-queue (OBQ) within the format of
root.<group>.<mission>.<tier> for useful resource allocation and workload scheduling - Monitoring per-application runtime information, together with the applying’s begin and finish time, reminiscence and vCore utilization, and so on.
- Environment friendly tier-based useful resource allocation algorithms that robotically regulate OBQs primarily based on the historic useful resource utilization of the workflows assigned to the queues
- Providers that may route workloads from one cluster to a different, which we name cross-cluster-routing (CCR), to their corresponding OBQs
- Onboarding queues with reserved sources to onboard new workloads
- Periodic useful resource allocation processes handle OBQs from the useful resource utilization information collected throughout the onboarding queue runs
- Dashboards to observe useful resource utilization and workflow runtime SLO efficiency
Step one to programmatically migrating workloads from Monarch to Moka at scale is useful resource allocation. Many of the gadgets listed above could be re-used as-is or simply prolonged to assist Moka. Nevertheless, there are a number of extra gadgets that we would want to assist useful resource allocation on Moka:
- A scheduler that’s application-aware, permits managing cluster sources as hierarchical queues, and helps preemption
- A pipeline to export useful resource utilization data for all purposes run on Moka and ingestion pipelines to generate perception tables
- A useful resource allocation job that makes use of the insights tables to generate the OBQ useful resource allocation
- An orchestration layer that is ready to route workloads to their goal clusters and OBQs
Now let’s go into element on how we solved these 4 lacking items.
The default K8s scheduler is a “jack of all trades, grasp of none” resolution that isn’t significantly adept at scheduling batch processing workloads. For our useful resource scheduling wants, we wanted a scheduler that helps hierarchical queues and is ready to schedule on a per-application and per-user foundation as an alternative of per-pod foundation.
Apache YuniKorn is designed by a gaggle of engineers with deep expertise engaged on Apache Hadoop YARN and K8s. Apache YuniKorn not solely acknowledges customers, purposes, and queues, but in addition contains many different elements, comparable to ordering, priorities, and preemption when making scheduling choices.
On condition that Apache YuniKorn has probably the most attributes we’d like, we determined to make use of it in Moka.
As talked about earlier, utility useful resource utilization historical past is crucial for the way we do useful resource allocation. At a excessive degree, we use the historic utilization of a queue as a baseline to estimate how a lot must be allotted going ahead in every iteration of the allocation course of. Nevertheless, after we made the choice to first undertake Apache YuniKorn it was lacking this very important function. Apache YuniKorn was fully stateless and solely tracked instantaneous useful resource utilization throughout the cluster.
We wanted an answer that will have the ability to reliably observe useful resource consumption of all pods belonging to an utility and was fault tolerant. For this, we labored carefully with the Apache YuniKorn group so as to add assist for logging useful resource utilization data for completed purposes (see YUNIKORN-1385 for extra data). This function aggregates pod useful resource utilization per utility and experiences a remaining useful resource utilization abstract upon utility completion.
This abstract is logged to Apache YuniKorn’s stdout the place we use Fluent Bit to filter out the app abstract logs and write them to S3.
By design, the Apache YuniKorn utility abstract incorporates comparable data as YARN’s utility abstract produced by YARN ResourceManager (see extra particulars on this document) in order that it might match seamlessly into current customers of YARN utility summaries.
Along with utility useful resource utilization data, the next mapping data is robotically ingested into the perception tables:
- Workflow to mission, tier, SLO
- Venture to proprietor
- Proprietor to firm group
- Workflow job to purposes
This data is used for associating workloads with their goal queue and estimating the queue’s future useful resource necessities.
Determine 1 reveals the knowledge ingestion and useful resource allocation stream.
To study extra concerning the useful resource allocation algorithm, see our earlier weblog put up: Environment friendly Useful resource Administration at Pinterest’s Batch Processing Platform.
Our algorithm prioritizes useful resource allocation to tier 1 and tier 2 queues as much as a specified percentile threshold of the queue’s required sources.
One draw back to this method is that it typically requires a number of iterations of useful resource allocation to converge to a secure one, the place every iteration requires some handbook tuning of parameters.
As a part of the Moka migration, we designed and carried out a model new algorithm that leverages Constraint Programming Using CP-SAT from the OR-Tools open supply suite for optimization. This software generates a mannequin by developing a set of constraints primarily based on the utilization/capability ratio hole between excessive tier (tier 1 and a couple of) and low tier (tier 3) useful resource requests. This new useful resource allocation algorithm runs sooner and extra reliably with out human intervention.
Our job submission layer, Archer, is answerable for dealing with all job submissions to Moka. Archer gives flexibility on the platform degree to investigate, modify and route jobs at submission time. This contains routing jobs to particular Moka clusters and queues.
Determine 2 reveals how we do useful resource allocation with CCR for choose jobs and the deployment course of. The useful resource allocation change made at git repo is robotically submitted to Archer, and Archer talks to k8s to deploy the modified useful resource allocation config map, after which route jobs at runtime primarily based on the CCR guidelines arrange within the Archer Routing DB.
We plan to cowl Archer and Moka in future weblog posts.
Along with YUNIKORN-1385, listed here are another options and fixes we contributed again to the Apache YuniKorn group.
- YUNIKORN-790: Provides assist for maxApplications to restrict the variety of purposes that may run concurrently in any queue
- YUNIKORN-2030: Fixes a bug when checking headroom which causes Apache YuniKorn to stall
- YUNIKORN-970 Add queue metrics with queue names as tags to make queue metrics simpler to trace and examine
- YUNIKORN-1948 Introduce a command to validate the content material of a given queue config file
Apache YuniKorn continues to be a comparatively younger open supply mission, and we’re persevering with to work with the group collectively to complement its performance and enhance its reliability and effectivity.
As soon as we began to onboard actual manufacturing workloads to Moka, we prolonged our current Workflow SLO Efficiency Dashboards for Monarch to incorporate the day by day runtime outcomes of apps operating on Moka. Our objective is to make sure a minimum of 90% of tier 1 workflows meet their SLO a minimum of 90% of time.
Regardless of having made nice progress constructing out the Moka platform and migrating jobs from our legacy platform there are nonetheless many enhancements we have now deliberate. To present you a teaser of what’s to come back:
We’re within the technique of designing a stateful service that is ready to leverage YUNIKORN-1628 and YUNIKORN-2115 which introduce occasion streaming assist.
As well as, we’re engaged on a full-featured useful resource administration console to handle the platform sources. This console will allow platform directors to observe cluster and queue useful resource utilization in actual time and permits customized load balancing between clusters.
Initially, because of the Apache YuniKorn group for his or her help and collaboration after we had been evaluating Apache YuniKorn and for working with us to submit patches we made internally again to the open supply mission.
Subsequent, because of our good teammates, Rainie Li, Hengzhe Guo, Soam Acharya, Bogdan Pisica, Aria Wang from the Batch Processing Platform and Knowledge Processing Infra groups for his or her work on Moka. Thanks Ang Zhang, Jooseong Kim, Chen Qin, Soam Acharya, Chunyan Wang et al for his or her assist and insights whereas we had been engaged on the mission.
Final however not least, thanks to the Workflow Platform workforce and the entire consumer groups of our platform for his or her suggestions.
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