Elastic Scaling of a High-Throughput Content-Based Publish/Subscribe Engine

Abstract

Publish/subscribe (pub/sub) infrastructures running as a service on cloud environments offer simplicity and flexibility for composing distributed applications. Provisioning them appropriately is however challenging. The amount of stored subscriptions and incoming publications varies over time, and the computational cost depends on the nature of the applications and in particular on the filtering operation they require (e.g., content-based vs. topic-based, encrypted vs. non-encrypted filtering). The ability to elastically adapt the amount of resources required to sustain given throughput and delay requirements is key to achieving cost-effectiveness for a pub/sub service running in a cloud environment. In this paper, we present the design and evaluation of an elastic contentbased pub/sub system: E-STREAMHUB. Specific contributions of this paper include: (1) a mechanism for dynamic scaling, both out and in, of stateful and stateless pub/sub operators, (2) a local and global elasticity policy enforcer maintaining high system utilization and stable end-to-end latencies, and (3) an evaluation using real-world tick workload from the Frankfurt Stock Exchange and encrypted content-based filtering.

A Novel Approach to Context-Aware Content-Based Middleware

“…This is the major contribution of our research on implementing a proper elastic contentbased publish/subscribe system. It differs from other systems [5] that use pre-state partitioning and simply move slices around. These systems offer no more than application-specific optimized versions of the VM migration provided by all major hypervisors today.…”

“…E-SilboPS is the elastic version of SilboPS. It is the solution for the monitoring problem thanks to its content-based publish/subscribe nature and, unlike other solutions [5], it scales efficiently so as to meet workload demand without overprovisioning or underprovisioning. Additionally, it is based on a newly designed algorithm that shows how to add elasticity in an application with different state constraints: stateless, isolated stateful with external coordination and shared stateful with general coordination.…”

“…On the other hand, if the dynamic state partitioning requirement would dropped, an a priori state partitioning could be applied, as in [5], but in that case no proper elasticity would be present since no real woarkload demand adjustment is present by only system's live migration: a feature that nowadays is offered by all hypervisors because it can be done in an application-agnostic manner.…”

“…Besides, temporary deviations from the standard usage pattern, like load spikes, can be handled without having to restart the system. E-SilboPS is divided into four layers, similar to the engine described in [4,5], and each operator layer can scale in and out independently of the others. Some orchestration between layers is needed, however, to maintain state consistency.…”

“…Esto implica que hay un problema bilateral: cómo puede una aplicación escalar de forma elástica y cómo monitorizar esa aplicación para saber cuándo escalarla horizontalmente. E-SilboPS es la versión elástica de SilboPS y se adapta perfectamente como solución para el problema de monitorización, gracias al paradigma publicador/subscriptor basado en contenido y, a diferencia de otras soluciones [5], permite escalar eficientemente, para cumplir con la carga de trabajo sin sobre-provisionar o sub-provisionar recursos. Además está basado en un algoritmo recientemente diseñado que muestra como añadir elasticidad a una aplicación con distintas restricciones sobre el estado: sin estado, estado aislado con coordinación externa y estado compartido con coordinación general.…”