Integrate mod_cluster ramp-up mechanism when starting new nodes

In  mod_cluster

Overview

Newly joined nodes can become overloaded, since they initially report 0% load. This has been a problem since inception of the project. The problem is that the initial load stays in effect for performing load-balancing decisions until a new stat interval kicks in. This effect is mitigated by load decay over time, but for the time a new node joins in, it can get overloaded upon startup.

Issue Metadata

Issue

  • WFLY-10769 WFLY-6803 Integrate mod_cluster ramp-up mechanism when starting new nodes

  • EAP7-1087 Integrate mod_cluster ramp-up mechanism when starting new nodes

This feature is supported since mod_cluster version 1.4.0.Final and was part of the original upgrade PR, but was pushed back by QE.

Dev Contacts

QE Contacts

Affected Projects or Components

  • WildFly/EAP

  • mod_cluster

  • Undertow

Other Interested Projects

  • JWS

Requirements

Hard Requirements

  • Nodes are registered with the configured load to gradually ramp them up.

  • The default configuration is that the node is fully loaded (initial-load="0")

Nice-to-Have Requirements

N/A

Non-Requirements

N/A

Test Plan

QE has already pretested the feature.

Community Documentation

The upstream documentation for this is submitted with the implementation PR. Ideally, general documentation for the mod_cluster subsystem will be updated in the near future.