Worker upgrading seems to cordon all the nodes at once

[kke]

There should be batching and I'm almost sure there used to be, I think it may have been lost with the dry-run mechanism.

[kke]

Actually it is still there:

func (p *UpgradeWorkers) Run() error {
	if err := p.hosts.Each(p.cordonWorker); err != nil {
		return err
	}

	// Upgrade worker hosts parallelly in 10% chunks
	concurrentUpgrades := int(math.Floor(float64(len(p.hosts)) * 0.10))
	if concurrentUpgrades == 0 {
		concurrentUpgrades = 1
	}

	log.Infof("Upgrading max %d workers in parallel", concurrentUpgrades)
	return p.hosts.BatchedParallelEach(concurrentUpgrades,
		p.start,
		p.cordonWorker,
		p.drainWorker,
		p.upgradeWorker,
		p.uncordonWorker,
		p.finish,
	)
}