func scalingCalculation(tasks *demand.Tasks) (demandChanged bool) {
delta := 0
demandChanged = false
// Work out the ideal scale for all the services
for _, t := range tasks.Tasks {
t.IdealContainers = t.Running + t.Target.Delta(t.Metric.Current())
log.Debugf(" [scale] ideal for %s priority %d would be %d. %d running, %d requested", t.Name, t.Priority, t.IdealContainers, t.Running, t.Requested)
}
available := tasks.CheckCapacity()
log.Debugf(" [scale] available space: %d", available)
// Look for services we could scale down, in reverse priority order
tasks.PrioritySort(true)
for _, t := range tasks.Tasks {
if !t.IsScalable || t.Requested == t.MinContainers {
// Can't scale this service down
continue
}
if t.Running != t.Requested {
// There's a scale operation in progress
log.Debugf(" [scale] %s already scaling: running %d, requested %d", t.Name, t.Running, t.Requested)
continue
}
// For scaling down, delta should be negative
delta = t.ScaleDownCount()
if delta < 0 {
t.Demand = t.Running + delta
demandChanged = true
available += (-delta)
log.Debugf(" [scale] scaling %s down by %d", t.Name, delta)
}
}
// Now look for tasks we need to scale up
tasks.PrioritySort(false)
for p, t := range tasks.Tasks {
if !t.IsScalable {
continue
}
if t.Running != t.Requested {
// There's a scale operation in progress
log.Debugf(" [scale] %s already scaling: running %d, requested %d", t.Name, t.Running, t.Requested)
continue
}
delta = t.ScaleUpCount()
if delta <= 0 {
continue
}
log.Debugf(" [scale] would like to scale up %s by %d - available %d", t.Name, delta, available)
if available < delta {
// If this is a task that fills the remainder, there's no need to exceed capacity
if !t.IsRemainder() {
log.Debugf(" [scale] looking for %d additional capacity by scaling down:", delta-available)
index := len(tasks.Tasks)
freedCapacity := available
for index > p+1 && freedCapacity < delta {
// Kill off lower priority services if we need to
index--
lowerPriorityService := tasks.Tasks[index]
if lowerPriorityService.Priority > t.Priority {
log.Debugf(" [scale] looking for capacity from %s: running %d requested %d demand %d", lowerPriorityService.Name, lowerPriorityService.Running, lowerPriorityService.Requested, lowerPriorityService.Demand)
scaleDownBy := lowerPriorityService.CanScaleDown()
if scaleDownBy > 0 {
if scaleDownBy > (delta - freedCapacity) {
scaleDownBy = delta - freedCapacity
}
lowerPriorityService.Demand = lowerPriorityService.Running - scaleDownBy
demandChanged = true
log.Debugf(" [scale] Service %s priority %d scaling down %d", lowerPriorityService.Name, lowerPriorityService.Priority, -scaleDownBy)
freedCapacity = freedCapacity + scaleDownBy
}
}
}
}
// We might still not have enough capacity and we haven't waited for scale down to complete, so just scale up what's available now
delta = available
log.Debugf(" [scale] Can only scale %s by %d", t.Name, delta)
}
if delta > 0 {
demandChanged = true
available -= delta
if t.Demand >= t.MaxContainers {
log.Errorf(" [scale ] Limiting %s to its configured max %d", t.Name, t.MaxContainers)
t.Demand = t.MaxContainers
} else {
log.Debugf(" [scale] Service %s scaling up %d", t.Name, delta)
t.Demand = t.Running + delta
}
}
}
return demandChanged
}
