1.添加一个函数，定义一个constraint称为multihostConstraint，意思是同一个service的不同副本要落到不同主机上，与其它强制性的constraint不一样，这个是尽量满足的constraint
//检查某个结点是否已经存在属于同一个service的task
func meetMultihosConstraint(nodeInfo *NodeInfo, serviceID string) bool {
for _, task := range nodeInfo.Tasks {
sID = task.ServiceID
if sID == serviceID {
return false
}
}
return true
}
2.修改搜索nodeHeap的函数searchHeapToFindMin，加一个参数serviceID
func (nh *nodeHeap) searchHeapToFindMin(
meetsConstraints func(*NodeInfo) bool,
serviceID string)
(*api.Node, int) {
var bestNode *api.Node //满足multihostConstraint同时task最少的结点
var secondBestNode *api.Node //没有满足multihostConstraint的，只能选一个task最少的结点
minTasks := int(^uint(0) >> 1) // max int
secondMinTasks := minTasks
if nh == nil || len(nh.heap) == 0 {
return bestNode, minTasks
}
// push root to stack for search
stack := []int{0}
for len(stack) != 0 {
// pop an element
idx := stack[len(stack)-1]
stack = stack[0 : len(stack)-1]
heapEntry := &nh.heap[idx]
if len(heapEntry.Tasks) >= minTasks {
continue
}
if meetsConstraints(heapEntry) {
//满足强制性constraint，再检查是否满足multihostConstraint
if meetMultihosConstraint(heapEntry, serviceID) == true {
bestNode = heapEntry.Node
minTasks = len(heapEntry.Tasks)
} else {
if(len(heapEntry.Tasks) < secondMinTasks) {
secondBestNode = heapEntry.Node
secondMinTasks = len(heapEntry.Tasks)
}
}
} else {
// otherwise, push 2 children to stack for further search
if 2*idx+1 < len(nh.heap) {
stack = append(stack, 2*idx+1)
}
if 2*idx+2 < len(nh.heap) {
stack = append(stack, 2*idx+2)
}
}
}
if bestNode == nil {
bestNode = secondBestNode
minTasks = secondMinTasks
}
return bestNode, minTasks
}
修改代码docker/vendor/src/github.com/docker/swarmkit/manager/scheduler/scheduler.go里的scheduleTask函数
// scheduleTask schedules a single task.
func (s *Scheduler) scheduleTask(ctx context.Context, t *api.Task) *api.Task {
s.pipeline.SetTask(t)
//这个函数直接改成searchHeapToFindMin
//s.scanAllNodes是是否扫描全部结点的标志，直接改成false
//n, _ := s.nodeHeap.findMin(s.pipeline.Process, s.scanAllNodes)
n,_ := s.nodeHeap.searchHeapToFindMin(s.pipeline.Process, false, t.ServiceID)
更多Docker相关教程见以下内容：
Docker安装应用(CentOS 6.5_x64)
Ubuntu 14.04安装Docker
在Ubuntu Trusty 14.04 (LTS) (64-bit)安装Docker