virtigo/start.go

package main

// validates the droplet information
// finds a hypervisor
// attempts to start the virtual machine

import (
	"errors"
	"fmt"
	"math/rand"
	"time"

	pb "go.wit.com/lib/protobuf/virtbuf"
)

func isClusterStable() (string, error) {
	// how long has the cluster been stable?
	// wait until it is stable. use this to throttle droplet starts
	dur := time.Since(me.unstable)
	good := fmt.Sprintln("trying to start droplet here. grid stable for: ", pb.FormatDuration(dur))
	if dur < me.unstableTimeout {
		tmp := pb.FormatDuration(me.unstableTimeout)
		err := "grid is still too unstable (unstable timeout = " + tmp + ")\n"
		return good + err, errors.New(err)
	}
	return good, nil
}

// for now, because sometimes this should write to stdout and
// sometimes to http socket, it returns a string
func Start(name string) (string, error) {
	var result string

	if s, err := isClusterStable(); err != nil {
		result += s
		return result, err
	}

	// lookup the droplet by name
	d := me.cluster.FindDropletByName(name)
	if d == nil {
		result = "can't start unknown droplet: " + name
		return result, errors.New(result)
	}

	// validate the droplet
	if err := ValidateDroplet(d); err != nil {
		result = "ValidateDroplet() failed droplet " + d.Hostname
		return result, err
	}

	// is the droplet already on?
	if d.Current.State == pb.DropletState_ON {
		result = "EVENT start droplet " + d.Hostname + " is already ON"
		return result, errors.New(result)
	}

	// make the list of hypervisors that are active and can start new droplets
	var pool []*HyperT
	for _, h := range me.hypers {
		// this droplet is set to use this and only this hypervisor
		if d.ForceHypervisor == h.pb.Hostname {
			ok, b := h.start(d)
			if ok {
				return result + b, nil
			}
			return result + b, errors.New("start " + name + " on hypervisor " + h.pb.Hostname)
		}

		// skip hypervisors marked inactive
		if h.pb.Active != true {
			result += fmt.Sprintln("hypervisor is inactive:", name, "for", h.pb.Hostname, h.pb.Active)
			continue
		}

		// the config file says this droplet should run on this hypervisor
		// attempt to start the droplet here. use this even if the hypervisor is inactive?
		if d.PreferredHypervisor == h.pb.Hostname {
			ok, b := h.start(d)
			if ok {
				return result + b, nil
			}
			return result + b, errors.New("start " + name + " on hypervisor " + h.pb.Hostname)
		}

		result += fmt.Sprintln("hypervisor ready:", name, "for", h.pb.Hostname, h.pb.Active)
		pool = append(pool, h)
	}

	// left here as an example of how to actually do random numbers
	// it's complete mathematical chaos. Randomness is simple when
	// human interaction occurs -- which is exactly what happens most
	// of the time. most random shit is bullshit. all you really need
	// is exactly this to make sure the random functions work as they
	// should. Probably, just use this everywhere in all cases. --jcarr
	rand.Seed(time.Now().UnixNano())
	a := 0
	b := len(pool)
	n := a + rand.Intn(b-a)
	result += fmt.Sprintln("pool has", len(pool), "members", "rand =", n)
	h := pool[n]

	ok, output := h.start(d)
	if ok {
		return result + output, nil
	}
	return result + output, errors.New("start " + name + " on hypervisor " + h.pb.Hostname)
}