github.com/mattyw/juju@v0.0.0-20140610034352-732aecd63861/environs/instances/image.go

// Copyright 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package instances

import (
	"fmt"
	"sort"

	"github.com/juju/juju/constraints"
	"github.com/juju/juju/environs/imagemetadata"
	"github.com/juju/juju/juju/arch"
)

// InstanceConstraint constrains the possible instances that may be
// chosen by the environment provider.
type InstanceConstraint struct {
	Region      string
	Series      string
	Arches      []string
	Constraints constraints.Value
	// Optional filtering criteria not supported by all providers. These attributes are not specified
	// by the user as a constraint but rather passed in by the provider implementation to restrict the
	// choice of available images.
	Storage *string
}

// String returns a human readable form of this InstanceConstaint.
func (ic *InstanceConstraint) String() string {
	storage := "none"
	if ic.Storage != nil {
		storage = *ic.Storage
	}
	return fmt.Sprintf(
		"{region: %s, series: %s, arches: %s, constraints: %s, storage: %s}",
		ic.Region,
		ic.Series,
		ic.Arches,
		ic.Constraints,
		storage,
	)
}

// InstanceSpec holds an instance type name and the chosen image info.
type InstanceSpec struct {
	InstanceType InstanceType
	Image        Image
	// order is used to sort InstanceSpec based on the input InstanceTypes.
	order int
}

// FindInstanceSpec returns an InstanceSpec satisfying the supplied InstanceConstraint.
// possibleImages contains a list of images matching the InstanceConstraint.
// allInstanceTypes provides information on every known available instance type (name, memory, cpu cores etc) on
// which instances can be run. The InstanceConstraint is used to filter allInstanceTypes and then a suitable image
// compatible with the matching instance types is returned.
func FindInstanceSpec(possibleImages []Image, ic *InstanceConstraint, allInstanceTypes []InstanceType) (*InstanceSpec, error) {
	if len(possibleImages) == 0 {
		return nil, fmt.Errorf("no %q images in %s with arches %s",
			ic.Series, ic.Region, ic.Arches)
	}

	var matchingTypes []InstanceType
	if ic.Constraints.HasInstanceType() {
		for _, itype := range allInstanceTypes {
			if itype.Name == *ic.Constraints.InstanceType {
				matchingTypes = append(matchingTypes, itype)
				break
			}
		}
		if len(matchingTypes) == 0 {
			return nil, fmt.Errorf("invalid instance type %q", *ic.Constraints.InstanceType)
		}
	} else {
		var err error
		matchingTypes, err = getMatchingInstanceTypes(ic, allInstanceTypes)
		if err != nil {
			return nil, err
		}
	}
	if len(matchingTypes) == 0 {
		return nil, fmt.Errorf("no instance types found matching constraint: %s", ic)
	}

	specs := []*InstanceSpec{}
	for _, itype := range matchingTypes {
		for _, image := range possibleImages {
			if image.match(itype) {
				specs = append(specs, &InstanceSpec{
					InstanceType: itype,
					Image:        image,
					order:        len(specs),
				})
			}
		}
	}
	if len(specs) > 0 {
		sort.Sort(byArch(specs))
		return specs[0], nil
	}

	names := make([]string, len(matchingTypes))
	for i, itype := range matchingTypes {
		names[i] = itype.Name
	}
	return nil, fmt.Errorf("no %q images in %s matching instance types %v", ic.Series, ic.Region, names)
}

// byArch sorts InstanceSpecs first by descending word-size, then
// alphabetically by name, and choose the first spec in the sequence.
type byArch []*InstanceSpec

func (a byArch) Len() int {
	return len(a)
}

func (a byArch) Less(i, j int) bool {
	iArchName := a[i].Image.Arch
	jArchName := a[j].Image.Arch
	iArch := arch.Info[iArchName]
	jArch := arch.Info[jArchName]
	// Wider word-size first.
	switch {
	case iArch.WordSize > jArch.WordSize:
		return true
	case iArch.WordSize < jArch.WordSize:
		return false
	}
	// Alphabetically by arch name.
	switch {
	case iArchName < jArchName:
		return true
	case iArchName > jArchName:
		return false
	}
	// If word-size and name the same, keep stable.
	return a[i].order < a[j].order
}

func (a byArch) Swap(i, j int) {
	a[i], a[j] = a[j], a[i]
}

// Image holds the attributes that vary amongst relevant images for
// a given series in a given region.
type Image struct {
	Id   string
	Arch string
	// The type of virtualisation supported by this image.
	VirtType string
}

// match returns true if the image can run on the supplied instance type.
func (image Image) match(itype InstanceType) bool {
	// The virtualisation type is optional.
	if itype.VirtType != nil && image.VirtType != *itype.VirtType {
		return false
	}
	for _, arch := range itype.Arches {
		if arch == image.Arch {
			return true
		}
	}
	return false
}

// ImageMetadataToImages converts an array of ImageMetadata pointers (as
// returned by imagemetadata.Fetch) to an array of Image objects (as required
// by instances.FindInstanceSpec).
func ImageMetadataToImages(inputs []*imagemetadata.ImageMetadata) []Image {
	result := make([]Image, len(inputs))
	for index, input := range inputs {
		result[index] = Image{
			Id:       input.Id,
			VirtType: input.VirtType,
			Arch:     input.Arch,
		}
	}
	return result
}