version: Output RHEL CoreOS bootimage version

There are a lot of reasons to want to know the RHCOS bootimage version
associated with an installer - the installer pins it today, but doesn't
make the information easy to find particularly in a CI/development
environment.

This is a very small step towards something like:
openshift#1399

cmd/openshift-install/version.go

@@ -1,12 +1,14 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"os"
 
 	"github.com/spf13/cobra"
 
 	"github.com/openshift/installer/pkg/asset/ignition/bootstrap"
+	"github.com/openshift/installer/pkg/rhcos"
 	"github.com/openshift/installer/pkg/version"
 )
 
@@ -28,5 +30,8 @@ func runVersionCmd(cmd *cobra.Command, args []string) error {
 	if image, err := bootstrap.DefaultReleaseImage(); err == nil {
 		fmt.Printf("release image %s\n", image)
 	}
+	if rhcosmeta, err := rhcos.FetchRHCOSBuild(context.TODO()); err == nil {
+		fmt.Printf("RHEL CoreOS bootimage %s\n", rhcosmeta.OSTreeVersion)
+	}
 	return nil
 }

pkg/rhcos/ami.go

@@ -8,7 +8,7 @@ import (
 
 // AMI fetches the HVM AMI ID of the Red Hat Enterprise Linux CoreOS release.
 func AMI(ctx context.Context, region string) (string, error) {
-	meta, err := fetchRHCOSBuild(ctx)
+	meta, err := FetchRHCOSBuild(ctx)
 	if err != nil {
 		return "", errors.Wrap(err, "failed to fetch RHCOS metadata")
 	}

pkg/rhcos/builds.go

@@ -9,7 +9,9 @@ import (
 	"github.com/pkg/errors"
 )
 
-type metadata struct {
+// Metadata is a subset of the `meta.json` generated
+// by https://github.com/coreos/coreos-assembler
+type Metadata struct {
 	AMIs map[string]struct {
 		HVM string `json:"hvm"`
 	} `json:"amis"`
@@ -23,7 +25,8 @@ type metadata struct {
 	OSTreeVersion string `json:"ostree-version"`
 }
 
-func fetchRHCOSBuild(ctx context.Context) (*metadata, error) {
+// FetchRHCOSBuild retrieves the pinned RHEL CoreOS version.
+func FetchRHCOSBuild(ctx context.Context) (*Metadata, error) {
 	file, err := data.Assets.Open("rhcos.json")
 	if err != nil {
 		return nil, err
@@ -35,7 +38,7 @@ func fetchRHCOSBuild(ctx context.Context) (*metadata, error) {
 		return nil, err
 	}
 
-	var meta *metadata
+	var meta *Metadata
 	if err := json.Unmarshal(body, &meta); err != nil {
 		return meta, errors.Wrap(err, "failed to parse RHCOS build metadata")
 	}

pkg/rhcos/qemu.go

@@ -9,7 +9,7 @@ import (
 
 // QEMU fetches the URL of the Red Hat Enterprise Linux CoreOS release.
 func QEMU(ctx context.Context) (string, error) {
-	meta, err := fetchRHCOSBuild(ctx)
+	meta, err := FetchRHCOSBuild(ctx)
 	if err != nil {
 		return "", errors.Wrap(err, "failed to fetch RHCOS metadata")
 	}