pkg: Pin to RHCOS 47.198 and quay.io/openshift-release-dev/ocp-release:4.0.0-4

That's the latest RHCOS release:

  $ curl -s https://releases-rhcos.svc.ci.openshift.org/storage/releases/maipo/builds.json | jq '{latest: .builds[0], timestamp}'
  {
    "latest": "47.198",
    "timestamp": "2018-12-08T23:13:22Z"
  }

And Clayton just pushed 4.0.0-alpha.0-2018-12-07-090414 to
quay.io/openshift-release-dev/ocp-release:4.0.0-4.  That's not the
most recent release, but it's the most-recent stable release ;).

Renaming OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE gets us CI testing
of the pinned release despite openshift/release@60007df2 (Use
RELEASE_IMAGE_LATEST for CVO payload, 2018-10-03,
openshift/release#1793).

Author: wking

pkg/asset/ignition/bootstrap/bootstrap.go

@@ -30,7 +30,7 @@ import (
 
 const (
 	rootDir              = "/opt/openshift"
-	defaultReleaseImage  = "registry.svc.ci.openshift.org/openshift/origin-release:v4.0"
+	defaultReleaseImage  = "quay.io/openshift-release-dev/ocp-release:4.0.0-4"
 	bootstrapIgnFilename = "bootstrap.ign"
 )
 
@@ -141,7 +141,7 @@ func (a *Bootstrap) getTemplateData(installConfig *types.InstallConfig, adminKub
 	}
 
 	releaseImage := defaultReleaseImage
-	if ri, ok := os.LookupEnv("OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE"); ok && ri != "" {
+	if ri, ok := os.LookupEnv("_OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE"); ok && ri != "" {
 		logrus.Warn("Found override for ReleaseImage. Please be warned, this is not advised")
 		releaseImage = ri
 	}

pkg/rhcos/builds.go

@@ -33,9 +33,15 @@ type metadata struct {
 }
 
 func fetchLatestMetadata(ctx context.Context, channel string) (metadata, error) {
-	build, err := fetchLatestBuild(ctx, channel)
-	if err != nil {
-		return metadata{}, errors.Wrap(err, "failed to fetch latest build")
+	var build string
+	var err error
+	if channel == DefaultChannel {
+		build = "47.198"
+	} else {
+		build, err = fetchLatestBuild(ctx, channel)
+		if err != nil {
+			return metadata{}, errors.Wrap(err, "failed to fetch latest build")
+		}
 	}
 
 	url := fmt.Sprintf("%s/%s/%s/meta.json", baseURL, channel, build)