Add RHCOSBaseURI to templating for bootstrap files

This allows us to template in the baseURI from data/data/rhcos.json
when needed for boostrap files (the baremetal platform requires this
to download the appropriate image to provision the masters)

pkg/asset/ignition/bootstrap/bootstrap.go

@@ -26,6 +26,7 @@ import (
 	"github.com/openshift-metalkube/kni-installer/pkg/asset/machines"
 	"github.com/openshift-metalkube/kni-installer/pkg/asset/manifests"
 	"github.com/openshift-metalkube/kni-installer/pkg/asset/tls"
+	"github.com/openshift-metalkube/kni-installer/pkg/rhcos"
 	"github.com/openshift-metalkube/kni-installer/pkg/types"
 )
 
@@ -42,6 +43,7 @@ type bootstrapTemplateData struct {
 	PullSecret   string
 	ReleaseImage string
 	Proxy        *configv1.ProxyStatus
+	RHCOSBaseURI string
 }
 
 // Bootstrap is an asset that generates the ignition config for bootstrap nodes.
@@ -208,11 +210,24 @@ func (a *Bootstrap) getTemplateData(installConfig *types.InstallConfig, proxy *c
 		logrus.Debugf("Using internal constant for release image %s", releaseImage)
 	}
 
+	var rhcosImageBaseURI string
+	if ri, ok := os.LookupEnv("OPENSHIFT_INSTALL_IMAGE_BASE_URI_OVERRIDE"); ok && ri != "" {
+		logrus.Warn("Found override for rhcosImageBaseURI. Please be warned, this is not advised")
+		rhcosImageBaseURI = ri
+	} else {
+		rhcosImageBaseURI, err := rhcos.BaseURI()
+		if err != nil {
+			return nil, err
+		}
+		logrus.Debugf("Using internal constant for release image base URI %s", rhcosImageBaseURI)
+	}
+
 	return &bootstrapTemplateData{
 		PullSecret:   installConfig.PullSecret,
 		ReleaseImage: releaseImage,
 		EtcdCluster:  strings.Join(etcdEndpoints, ","),
 		Proxy:        &proxy.Status,
+		RHCOSBaseURI: rhcosImageBaseURI,
 	}, nil
 }
 

pkg/rhcos/baseuri.go

@@ -0,0 +1,23 @@
+package rhcos
+
+import (
+	"context"
+	"net/url"
+
+	"github.com/pkg/errors"
+)
+
+// BaseURI fetches the BaseURI where images can be downloaded from
+func BaseURI() (string, error) {
+	meta, err := fetchRHCOSBuild(context.TODO())
+	if err != nil {
+		return "", errors.Wrap(err, "failed to fetch RHCOS metadata")
+	}
+
+	base, err := url.Parse(meta.BaseURI)
+	if err != nil {
+		return "", err
+	}
+
+	return base.String(), nil
+}