Split dockerfile generation in multiple steps

Signed-off-by: Dimitris Karakasilis <dimitris@karakasilis.me>

Dockerfile

@@ -1,26 +1,19 @@
-ARG GO_VERSION=1.20-alpine3.18
-FROM golang:$GO_VERSION AS builder
 
-WORKDIR /build
-COPY . .
+FROM ubuntu:latest as base
+FROM busybox as builder
 
-ENV CGO_ENABLED=0
-RUN go mod download
-# Set arg/env after go mod download, otherwise we invalidate the cached layers due to the commit changing easily
-ARG ENKI_VERSION
-ARG ENKI_COMMIT
-ENV ENKI_VERSION=${ENKI_VERSION}
-ENV ENKI_COMMIT=${ENKI_COMMIT}
-RUN go build \
-    -ldflags "-w -s \
-    -X github.com/kairos-io/enki/internal/version.version=$ENKI_VERSION \
-    -X github.com/kairos-io/enki/internal/version.gitCommit=$ENKI_COMMIT" \
-    -o /enki
+COPY --from=base . /rootfs
 
-FROM gcr.io/kaniko-project/executor:latest
+FROM rootfs
+# Additional os specific things
 
-COPY --from=builder /enki /enki
+RUN echo "nameserver 8.8.8.8" > /rootfs/etc/resolv.conf
+RUN cat /rootfs/etc/resolv.conf
 
-ENTRYPOINT ["/enki"]
+FROM scratch as rootfs
+
+COPY --from=builder /rootfs/ .
+
+FROM rootfs
+# Additional os specific things
 
-CMD ["convert"]

cmd/dockerfile.go

@@ -16,9 +16,9 @@ func NewDockerfileCmd() *cobra.Command {
 		Long: "Create a dockerfile that builds a Kairos image from the provided one\n\n" +
 			"The base image can be specified either as a directory where the image has been extracted or as an image uri.\n" +
 			"This is best effort. Enki will try to detect the distribution and add the necessary bits to convert it to a Kairos image",
-		Args: cobra.ExactArgs(3),
 		PreRunE: func(cmd *cobra.Command, args []string) error {
-			return CheckRoot() // TODO: Do we need root?
+			//return CheckRoot() // TODO: Do we need root?
+			return nil
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {
 			// Set this after parsing of the flags, so it fails on parsing and prints usage properly

pkg/action/converter.go

@@ -55,9 +55,10 @@ func NewConverterAction(rootfsPath, resultPath, imageName string, runner Runner)
 // E.g.
 // CGO_ENABLED=0 go build -ldflags '-extldflags "-static"' -o build/enki && docker run -it -e PATH=/kaniko -v /tmp -v /home/dimitris/workspace/kairos/osbuilder/tmp/rootfs/:/context -v "$PWD/build/enki":/enki -v $PWD:/build --rm --entrypoint "/enki" gcr.io/kaniko-project/executor:latest convert /context
 func (ca *ConverterAction) Run() (err error) {
-	dockerfile, err := ca.createDockerfile()
+	da := NewDockerfileAction(ca.rootFSPath, "")
+	dockerfile, err := da.Run()
 	if err != nil {
-		return
+		return err
 	}
 	defer os.Remove(dockerfile)
 
@@ -75,40 +76,6 @@ func (ca *ConverterAction) Run() (err error) {
 	return
 }
 
-func (ca *ConverterAction) createDockerfile() (string, error) {
-	f, err := os.CreateTemp("", "")
-	if err != nil {
-		return "", err
-	}
-	defer f.Close()
-
-	// write data to the temporary file
-	data := []byte(`
-FROM busybox as builder
-RUN mkdir /rootfs
-COPY . /rootfs/.
-
-RUN echo "nameserver 8.8.8.8" > /rootfs/etc/resolv.conf
-RUN cat /rootfs/etc/resolv.conf
-
-FROM scratch as rootfs
-
-COPY --from=builder /rootfs/ .
-
-FROM rootfs
-
-# TODO: Do more clever things
-RUN apt-get update && apt-get install -y curl
-`)
-
-	if _, err := f.Write(data); err != nil {
-		os.Remove(f.Name())
-		return "", err
-	}
-
-	return f.Name(), nil
-}
-
 // https://github.com/GoogleContainerTools/kaniko/issues/1007
 // Create a .dockerignore in the rootfs directory to skip these:
 // https://github.com/GoogleContainerTools/kaniko/pull/1724/files#diff-1e90758e2fb0f26bdbfe7a40aafc4b4796cbf808842703e52e16c1f36b8da7dcR89

pkg/action/dockerfile.go

@@ -1,6 +1,9 @@
 package action
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 // ConverterAction is the action that converts a non-kairos image to a Kairos one.
 // The conversion happens in a best-effort manner. It's not guaranteed that
@@ -21,9 +24,72 @@ func NewDockerfileAction(rootfsPath, baseImageURI string) *DockerfileAction {
 }
 
 func (a *DockerfileAction) Run() (dockerfile string, err error) {
-	if a.rootFSPath != "" && a.baseImageURI != "" {
-		return "", errors.New("only one of 'rootfs-dir' and 'base-image-uri' should be defined")
+	if err := a.Validate(); err != nil {
+		return "", err
 	}
 
-	return "", nil
+	dockerfile = ""
+	dockerfile += a.baseImageSection()
+	dockerfile += a.dnsSection()
+	dockerfile += a.footerSection()
+	dockerfile += a.osSpecificSection()
+
+	return dockerfile, nil
+}
+
+func (a *DockerfileAction) baseImageSection() string {
+	result := ""
+	if a.baseImageURI != "" {
+		return fmt.Sprintf(`
+FROM %s as base
+FROM busybox as builder
+
+COPY --from=base . /rootfs
+
+FROM rootfs
+# Additional os specific things
+`, a.baseImageURI)
+	}
+
+	result = fmt.Sprintf(`
+FROM busybox as builder
+RUN mkdir /rootfs
+COPY %s /rootfs/.
+
+FROM rootfs
+# Additional os specific things
+`, a.rootFSPath)
+
+	return result
+}
+
+func (a *DockerfileAction) dnsSection() string {
+	return `
+RUN echo "nameserver 8.8.8.8" > /rootfs/etc/resolv.conf
+RUN cat /rootfs/etc/resolv.conf
+`
+}
+
+func (a *DockerfileAction) footerSection() string {
+	return `
+FROM scratch as rootfs
+
+COPY --from=builder /rootfs/ .
+`
+}
+
+func (a *DockerfileAction) osSpecificSection() string {
+	return `
+FROM rootfs
+# Additional os specific things
+`
+}
+
+func (a *DockerfileAction) Validate() error {
+	if a.rootFSPath != "" && a.baseImageURI != "" ||
+		a.rootFSPath == "" && a.baseImageURI == "" {
+		return errors.New("exactly one of 'rootfs-dir' and 'base-image-uri' should be defined")
+	}
+
+	return nil
 }