fix: squash image layers during build

close #75

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

Author: Adphi

templates/alpine.Dockerfile

@@ -1,4 +1,4 @@
-FROM {{ .Image }}
+FROM {{ .Image }} AS rootfs
 
 USER root
 
@@ -48,3 +48,7 @@ RUN apk add --no-cache  \
 {{- end }}
     grub
 {{- end }}
+
+FROM scratch
+
+COPY --from=rootfs / /

templates/centos.Dockerfile

@@ -1,4 +1,4 @@
-FROM {{ .Image }}
+FROM {{ .Image }} AS rootfs
 
 USER root
 
@@ -46,3 +46,7 @@ RUN cd /boot && \
 
 RUN yum clean all && \
     rm -rf /var/cache/yum
+
+FROM scratch
+
+COPY --from=rootfs / /

templates/debian.Dockerfile

@@ -1,4 +1,4 @@
-FROM {{ .Image }}
+FROM {{ .Image }} AS rootfs
 
 USER root
 
@@ -77,3 +77,7 @@ RUN mv $(ls -t /boot/vmlinuz-* | head -n 1) /boot/vmlinuz && \
 
 RUN apt-get clean && \
     rm -rf /var/lib/apt/lists/*
+
+FROM scratch
+
+COPY --from=rootfs / /

templates/ubuntu.Dockerfile

@@ -1,4 +1,4 @@
-FROM {{ .Image }}
+FROM {{ .Image }} as rootfs
 
 USER root
 
@@ -68,3 +68,7 @@ RUN mv $(ls -t /boot/vmlinuz-* | head -n 1) /boot/vmlinuz && \
 
 RUN apt-get clean && \
     rm -rf /var/lib/apt/lists/*
+
+FROM scratch
+
+COPY --from=rootfs / /