osbuilder: Revert to using apk.static for Alpine

#2399 partially reverted #418, missing on returning to bootstrapping a
rootfs with `apk.static` instead of copying the entire root, which can
result in drastically larger (more than 10x) images. Revert this as well
(requires some updates to URL building).

Fixes: #3216
Signed-off-by: Jakob Naucke <jakob.naucke@ibm.com>

tools/osbuilder/rootfs-builder/alpine/config.sh

@@ -11,7 +11,7 @@ BASE_PACKAGES="alpine-base"
 
 # Alpine mirror to use
 # See a list of mirrors at http://nl.alpinelinux.org/alpine/MIRRORS.txt
-MIRROR=http://dl-5.alpinelinux.org/alpine
+MIRROR=https://dl-5.alpinelinux.org/alpine
 
 PACKAGES=""
 

tools/osbuilder/rootfs-builder/alpine/rootfs_lib.sh

@@ -9,6 +9,8 @@
 #
 # - Optional environment variables
 #
+# EXTRA_PKGS: Variable to add extra PKGS provided by the user
+#
 # BIN_AGENT: Name of the Kata-Agent binary
 #
 # Any other configuration variable for a specific distro must be added
@@ -22,13 +24,20 @@ build_rootfs() {
 	# Mandatory
 	local ROOTFS_DIR=$1
 
+	# Add extra packages to the rootfs when specified
+	local EXTRA_PKGS=${EXTRA_PKGS:-}
+
 	# Populate ROOTFS_DIR
 	check_root
 	mkdir -p "${ROOTFS_DIR}"
 
-	rm -rf ${ROOTFS_DIR}/var/tmp
-	cp -a -r -f /bin /etc /lib /sbin /usr /var ${ROOTFS_DIR}
-	mkdir -p ${ROOTFS_DIR}{/root,/proc,/dev,/home,/media,/mnt,/opt,/run,/srv,/sys,/tmp}
+	/sbin/apk.static \
+	    -X ${MIRROR}/v${OS_VERSION}/main \
+	    -U \
+	    --allow-untrusted \
+	    --root ${ROOTFS_DIR} \
+	    --initdb add ${BASE_PACKAGES} ${EXTRA_PKGS} ${PACKAGES}
 
-	echo "${MIRROR}/${OS_VERSION}/main" >  ${ROOTFS_DIR}/etc/apk/repositories
+	mkdir -p ${ROOTFS_DIR}{/root,/etc/apk,/proc}
+	echo "${MIRROR}/v${OS_VERSION}/main" >  ${ROOTFS_DIR}/etc/apk/repositories
 }