capi/Makefile: support all Flatcar Container Linux channels

This change adds support for building all channels of Flatcar
Container Linux. It also fixes an issue that made the build fail
when make was called directly instead of using the wrapper script
hack/image-build-flatcar.sh.

images/capi/Makefile

@@ -122,10 +122,17 @@ PACKER_VAR_FILES := $(foreach f,$(abspath $(PACKER_VAR_FILES)),-var-file="$(f)"
 ## Platform and version combinations
 ## --------------------------------------
 CENTOS_VERSIONS			:=	centos-7
-FLATCAR_VERSIONS			:=	flatcar-stable
+FLATCAR_VERSIONS			:=	flatcar
 PHOTON_VERSIONS			:=	photon-3
 UBUNTU_VERSIONS			:=	ubuntu-1804 ubuntu-2004
 
+# Set Flatcar Container Linux channel and version if not supplied
+FLATCAR_CHANNEL ?= stable
+FLATCAR_VERSION ?= $(shell hack/image-grok-latest-flatcar-version.sh $(FLATCAR_CHANNEL))
+
+export FLATCAR_CHANNEL FLATCAR_VERSION
+
+
 PLATFORMS_AND_VERSIONS	:=	$(CENTOS_VERSIONS) \
 							$(FLATCAR_VERSIONS) \
 							$(PHOTON_VERSIONS) \
@@ -144,7 +151,7 @@ AZURE_BUILD_NAMES		?=	azure-sig-ubuntu-1804 azure-vhd-ubuntu-1804
 
 DO_BUILD_NAMES 			?=	do-default
 
-QEMU_BUILD_NAMES			?=	qemu-flatcar-stable qemu-ubuntu-1804
+QEMU_BUILD_NAMES			?=	qemu-flatcar qemu-ubuntu-1804
 
 ## --------------------------------------
 ## Dynamic build targets

images/capi/README-flatcar.md

@@ -31,11 +31,24 @@ Before running `packer build` command, please make sure the following:
 
 ## Usage
 
-Provisioning and `kubeadm` initialisation is automated; start a new build with
+Flatcar qemu images can be built using the Makefile; a convenience wrapper
+script is provided to import the VM into vagrant and to initialise `kubeadm`.
+
+### Convenience wrapper script
+
+The wrapper script will call `make` (see below) to build an image,
+import the image to vagrant, start a VM, and initialise `kubeadm`. After the
+script concluded, users are all set up and can start interacting with kubernetes.
+
+Start a new build with
 ```shell
 ./hack/image-build-flatcar.sh [<channel>] [<release-version>]
 ```
 
+Flatcar Container Linux maintains four distinct
+channels: `alpha`, `beta`, `stable`, and `edge`. For details please refer to
+the [releases page](https://www.flatcar-linux.org/releases/).
+
 The build script will default to the latest release of the `stable` channel.
 
 After provisioning concluded the script will ask you to export flatcar channel
@@ -54,6 +67,25 @@ Kubernetes master is running at https://10.0.2.15:6443
 KubeDNS is running at https://10.0.2.15:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
 ```
 
+Get an overview of all images built by using `hack/boxes-flatcar.sh`. The
+helper script will list all available images / VMs and will output environment
+variables for convenient copy/paste.
+
+### Makefile build
+
+Make target `build-qemu-flatcar` will build a Flatcar Container Linux qemu
+image. The make variables `FLATCAR_CHANNEL` and `FLATCAR_VERSION` can be set to
+build specific releases. THe build will default to the current stable release.
+
+Example usage:
+```shell
+$ make build-qemu-flatcar
+or
+$ make FLATCAR_CHANNEL=beta build-qemu-flatcar
+or
+$ make FLATCAR_CHANNEL=stable FLATCAR_VERSION=2512.2.0 build-qemu-flatcar
+```
+
 ## Notes
 
 * It needs to disable `gather_facts` in `images/capi/ansible/node.yml`, because it is not possible to run python before running setup tasks. Note that python is not installed by default in Flatcar.

images/capi/hack/image-build-flatcar.sh

@@ -1,8 +1,5 @@
 #!/bin/sh -e
 
-set -e
-#set -u
-
 usage() {
     echo "Usage: $0 [<channel>] [<version>]"
     echo "          <channel> is one of: edge alpha beta stable (defaults to"
@@ -12,12 +9,13 @@ usage() {
 }
 # --
 
-list_releases() {
+check_for_release() {
+    channel="$1"
+    release="$2"
     curl -s \
-         "https://www.flatcar-linux.org/releases-json/releases-$1.json" \
+         "https://www.flatcar-linux.org/releases-json/releases-$channel.json" \
         | jq -r 'to_entries[] | "\(.key)"' \
-        | grep -v "current" \
-        | sort 
+        | grep -q "$release"
 }
 # --
 
@@ -34,13 +32,14 @@ case $channel in
 esac
 
 release="$2"
-if [ -z "$release" ] ; then
-    release=$(list_releases "$channel" | tail -n1)
-else
-    list_releases "$channel" | grep -q "$release" || {
+if [ -n "$release" ] ; then
+    check_for_release "$channel" "$release" || {
         echo "Unknown release '$release' for channel '$channel'."
         usage
         exit 1; }
+else
+    release="$(\
+       "$(dirname "$0")"/image-grok-latest-flatcar-version.sh "$channel")"
 fi
 
 
@@ -53,9 +52,8 @@ export FLATCAR_CHANNEL FLATCAR_VERSION
 
 rm -rf ./output/flatcar-"${channel}-${release}"-kube-*
 
-# for now the Makefile only supports flatcar-stable.
-# TODO: make it support multiple channels and versions
-make build-qemu-flatcar-stable
+make FLATCAR_CHANNEL="$channel" FLATCAR_VERSION="$release" \
+                                                    build-qemu-flatcar
 
 echo "#### Importing $channel-$release box to vagrant and setting up kubeadm."
 

images/capi/hack/image-grok-latest-flatcar-version.sh

@@ -0,0 +1,10 @@
+#!/bin/sh -ue
+
+channel="$1"
+
+curl -s \
+     "https://www.flatcar-linux.org/releases-json/releases-$channel.json" \
+    | jq -r 'to_entries[] | "\(.key)"' \
+    | grep -v "current" \
+    | sort \
+    | tail -n1