Add support for ARM64

Dockerfile

@@ -1,7 +1,9 @@
 # SPDX-FileCopyrightText: 2020 SAP SE or an SAP affiliate company and Gardener contributors
 # SPDX-License-Identifier: Apache-2.0
 
-FROM gcr.io/etcd-development/etcd:v3.4.18
+FROM gcr.io/etcd-development/etcd:v3.4.18 as source-amd64
+FROM gcr.io/etcd-development/etcd:v3.4.18-arm64 as source-arm64
+FROM source-$TARGETARCH as source
 
 RUN apt update
 RUN apt install -y bash curl wget

Dockerfile.template

@@ -1,7 +1,10 @@
 # SPDX-FileCopyrightText: 2020 SAP SE or an SAP affiliate company and Gardener contributors
 # SPDX-License-Identifier: Apache-2.0
 
-FROM gcr.io/etcd-development/etcd:ETCD_VERSION
+FROM gcr.io/etcd-development/etcd:ETCD_VERSION as source-amd64
+FROM gcr.io/etcd-development/etcd:ETCD_VERSION as source-arm64
+
+FROM source-$TARGETARCH
 
 RUN apt update
 RUN apt install -y bash curl wget

etcd_bootstrap_script.sh

@@ -22,6 +22,12 @@ trap_and_propagate() {
 }
 
 start_managed_etcd(){
+      arch=$(uname -m)
+      if [ $arch = "aarch64" ] || [ $arch = "arm64" ]; then
+          # Running etcd on ARM has experimental support for version 3.4.x
+          # https://etcd.io/docs/v3.4/op-guide/supported-platform/
+          export ETCD_UNSUPPORTED_ARCH=arm64
+      fi
       rm -rf $VALIDATION_MARKER
       CONFIG_FILE=/etc/etcd.conf.yaml
       curl "$BACKUP_ENDPOINT/config" -o $CONFIG_FILE