Makefile,build_docker.sh: allow to configure target platform. (#10806)

Build dev tailscale and k8s-operator images for linux/amd64 only by default,
make it possible to configure target build platform via PLATFORM var.

Updates#cleanup

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

Makefile

@@ -3,6 +3,8 @@ SYNO_ARCH ?= "amd64"
 SYNO_DSM ?= "7"
 TAGS ?= "latest"
 
+PLATFORM ?= "flyio" ## flyio==linux/amd64. Set to "" to build all platforms.
+
 vet: ## Run go vet
 	./tool/go vet ./...
 
@@ -88,7 +90,7 @@ publishdevimage: ## Build and publish tailscale image to location specified by $
 	@test "${REPO}" != "ghcr.io/tailscale/tailscale" || (echo "REPO=... must not be ghcr.io/tailscale/tailscale" && exit 1)
 	@test "${REPO}" != "tailscale/k8s-operator" || (echo "REPO=... must not be tailscale/k8s-operator" && exit 1)
 	@test "${REPO}" != "ghcr.io/tailscale/k8s-operator" || (echo "REPO=... must not be ghcr.io/tailscale/k8s-operator" && exit 1)
-	TAGS="${TAGS}" REPOS=${REPO} PUSH=true TARGET=client ./build_docker.sh
+	TAGS="${TAGS}" REPOS=${REPO} PLATFORM=${PLATFORM} PUSH=true TARGET=client ./build_docker.sh
 
 publishdevoperator: ## Build and publish k8s-operator image to location specified by ${REPO}
 	@test -n "${REPO}" || (echo "REPO=... required; e.g. REPO=ghcr.io/${USER}/tailscale" && exit 1)
@@ -96,7 +98,7 @@ publishdevoperator: ## Build and publish k8s-operator image to location specifie
 	@test "${REPO}" != "ghcr.io/tailscale/tailscale" || (echo "REPO=... must not be ghcr.io/tailscale/tailscale" && exit 1)
 	@test "${REPO}" != "tailscale/k8s-operator" || (echo "REPO=... must not be tailscale/k8s-operator" && exit 1)
 	@test "${REPO}" != "ghcr.io/tailscale/k8s-operator" || (echo "REPO=... must not be ghcr.io/tailscale/k8s-operator" && exit 1)
-	TAGS="${TAGS}" REPOS=${REPO} PUSH=true TARGET=operator ./build_docker.sh
+	TAGS="${TAGS}" REPOS=${REPO} PLATFORM=${PLATFORM} PUSH=true TARGET=operator ./build_docker.sh
 
 help: ## Show this help
 	@echo "\nSpecify a command. The choices are:\n"

build_docker.sh

@@ -32,6 +32,7 @@ PUSH="${PUSH:-false}"
 TARGET="${TARGET:-${DEFAULT_TARGET}}"
 TAGS="${TAGS:-${DEFAULT_TAGS}}"
 BASE="${BASE:-${DEFAULT_BASE}}"
+PLATFORM="${PLATFORM:-}" # default to all platforms
 
 case "$TARGET" in
   client)
@@ -50,6 +51,7 @@ case "$TARGET" in
       --tags="${TAGS}" \
       --repos="${REPOS}" \
       --push="${PUSH}" \
+      --target="${PLATFORM}" \
       /usr/local/bin/containerboot
     ;;
   operator)
@@ -65,6 +67,7 @@ case "$TARGET" in
       --tags="${TAGS}" \
       --repos="${REPOS}" \
       --push="${PUSH}" \
+      --target="${PLATFORM}" \
       /usr/local/bin/operator
     ;;
   *)