Makefile: use official alpine images for build

This commit modifies the build tooling so that we use the official
alipne build images rather than the images from the multiarch org. This
requires new logic to parse docker manifests but results in a cleaner
solution with fewer architecture definitions.

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

.travis.yml

@@ -13,6 +13,9 @@ go:
 env:
   - GO111MODULE=on DOCKER_CLI_EXPERIMENTAL=enabled
 
+before_install:
+  - sudo apt-get update && sudo apt-get -y install jq
+
 install: true
 
 script:

Makefile

@@ -3,8 +3,7 @@ export GO111MODULE=on
 
 ARCH ?= amd64
 ALL_ARCH := amd64 arm arm64
-DOCKER_ARCH := "" "arm v7" "arm64 v8"
-IMAGE_ARCH := amd64 armhf arm64
+DOCKER_ARCH := "amd64" "arm v7" "arm64 v8"
 BINS := $(addprefix bin/$(ARCH)/,kg kgctl)
 PROJECT := kilo
 PKG := github.com/squat/$(PROJECT)
@@ -34,6 +33,7 @@ OPENAPI_GEN_BINARY := bin/openapi-gen
 GOLINT_BINARY := bin/golint
 
 BUILD_IMAGE ?= golang:1.13.4-alpine
+BASE_IMAGE ?= alpine:3.11
 
 build: $(BINS)
 
@@ -203,9 +203,12 @@ header: .header
 container: .container-$(ARCH)-$(VERSION) container-name
 .container-$(ARCH)-$(VERSION): $(BINS) Dockerfile
 	@i=0; for a in $(ALL_ARCH); do [ "$$a" = $(ARCH) ] && break; i=$$((i+1)); done; \
-	ia=""; \
-	j=0; for a in $(IMAGE_ARCH); do [ "$$i" -eq "$$j" ] && ia="$$a" && break; j=$$((j+1)); done; \
-	docker build -t $(IMAGE):$(ARCH)-$(VERSION) --build-arg FROM=multiarch/alpine:$$ia-v3.11 --build-arg GOARCH=$(ARCH) .
+	ia=""; iv=""; \
+	j=0; for a in $(DOCKER_ARCH); do \
+	    [ "$$i" -eq "$$j" ] && ia=$$(echo "$$a" | awk '{print $$1}') && iv=$$(echo "$$a" | awk '{print $$2}') && break; j=$$((j+1)); \
+	done; \
+	SHA=$$(docker manifest inspect $(BASE_IMAGE) | jq '.manifests[] | select(.platform.architecture == "'$$ia'") | if .platform | has("variant") then select(.platform.variant == "'$$iv'") else . end | .digest' -r); \
+	docker build -t $(IMAGE):$(ARCH)-$(VERSION) --build-arg FROM=$(BASE_IMAGE)@$$SHA --build-arg GOARCH=$(ARCH) .
 	@docker images -q $(IMAGE):$(ARCH)-$(VERSION) > $@
 
 container-latest: .container-$(ARCH)-$(VERSION)