Add multi-arch build script

.dockerignore

@@ -6,3 +6,4 @@ dumpcerts.sh
 acme.json
 acme-backup.json
 traefik-certs-dumper
+build-docker.sh

Dockerfile

@@ -1,5 +1,10 @@
 FROM golang:1-alpine as builder
 
+ARG RUNTIME_HASH
+ARG GOARCH
+ARG GOARM
+ARG GOOS
+
 RUN apk --update upgrade \
     && apk --no-cache --no-progress add git make gcc musl-dev
 
@@ -10,9 +15,9 @@ COPY go.mod go.sum ./
 RUN go mod download
 
 COPY . .
-RUN make build
+RUN GOARCH=${GOARCH} GOARM=${GOARM} GOOS=${GOOS} make build
 
-FROM alpine:3.9
+FROM alpine:3.9${RUNTIME_HASH}
 RUN apk --update upgrade \
     && apk --no-cache --no-progress add ca-certificates
 

build-docker.sh

@@ -0,0 +1,76 @@
+#!/bin/bash
+set -ex
+
+# base docker image tag
+TAG="andig/traefik-certs-dumper"
+
+# only linux for now
+OS=linux
+
+# target platforms in docker manifest notation
+declare -a PLATFORMS=( "amd64" "arm.v6" )
+
+# images from Dockerfile
+IMAGE=$(grep "FROM alpine" < Dockerfile | sed "s/FROM //" | sed 's/\$.*//')
+
+# manifest cache file
+MANIFEST_FILE=/tmp/manifest.$IMAGE.json
+
+# get platform image hash from docker manifest
+function hash () {
+    local ARCHITECTURE VARIANT HASH
+    read -r ARCHITECTURE VARIANT <<< "$@"
+
+    if [ -z "$VARIANT" ]; then
+        HASH=$(jq -r ".manifests[] | select(.platform.architecture == \"$ARCHITECTURE\") | .digest" < "$MANIFEST_FILE")
+    else
+        HASH=$(jq -r ".manifests[] | select(.platform.architecture == \"$ARCHITECTURE\" and .platform.variant == \"$VARIANT\") | .digest" < "$MANIFEST_FILE")
+    fi
+
+    echo "$HASH"
+}
+
+# get manifest
+if [ ! -f "$MANIFEST_FILE" ]; then
+    docker pull "$IMAGE"
+    docker manifest inspect "$IMAGE" > "$MANIFEST_FILE"
+fi
+
+# main
+for platform in "${PLATFORMS[@]}"; do 
+    # split architecture.version
+    IFS='.' read -r ARCHITECTURE VARIANT <<< "$platform"
+
+    # add xargs to trim whitespace
+    RUNTIME_HASH=$(hash "$ARCHITECTURE" "$VARIANT")
+
+    # arm architectures flavors, strip "v" prefix
+    GOARM=${VARIANT:1}
+
+    # build for target runtime image and architecture
+    docker build --build-arg RUNTIME_HASH=@${RUNTIME_HASH} --build-arg GOARCH=${ARCHITECTURE} --build-arg GOARM=${GOARM} -t "$TAG:latest-$platform" .
+done
+
+# push images
+for platform in "${PLATFORMS[@]}"; do 
+    docker push "$TAG:latest-$platform"
+done
+
+# create manifest
+TAG_LIST=$(printf "$TAG:latest-%s " "${PLATFORMS[@]}")
+# shellcheck disable=SC2086
+docker manifest create --amend "$TAG:latest" $TAG_LIST
+
+for platform in "${PLATFORMS[@]}"; do 
+    # split architecture.version
+    IFS='.' read -r ARCHITECTURE VARIANT <<< "$platform"
+    
+    # docker and go architectures don't match
+    if [ "arm" == "$ARCHITECTURE" ] && [ -n "$VARIANT" ]; then
+        VARIANT="$ARCHITECTURE$VARIANT"
+    fi
+
+    docker manifest annotate "$TAG:latest" "$TAG:latest-$platform" --os "$OS" --arch "$ARCHITECTURE" --variant "$VARIANT"
+done
+
+docker manifest push "$TAG:latest"