.travis.yml: create multi arch image and docker manifest

Now you can just pull the image from an arm64 (armV8), arm(armV7) or amd64 architecture without specifying any tag.

.travis.yml

@@ -7,6 +7,16 @@ services:
 
 script:
   - docker login -u="$DOCKER_USER" -p="$DOCKER_PW" https://flotte-docker-registry.spdns.org/
-  - docker build -t frontend-server .
+  - docker build -t frontend-server:amd64 . --build-arg ARCH=amd64
-  - docker tag frontend-server flotte-docker-registry.spdns.org/frontend-server
+  - docker build -t frontend-server:arm . --build-arg ARCH=arm
-  - docker push flotte-docker-registry.spdns.org/frontend-server:latest
+  - docker build -t frontend-server:arm64 . --build-arg ARCH=arm64
+  - docker tag frontend-server:amd64 flotte-docker-registry.spdns.org/frontend-server:amd64
+  - docker push flotte-docker-registry.spdns.org/frontend-server:amd64
+  - docker tag frontend-server flotte-docker-registry.spdns.org/frontend-server:arm64
+  - docker push flotte-docker-registry.spdns.org/frontend-server:arm64
+  - docker tag frontend-server flotte-docker-registry.spdns.org/frontend-server:arm
+  - docker push flotte-docker-registry.spdns.org/frontend-server:arm
+  - docker manifest create --amend flotte-docker-registry.spdns.org/frontend-server:latest flotte-docker-registry.spdns.org/frontend-server:arm flotte-docker-registry.spdns.org/frontend-server:arm64 flotte-docker-registry.spdns.org/frontend-server:amd64
+  - docker manifest annotate flotte-docker-registry.spdns.org/frontend-server:latest flotte-docker-registry.spdns.org/frontend-server:arm --os linux --arch arm --variant v7 
+  - docker manifest annotate flotte-docker-registry.spdns.org/frontend-server:latest flotte-docker-registry.spdns.org/frontend-server:arm64 --os linux --arch arm64 --variant v8 
+  - docker manifest push flotte-docker-registry.spdns.org/frontend-server:latest

Dockerfile

@@ -9,6 +9,7 @@ COPY . .
 RUN ng build --prod --crossOrigin=anonymous
 
 FROM golang:1.13.4-alpine as builder2
+ENV ARCH=amd64
 RUN apk add git
 WORKDIR /
 COPY --from=builder /frontend/dist /dist 
@@ -16,7 +17,7 @@ RUN go get github.com/rakyll/statik
 RUN statik --src=/dist/flotte-frontend
 COPY *.go *.sum *.mod /
 COPY vendor /vendor
-RUN CGO_ENABLED=0 GOOS=linux go build --mod=vendor -o frontend_server
+RUN CGO_ENABLED=0 GOARCH=$ARCH GOOS=linux go build --mod=vendor -o frontend_server
 
 FROM scratch
 WORKDIR /