chore(docker): properly handle arm(32) and arm64 (grafana#441)

* chore(docker): install Helm from binary

Reverts the previous commits attempt to fix Helm on arm32 by using the
Alpine package, because as it turns out, there is no alpine package for
armhf.

Instead, we now use the offical Helm binaries, and `go env GOOS` and `go
env GOARCH` to pick the correct one.

This should work consistently across all platforms.

* fix(docker): use golang:alpine

Uses the alpine version of golang consistently across the whole
Dockerfile, so no longer need to pull both, the ubuntu and the alpine
variant: use golang:alpine

Uses the alpine version of golang consistently across the whole
Dockerfile, so no longer need to pull both, the ubuntu and the alpine variant

* chore(docker): kubectl on arm

Dockerfile

@@ -1,27 +1,36 @@
 # download kubectl
-FROM alpine as kubectl
+FROM golang:alpine as kubectl
 RUN apk add --no-cache curl
 RUN export VERSION=$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt) &&\
-    curl -o /usr/local/bin/kubectl -L https://storage.googleapis.com/kubernetes-release/release/${VERSION}/bin/linux/amd64/kubectl &&\
+    export OS=$(go env GOOS) && \
+    export ARCH=$(go env GOARCH) &&\
+    curl -o /usr/local/bin/kubectl -L https://storage.googleapis.com/kubernetes-release/release/${VERSION}/bin/${OS}/${ARCH}/kubectl &&\
     chmod +x /usr/local/bin/kubectl
 
 # build jsonnet-bundler
-FROM golang as jb
+FROM golang:alpine as jb
 WORKDIR /tmp
-RUN git clone https://github.com/jsonnet-bundler/jsonnet-bundler &&\
+RUN apk add --no-cache git make bash &&\
+    git clone https://github.com/jsonnet-bundler/jsonnet-bundler &&\
     cd jsonnet-bundler &&\
     make static &&\
     mv _output/jb /usr/local/bin/jb
 
-FROM alpine as helm
-RUN apk add --no-cache -X http://dl-cdn.alpinelinux.org/alpine/edge/testing helm
+FROM golang:alpine as helm
+WORKDIR /tmp/helm
+RUN apk add --no-cache jq curl
+RUN export TAG=$(curl --silent "https://api.github.com/repos/helm/helm/releases/latest" | jq -r .tag_name) &&\
+    export OS=$(go env GOOS) &&\
+    export ARCH=$(go env GOARCH) &&\
+    curl -SL "https://get.helm.sh/helm-${TAG}-${OS}-${ARCH}.tar.gz" > helm.tgz && \
+    tar -xvf helm.tgz --strip-components=1
 
 # assemble final container
 FROM alpine
 RUN apk add --no-cache coreutils diffutils less git openssh-client
 COPY tk /usr/local/bin/tk
 COPY --from=kubectl /usr/local/bin/kubectl /usr/local/bin/kubectl
 COPY --from=jb /usr/local/bin/jb /usr/local/bin/jb
-COPY --from=helm /usr/bin/helm /usr/local/bin/helm
+COPY --from=helm /tmp/helm/helm /usr/local/bin/helm
 WORKDIR /app
 ENTRYPOINT ["/usr/local/bin/tk"]