Dockerfile: change Alpine pkg CDN

The current Alpine package CDN is timing out for aarch64. This commit
updates it to another mirror. This commit also changes the channel
Alpine channel from edge to v3.12. Note: the Dockerfile overrides the
Alpine CDN settings to ensure that a mirror with support for TLS is
used.

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

Dockerfile

@@ -8,7 +8,7 @@ RUN apk add --no-cache curl && \
 FROM $FROM
 ARG GOARCH
 LABEL maintainer="squat <lserven@gmail.com>"
-RUN echo -e "https://dl-3.alpinelinux.org/alpine/edge/main\nhttps://dl-3.alpinelinux.org/alpine/edge/community" > /etc/apk/repositories && \
+RUN echo -e "https://alpine.global.ssl.fastly.net/alpine/v3.12/main\nhttps://alpine.global.ssl.fastly.net/alpine/v3.12/community" > /etc/apk/repositories && \
     apk add --no-cache ipset iptables ip6tables wireguard-tools
 COPY --from=cni bridge host-local loopback portmap /opt/cni/bin/
 COPY bin/$GOARCH/kg /opt/bin/

Makefile

@@ -33,7 +33,7 @@ OPENAPI_GEN_BINARY := bin/openapi-gen
 GOLINT_BINARY := bin/golint
 
 BUILD_IMAGE ?= golang:1.14.2-alpine
-BASE_IMAGE ?= alpine:3.11
+BASE_IMAGE ?= alpine:3.12
 
 build: $(BINS)