Rewrite dockerfile to use alpine (#8)

* Rewrite dockerfile to use alpine

* use nproc instead of hardcoded 8

* remove redundant chown

Dockerfile

@@ -1,12 +1,19 @@
-FROM golang AS build
+FROM golang:alpine AS build
 
 WORKDIR /usr/gateway
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
-RUN go build -o build/gateway
+# https://github.com/valyala/gozstd/issues/20
+RUN apk add gcc musl-dev libc-dev make && \
+    GOZSTD_VER=$(cat go.mod | fgrep github.com/valyala/gozstd | awk '{print $NF}') && \
+    go get -d github.com/valyala/gozstd@${GOZSTD_VER} && \
+    cd ${GOPATH}/pkg/mod/github.com/valyala/gozstd@${GOZSTD_VER} && \
+    make clean && \
+    make -j $(nproc) libzstd.a && \
+    cd /usr/gateway && \
+    go build -o build/gateway
 
-FROM debian:buster-slim AS runtime
-RUN apt-get update -y && apt-get install -y ca-certificates
+FROM alpine:latest
 COPY --from=build /usr/gateway/build/gateway /gateway
 ENTRYPOINT ["/gateway"]