fix: don't hardcode docker-gen tag in dockerfile

The Dockerfile now builds from the actual surrounding sources

Author: buchdag

Dockerfile

@@ -1,28 +1,27 @@
 # Build docker-gen from scratch
-FROM golang:1.14-alpine as dockergen
-RUN apk add --no-cache git
+FROM golang:1.16-alpine as go-builder
 
-# Download the sources for the given version
-ENV VERSION 0.7.5
-ADD https://github.com/jwilder/docker-gen/archive/${VERSION}.tar.gz sources.tar.gz
+ARG VERSION=master
 
-# Move the sources into the right directory
-RUN tar -xzf sources.tar.gz && \
-   mkdir -p /go/src/github.com/jwilder/ && \
-   mv docker-gen-* /go/src/github.com/jwilder/docker-gen
+WORKDIR /build
 
-# Install the dependencies and make the docker-gen executable
-WORKDIR /go/src/github.com/jwilder/docker-gen
-RUN CGO_ENABLED=0 go build -ldflags "-X main.buildVersion=${VERSION}" ./cmd/docker-gen
+# Install the dependencies
+COPY . .
+RUN go mod download -json
 
-FROM alpine:latest
-LABEL maintainer="Jason Wilder <[email protected]>"
+# Build the docker-gen executable
+RUN CGO_ENABLED=0 go build -ldflags "-X main.buildVersion=${VERSION}" -o docker-gen ./cmd/docker-gen
+
+FROM alpine:3.13
 
-RUN apk -U add openssl
+LABEL maintainer="Jason Wilder <[email protected]>"
 
-ENV VERSION 0.7.5
-COPY --from=dockergen /go/src/github.com/jwilder/docker-gen/docker-gen /usr/local/bin/docker-gen
 ENV DOCKER_HOST unix:///tmp/docker.sock
 
+# Install packages required by the image
+RUN apk add --no-cache --virtual .bin-deps openssl
+
+# Install docker-gen from build stage
+COPY --from=go-builder /build/docker-gen /usr/local/bin/docker-gen
 
-ENTRYPOINT ["/usr/local/bin/docker-gen"]
+ENTRYPOINT ["/usr/local/bin/docker-gen"]