use dep to resolve dependencies and cache the vendor libs

.dockerignore

@@ -0,0 +1 @@
+vendor

Dockerfile

@@ -1,13 +1,19 @@
 # build stage
 FROM ataraev/golang-alpine-git AS build-env
-ADD . /go/app
-WORKDIR /go/app
 ENV GOBIN /go/bin
-RUN go get -d -v ./
+RUN apk add --update openssl && \ 
+    wget -O /go/bin/dep http://github.com/golang/dep/releases/download/v0.3.2/dep-linux-amd64 && \
+    chmod +x /go/bin/dep
+
+COPY ./Gopkg.* /go/src/github.com/lawrencegripper/traefik-appinsights-watchdog/
+WORKDIR /go/src/github.com/lawrencegripper/traefik-appinsights-watchdog
+RUN dep ensure --vendor-only -v
+
+COPY . /go/src/github.com/lawrencegripper/traefik-appinsights-watchdog/
 RUN go build -o traefik-appinsights-watchdog -v
 
 # final stage
 FROM golang:alpine
 WORKDIR /app
-COPY --from=build-env /go/app/traefik-appinsights-watchdog .
+COPY --from=build-env /go/src/github.com/lawrencegripper/traefik-appinsights-watchdog/traefik-appinsights-watchdog .
 ENTRYPOINT ["./traefik-appinsights-watchdog"]