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optimize docker image size #76

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Mar 13, 2016
Merged

optimize docker image size #76

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14 changes: 14 additions & 0 deletions Rockerfile
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# build image
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the magic of Rocker is we can separate the build and runtime image.
the build image container all resource or dependencies required at build time.
once the build success, copy it to the runtime image which based on alpine.
so the final image is alpine + MailHog executable binary.

FROM golang:latest
RUN go get -v github.com/mailhog/MailHog && \
cd /go/src && \
CGO_ENABLED=0 go build -a -installsuffix cgo -v -o /go/bin/MailHog.o github.com/mailhog/MailHog/main.go
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use go get to download the main.go and all dependencies first.
then build the binary.

Since alpine linux and therefor gliderlabs/alpine docker containers use musl instead of gnu libc your golang binaries will not work inside alpine. so we need build with static linking enabled.
see also: http://www.blang.io/posts/2015-04_golang-alpine-build-golang-binaries-for-alpine-linux/

EXPORT /go/bin/ /target

# run image
FROM alpine:latest
IMPORT /target/ /tmp
RUN cp /tmp/MailHog.o /MailHog
EXPOSE 1025 8025
CMD ["/MailHog"]
TAG mailhog/mailhog:{{ or .VERSION "latest" }}
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if we want to tag the build with version:

rocker build -var VERSION=x.y.z

the result will be a tagged image if you docker images.