Introduction
I'm currently writing a generic script to automatically cache stages for a multi stage dockerfile
The way I envision it to work is to automatically go through a dockerfile, find all the different stages (basically search for FROM .... AS ... Once the code finds this, I can then do a docker build where I tag this specific stage as something like imagename-stage:firststage.
However as the documentation describes you can also have multi-stage docker files without a name: https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
Example:
FROM golang:1.7.3
WORKDIR /go/src/github.com/alexellis/href-counter/
RUN go get -d -v golang.org/x/net/html
COPY app.go .
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .
FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY --from=0 /go/src/github.com/alexellis/href-counter/app .
CMD ["./app"]
In the example above you refer to the previous stage by adding --from=0
Problem
When i try to target the first stage in a dockerfile that contains no AS ... I would expect I could do something like:
docker build . --target 0
However when i do this, I get the following error:
Sending build context to Docker daemon 49.99MB
Error response from daemon: failed to reach build target 0 in Dockerfile
Does someone know how to resolve this?
Edit:
I also posted this question on the docker forum, but so far I haven't seen a response: https://forums.docker.com/t/docker-build-first-stage-in-multi-stage-pipeline/91167