protoc

This tool defines a custom build step that allows the Cloud Build worker to run the protocol buffer compiler, protoc.

When to use this builder

The gcr.io/cloud-builders/protoc build step should be used when you want to run protoc as part of your (Google Cloud) build process.

Building this builder

To build this builder and push the resulting image to the Container Registry in your project, run the following command in this directory:

$ gcloud builds submit . --config=cloudbuild.yaml

About the Dockerfile

The Docker file is where the protoc command is installed, and is the more complex of the two files:

FROM ubuntu

ARG PROTOC_VERSION=3.6.1
ARG PROTOC_TARGET=linux-x86_64
ARG ASSET_NAME=protoc-${PROTOC_VERSION}-${PROTOC_TARGET}.zip

RUN apt-get -qy update && apt-get -qy install python wget unzip && rm -rf /var/lib/apt/lists/*

RUN echo "${PROTOC_VERSION}/${ASSET_NAME}"

RUN wget https://github.com/google/protobuf/releases/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-${PROTOC_TARGET}.zip && \
unzip ${ASSET_NAME} -d protoc && rm ${ASSET_NAME}

ENV PATH=$PATH:/protoc/bin/
ENTRYPOINT ["protoc"]
CMD ["--help]

Breaking this down:

• Define the first read only layer of the final "protoc" image we want to end-up with. I chose Ubuntu because it's the what I run locally. Any minimal Linux "base image" will do but it must have the following binaries installed: apt-get, wget, unzip, and rm:

FROM ubuntu

• Set-up some variables that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag:

ARG PROTOC_VERSION=3.6.1 ARG PROTOC_TARGET=linux-x86_64 ARG ASSET_NAME=protoc-${PROTOC_VERSION}-${PROTOC_TARGET}.zip

• Run apt-get -qy update to "resynchronize the package index files from their sources". q omits progress indicators, y assumes yes as an answer to any prompts encountered:

RUN apt-get -qy update

• Install Python, Wget (retrieves content from web server), and Unzip.

RUN apt-get -qy install python wget unzip

• Remove any files created as part of the previous steps (and that are no longer needed):

RUN rm -rf /var/lib/apt/lists/*

The previous three RUN instructions can be combined into one:

RUN apt-get -qy update && apt-get -qy install python wget unzip && rm -rf /var/lib/apt/lists/*

• Use the ENV instruction to update the PATH environment to include the location of the protoc binary in the final environment (image).

ENV PATH=$PATH:/protoc/bin/

Set the ENTRYPOINT of the image such that the image runs as a protoc executable. Not, since the previous step added protoc to $PATH, we need only specify the binary to run (not the full path):

ENTRYPOINT ["protoc"]

• Use the CMD instruction so that if no options are provided when running the protoc image, protoc --help will run:

CMD ["--help]