add docker multistage build #2

	name: run Docker CI

	on:
	push:
	branches:
	- main
	- master
	- add-docker-build
	pull_request:
	branches:
	- main
	- master

	env:
	CPM_SOURCE_CACHE: ${{ github.workspace }}/cpm_modules

	jobs:
	build:
	name: CI build docker
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v2

	#
	# configure and build in GitHub CI as smoke test

	# speed up configure step by installing boost as system lib, also use Ninja for faster builds
	- name: speed up configure and build
	shell: bash
	run: sudo apt-get update && sudo apt-get install -y libboost-all-dev ninja-build

	# use GitHub cache to cache dependencies
	- uses: actions/cache@v2
	with:
	path: "**/cpm_modules"
	key: ${{ github.workflow }}-cpm-modules-${{ hashFiles('/CMakeLists.txt', '/*.cmake') }}

	- name: configure
	run: cmake -S standalone -B build -G Ninja -D CMAKE_BUILD_TYPE=Release

	- name: build
	run: cmake --build build

	#
	# end GitHub CI local build

	- name: set up Docker Buildx for multi-platform support
	uses: docker/setup-buildx-action@v1

	- name: set up QEMU for multi-platform support
	uses: docker/setup-qemu-action@v1

	# build image but do NOT push to DockerHub
	- name: build Docker image
	uses: docker/build-push-action@v2
	with:
	file: ./standalone/Dockerfile
	platforms: linux/amd64,linux/arm64
	push: false
	tags: ${{ secrets.DOCKERHUB_USERNAME }}/greeter-webapi:ci
	cache-from: type=gha
	cache-to: type=gha,mode=max

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