Add CircleCI configuration

Connects https://github.com/pelias/dockerfiles/issues/21

.circleci/config.yml

@@ -0,0 +1,12 @@
+version: 2
+jobs:
+  build:
+    working_directory: /app
+    docker:
+      - image: docker:17.05.0-ce-git
+    steps:
+      - checkout
+      - setup_remote_docker
+      - run:
+          name: Build and push image to Docker Hub
+          command: sh .circleci/docker.sh

.circleci/docker.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+set -u
+
+# collect params from ENV vars
+DATE=`date +%Y-%m-%d`
+DOCKER_REPOSITORY="pelias"
+DOCKER_PROJECT="${DOCKER_REPOSITORY}/${CIRCLE_PROJECT_REPONAME}"
+
+# the name of the image that represents the "branch", that is an image that will be updated over time with the git branch
+# the production branch is changed to "latest", otherwise the git branch becomes the name of the version
+if [[ "${CIRCLE_BRANCH}" == "production" ]]; then
+	DOCKER_BRANCH_IMAGE_VERSION="latest"
+else
+	DOCKER_BRANCH_IMAGE_VERSION="${CIRCLE_BRANCH}"
+fi
+DOCKER_BRANCH_IMAGE_NAME="${DOCKER_PROJECT}:${DOCKER_BRANCH_IMAGE_VERSION}"
+
+# the name of the image that represents the "tag", that is an image that is named with the date and git commit and will never be changed
+DOCKER_TAG_IMAGE_VERSION="${CIRCLE_BRANCH}-${DATE}-${CIRCLE_SHA1}"
+DOCKER_TAG_IMAGE_NAME="${DOCKER_PROJECT}:${DOCKER_TAG_IMAGE_VERSION}"
+
+# build image and login to docker hub
+docker build -t $DOCKER_PROJECT .
+docker login -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD"
+
+# copy the image to each of the two tags, and push
+docker tag $DOCKER_PROJECT $DOCKER_BRANCH_IMAGE_NAME
+docker tag $DOCKER_PROJECT $DOCKER_TAG_IMAGE_NAME
+docker push $DOCKER_BRANCH_IMAGE_NAME
+docker push $DOCKER_TAG_IMAGE_NAME