Update the serving Elixir example to freeze to 1.6 and to be compatible with Google Cloud Build (#461)

* Add an elixir language sample using the phoenix framework to the knative serving samples.

* Add links to Elixir and Phoenix Web sites.

* remove giant package-lock.json

* change -go to -elixir in readme.

* Update the Elixir example so that it builds with Google's Cloud Build service. Add an approprite .gcloudignore file so that this can be done using the gcloud command line tool.

Author: mikehelmick

serving/samples/helloworld-elixir/.gcloudignore

@@ -0,0 +1,24 @@
+# For building with Google Cloud Build using the gcloud command line tool.
+# Similar to .gitignore, except we want the /config/*.secrete.exs uploaded for the build.
+
+# App artifacts
+/_build
+/db
+/deps
+/*.ez
+
+# Generated on crash by the VM
+erl_crash.dump
+
+# Generated on crash by NPM
+npm-debug.log
+/assets/package-lock.json
+
+# Static artifacts
+/assets/node_modules
+
+# Since we are building assets from assets/,
+# we ignore priv/static. You may want to comment
+# this depending on your deployment strategy.
+/priv/static/
+

serving/samples/helloworld-elixir/Dockerfile

@@ -1,4 +1,5 @@
-FROM elixir:alpine
+FROM elixir:1.6.6-alpine
+
 ARG APP_NAME=hello
 ARG PHOENIX_SUBDIR=.
 ENV MIX_ENV=prod REPLACE_OS_VARS=true TERM=xterm
@@ -8,6 +9,7 @@ RUN apk update \
     && mix local.rebar --force \
     && mix local.hex --force
 COPY . .
+
 RUN mix do deps.get, deps.compile, compile
 RUN cd ${PHOENIX_SUBDIR}/assets \
     && npm install \
@@ -17,8 +19,18 @@ RUN cd ${PHOENIX_SUBDIR}/assets \
 RUN mix release --env=prod --verbose \
     && mv _build/prod/rel/${APP_NAME} /opt/release \
     && mv /opt/release/bin/${APP_NAME} /opt/release/bin/start_server
+
 FROM alpine:latest
 RUN apk update && apk --no-cache --update add bash openssl-dev
+
+RUN addgroup -g 1000 appuser && \
+    adduser -S -u 1000 -G appuser appuser
+
+RUN mkdir -p /opt/app/var
+RUN chown appuser /opt/app/var
+
+USER appuser
+
 ENV PORT=8080 MIX_ENV=prod REPLACE_OS_VARS=true
 WORKDIR /opt/app
 EXPOSE 8080

serving/samples/helloworld-elixir/README.md

@@ -38,15 +38,16 @@ Now you can visit [`localhost:4000`](http://localhost:4000) from your browser.
 
    ```docker
    # Start from a base image for elixir
-   FROM elixir:alpine
+   # Phoenix works best on pre 1.7 at the moment.
+   FROM elixir:1.6.6-alpine
 
    # Set up Elixir and Phoenix
    ARG APP_NAME=hello
    ARG PHOENIX_SUBDIR=.
    ENV MIX_ENV=prod REPLACE_OS_VARS=true TERM=xterm
    WORKDIR /opt/app
 
-   # Compile assets.
+   # Update nodejs, rebar, and hex.
    RUN apk update \
        && apk --no-cache --update add nodejs nodejs-npm \
        && mix local.rebar --force \
@@ -69,10 +70,19 @@ Now you can visit [`localhost:4000`](http://localhost:4000) from your browser.
    # Prepare final layer
    FROM alpine:latest
    RUN apk update && apk --no-cache --update add bash openssl-dev
-   ENV PORT=8080 MIX_ENV=prod REPLACE_OS_VARS=true
-   WORKDIR /opt/app
+
+   # Add a user so the server will run as a non-root user.
+   RUN addgroup -g 1000 appuser && \
+       adduser -S -u 1000 -G appuser appuser
+   # Pre-create necessary temp directory for erlang and set permissions.
+   RUN mkdir -p /opt/app/var
+   RUN chown appuser /opt/app/var
+   # Run everything else as 'appuser'
+   USER appuser
 
    # Document that the service listens on port 8080.
+   ENV PORT=8080 MIX_ENV=prod REPLACE_OS_VARS=true
+   WORKDIR /opt/app
    EXPOSE 8080
    COPY --from=0 /opt/release .
    ENV RUNNER_LOG_DIR /var/log