serving/samples: remove EXPOSE directive from helloworld (#644)

* serving/samples: remove EXPOSE directive from helloworld

* serving/samples: update ENV PORT comment for clarified purpose

* serving/samples: update README for Dockerfile changes

Author: grayside

serving/samples/helloworld-clojure/Dockerfile

@@ -13,9 +13,9 @@ COPY . .
 # Build an uberjar release artifact.
 RUN mv "$(lein uberjar | sed -n 's/^Created \(.*standalone\.jar\)/\1/p')" app-standalone.jar
 
-# Configure and document the service HTTP port.
+# Service must listen to $PORT environment variable.
+# This default value facilitates local development.
 ENV PORT 8080
-EXPOSE $PORT
 
 # Run the web service on container startup.
 CMD ["java", "-jar", "app-standalone.jar"]

serving/samples/helloworld-clojure/README.md

@@ -59,29 +59,29 @@ recreate the source files from this folder.
    see
    [the clojure image documentation](https://github.com/docker-library/docs/tree/master/clojure).
 
-   ```docker
-   # Use the official Clojure image.
-   # https://hub.docker.com/_/clojure
-   FROM clojure
+    ```docker
+    # Use the official Clojure image.
+    # https://hub.docker.com/_/clojure
+    FROM clojure
 
-   # Create the project and download dependencies.
-   WORKDIR /usr/src/app
-   COPY project.clj .
-   RUN lein deps
+    # Create the project and download dependencies.
+    WORKDIR /usr/src/app
+    COPY project.clj .
+    RUN lein deps
 
-   # Copy local code to the container image.
-   COPY . .
+    # Copy local code to the container image.
+    COPY . .
 
-   # Build an uberjar release artifact.
-   RUN mv "$(lein uberjar | sed -n 's/^Created \(.*standalone\.jar\)/\1/p')" app-standalone.jar
+    # Build an uberjar release artifact.
+    RUN mv "$(lein uberjar | sed -n 's/^Created \(.*standalone\.jar\)/\1/p')" app-standalone.jar
 
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
 
-   # Run the web service on container startup.
-   CMD ["java", "-jar", "app-standalone.jar"]
-   ```
+    # Run the web service on container startup.
+    CMD ["java", "-jar", "app-standalone.jar"]
+    ```
 
 1. Create a new file, `service.yaml` and copy the following service definition
    into the file. Make sure to replace `{username}` with your Docker Hub

serving/samples/helloworld-csharp/Dockerfile

@@ -14,9 +14,9 @@ COPY . .
 # Build a release artifact.
 RUN dotnet publish -c Release -o out
 
-# Configure and document the service HTTP port.
+# Service must listen to $PORT environment variable.
+# This default value facilitates local development.
 ENV PORT 8080
-EXPOSE $PORT
 
 # Run the web service on container startup.
 CMD ["dotnet", "out/helloworld-csharp.dll"]

serving/samples/helloworld-csharp/README.md

@@ -55,30 +55,30 @@ recreate the source files from this folder.
    app, see
    [dockerizing a .NET core app](https://docs.microsoft.com/en-us/dotnet/core/docker/docker-basics-dotnet-core#dockerize-the-net-core-application).
 
-   ```docker
-   # Use Microsoft's official .NET image.
-   # https://hub.docker.com/r/microsoft/dotnet
-   FROM microsoft/dotnet:2.1-sdk
-
-   # Install production dependencies.
-   # Copy csproj and restore as distinct layers.
-   WORKDIR /app
-   COPY *.csproj .
-   RUN dotnet restore
-
-   # Copy local code to the container image.
-   COPY . .
-
-   # Build a release artifact.
-   RUN dotnet publish -c Release -o out
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-
-   # Run the web service on container startup.
-   CMD ["dotnet", "out/helloworld-csharp.dll"]
-   ```
+    ```docker
+    # Use Microsoft's official .NET image.
+    # https://hub.docker.com/r/microsoft/dotnet
+    FROM microsoft/dotnet:2.1-sdk
+
+    # Install production dependencies.
+    # Copy csproj and restore as distinct layers.
+    WORKDIR /app
+    COPY *.csproj .
+    RUN dotnet restore
+
+    # Copy local code to the container image.
+    COPY . .
+
+    # Build a release artifact.
+    RUN dotnet publish -c Release -o out
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Run the web service on container startup.
+    CMD ["dotnet", "out/helloworld-csharp.dll"]
+    ```
 
 1. Create a new file, `service.yaml` and copy the following service definition
    into the file. Make sure to replace `{username}` with your Docker Hub

serving/samples/helloworld-dart/Dockerfile

@@ -2,6 +2,6 @@
 # https://hub.docker.com/r/google/dart-runtime/
 FROM google/dart-runtime
 
-# Configure and document the service HTTP port.
+# Service must listen to $PORT environment variable.
+# This default value facilitates local development.
 ENV PORT 8080
-EXPOSE $PORT

serving/samples/helloworld-dart/README.md

@@ -71,15 +71,15 @@ be created using the following instructions.
 4. Create a new file named `Dockerfile`, this file defines instructions for
    dockerizing your applications, for dart apps this can be done as follows:
 
-   ```Dockerfile
-   # Use Google's official Dart image.
-   # https://hub.docker.com/r/google/dart-runtime/
-   FROM google/dart-runtime
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-   ```
+    ```Dockerfile
+    # Use Google's official Dart image.
+    # https://hub.docker.com/r/google/dart-runtime/
+    FROM google/dart-runtime
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+    ```
 
 5. Create a new file, `service.yaml` and copy the following service definition
    into the file. Make sure to replace `{username}` with your Docker Hub

serving/samples/helloworld-elixir/Dockerfile

@@ -33,7 +33,6 @@ USER appuser
 
 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
 CMD ["/opt/app/bin/start_server", "foreground", "boot_var=/tmp"]

serving/samples/helloworld-elixir/README.md

@@ -84,7 +84,6 @@ When asked, if you want to `Fetch and install dependencies? [Yn]` select `y`
    # 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
 

serving/samples/helloworld-go/Dockerfile

@@ -19,9 +19,9 @@ FROM alpine
 # Copy the binary to the production image from the builder stage.
 COPY --from=builder /go/src/github.com/knative/docs/helloworld/helloworld /helloworld
 
-# Configure and document the service HTTP port.
+# Service must listen to $PORT environment variable.
+# This default value facilitates local development.
 ENV PORT 8080
-EXPOSE $PORT
 
 # Run the web service on container startup.
 CMD ["/helloworld"]

serving/samples/helloworld-go/README.md

@@ -80,9 +80,9 @@ recreate the source files from this folder.
    # Copy the binary to the production image from the builder stage.
    COPY --from=builder /go/src/github.com/knative/docs/helloworld/helloworld /helloworld
 
-   # Configure and document the service HTTP port.
+   # Service must listen to $PORT environment variable.
+   # This default value facilitates local development.
    ENV PORT 8080
-   EXPOSE $PORT
 
    # Run the web service on container startup.
    CMD ["/helloworld"]