diff --git a/serving/samples/helloworld-clojure/Dockerfile b/serving/samples/helloworld-clojure/Dockerfile
index 8b8e0894e41..ac1d66d5d40 100644
--- a/serving/samples/helloworld-clojure/Dockerfile
+++ b/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"]
diff --git a/serving/samples/helloworld-clojure/README.md b/serving/samples/helloworld-clojure/README.md
index 84c16133712..b92df6f664b 100644
--- a/serving/samples/helloworld-clojure/README.md
+++ b/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
diff --git a/serving/samples/helloworld-csharp/Dockerfile b/serving/samples/helloworld-csharp/Dockerfile
index 1bf2cab0b56..10dd884c4da 100644
--- a/serving/samples/helloworld-csharp/Dockerfile
+++ b/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"]
diff --git a/serving/samples/helloworld-csharp/README.md b/serving/samples/helloworld-csharp/README.md
index fe06d436c1e..dba6e3efdc1 100644
--- a/serving/samples/helloworld-csharp/README.md
+++ b/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
diff --git a/serving/samples/helloworld-dart/Dockerfile b/serving/samples/helloworld-dart/Dockerfile
index 6066d9c4d66..4d00aa6fbda 100644
--- a/serving/samples/helloworld-dart/Dockerfile
+++ b/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
diff --git a/serving/samples/helloworld-dart/README.md b/serving/samples/helloworld-dart/README.md
index 766ad1e3208..25de5a26150 100644
--- a/serving/samples/helloworld-dart/README.md
+++ b/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
diff --git a/serving/samples/helloworld-elixir/Dockerfile b/serving/samples/helloworld-elixir/Dockerfile
index fd5395a7614..37ae5ac71df 100644
--- a/serving/samples/helloworld-elixir/Dockerfile
+++ b/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"]
diff --git a/serving/samples/helloworld-elixir/README.md b/serving/samples/helloworld-elixir/README.md
index e567b9f265a..f078a76b3f6 100644
--- a/serving/samples/helloworld-elixir/README.md
+++ b/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
 
diff --git a/serving/samples/helloworld-go/Dockerfile b/serving/samples/helloworld-go/Dockerfile
index cc8b481c3e4..6e91928c31c 100644
--- a/serving/samples/helloworld-go/Dockerfile
+++ b/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"]
diff --git a/serving/samples/helloworld-go/README.md b/serving/samples/helloworld-go/README.md
index 607ce7f626c..b1b26d25767 100644
--- a/serving/samples/helloworld-go/README.md
+++ b/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"]
diff --git a/serving/samples/helloworld-haskell/Dockerfile b/serving/samples/helloworld-haskell/Dockerfile
index 3a5871619e5..ec479234c68 100644
--- a/serving/samples/helloworld-haskell/Dockerfile
+++ b/serving/samples/helloworld-haskell/Dockerfile
@@ -18,9 +18,9 @@ FROM fpco/haskell-scratch:integer-gmp
 WORKDIR /root/
 COPY --from=builder /root/.local/bin/helloworld-haskell-exe .
 
-# 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-haskell-exe"]
diff --git a/serving/samples/helloworld-haskell/README.md b/serving/samples/helloworld-haskell/README.md
index 84a6cefe998..c53bffdc6fc 100644
--- a/serving/samples/helloworld-haskell/README.md
+++ b/serving/samples/helloworld-haskell/README.md
@@ -80,34 +80,34 @@ recreate the source files from this folder.
 1. In your project directory, create a file named `Dockerfile` and copy the code
    block below into it.
 
-   ```docker
-   # Use the official Haskell image to create a build artifact.
-   # https://hub.docker.com/_/haskell/
-   FROM haskell:8.2.2 as builder
-
-   # Copy local code to the container image.
-   WORKDIR /app
-   COPY . .
-
-   # Build and test our code, then build the “helloworld-haskell-exe” executable.
-   RUN stack setup
-   RUN stack build --copy-bins
-
-   # Use a Docker multi-stage build to create a lean production image.
-   # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
-   FROM fpco/haskell-scratch:integer-gmp
-
-   # Copy the "helloworld-haskell-exe" executable from the builder stage to the production image.
-   WORKDIR /root/
-   COPY --from=builder /root/.local/bin/helloworld-haskell-exe .
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-
-   # Run the web service on container startup.
-   CMD ["./helloworld-haskell-exe"]
-   ```
+    ```docker
+    # Use the official Haskell image to create a build artifact.
+    # https://hub.docker.com/_/haskell/
+    FROM haskell:8.2.2 as builder
+
+    # Copy local code to the container image.
+    WORKDIR /app
+    COPY . .
+
+    # Build and test our code, then build the “helloworld-haskell-exe” executable.
+    RUN stack setup
+    RUN stack build --copy-bins
+
+    # Use a Docker multi-stage build to create a lean production image.
+    # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
+    FROM fpco/haskell-scratch:integer-gmp
+
+    # Copy the "helloworld-haskell-exe" executable from the builder stage to the production image.
+    WORKDIR /root/
+    COPY --from=builder /root/.local/bin/helloworld-haskell-exe .
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Run the web service on container startup.
+    CMD ["./helloworld-haskell-exe"]
+    ```
 
 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
diff --git a/serving/samples/helloworld-java/Dockerfile b/serving/samples/helloworld-java/Dockerfile
index 6e2290853d8..159b36e5f8c 100644
--- a/serving/samples/helloworld-java/Dockerfile
+++ b/serving/samples/helloworld-java/Dockerfile
@@ -18,10 +18,9 @@ FROM openjdk:8-jre-alpine
 # Copy the jar to the production image from the builder stage.
 COPY --from=builder /app/target/helloworld-*.jar /helloworld.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","-Djava.security.egd=file:/dev/./urandom","-Dserver.port=${PORT}","-jar","/helloworld.jar"]
-
diff --git a/serving/samples/helloworld-java/README.md b/serving/samples/helloworld-java/README.md
index ec5f67deedd..7935d58061d 100644
--- a/serving/samples/helloworld-java/README.md
+++ b/serving/samples/helloworld-java/README.md
@@ -86,34 +86,34 @@ recreate the source files from this folder.
    For additional information on multi-stage docker builds for Java see
    [Creating Smaller Java Image using Docker Multi-stage Build](http://blog.arungupta.me/smaller-java-image-docker-multi-stage-build/).
 
-   ```docker
-   # Use the official maven/Java 8 image to create a build artifact.
-   # https://hub.docker.com/_/maven
-   FROM maven:3.5-jdk-8-alpine as builder
-
-   # Copy local code to the container image.
-   WORKDIR /app
-   COPY pom.xml .
-   COPY src ./src
-
-   # Build a release artifact.
-   RUN mvn package -DskipTests
-
-   # Use the Official OpenJDK image for a lean production stage of our multi-stage build.
-   # https://hub.docker.com/_/openjdk
-   # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
-   FROM openjdk:8-jre-alpine
-
-   # Copy the jar to the production image from the builder stage.
-   COPY --from=builder /app/target/helloworld-*.jar /helloworld.jar
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-
-   # Run the web service on container startup.
-   CMD ["java","-Djava.security.egd=file:/dev/./urandom","-Dserver.port=${PORT}","-jar","/helloworld.jar"]
-   ```
+    ```docker
+    # Use the official maven/Java 8 image to create a build artifact.
+    # https://hub.docker.com/_/maven
+    FROM maven:3.5-jdk-8-alpine as builder
+
+    # Copy local code to the container image.
+    WORKDIR /app
+    COPY pom.xml .
+    COPY src ./src
+
+    # Build a release artifact.
+    RUN mvn package -DskipTests
+
+    # Use the Official OpenJDK image for a lean production stage of our multi-stage build.
+    # https://hub.docker.com/_/openjdk
+    # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
+    FROM openjdk:8-jre-alpine
+
+    # Copy the jar to the production image from the builder stage.
+    COPY --from=builder /app/target/helloworld-*.jar /helloworld.jar
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Run the web service on container startup.
+    CMD ["java","-Djava.security.egd=file:/dev/./urandom","-Dserver.port=${PORT}","-jar","/helloworld.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
diff --git a/serving/samples/helloworld-kotlin/Dockerfile b/serving/samples/helloworld-kotlin/Dockerfile
index 4eb2de019a7..69d23f8c2d1 100644
--- a/serving/samples/helloworld-kotlin/Dockerfile
+++ b/serving/samples/helloworld-kotlin/Dockerfile
@@ -17,9 +17,9 @@ FROM openjdk:8-jre-alpine
 # Copy the jar to the production image from the builder stage.
 COPY --from=builder /home/gradle/build/libs/gradle.jar /helloworld.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", "-Djava.security.egd=file:/dev/./urandom", "/helloworld.jar" ]
diff --git a/serving/samples/helloworld-kotlin/README.md b/serving/samples/helloworld-kotlin/README.md
index 34011446ad1..e73107babe2 100644
--- a/serving/samples/helloworld-kotlin/README.md
+++ b/serving/samples/helloworld-kotlin/README.md
@@ -108,33 +108,33 @@ recreate the source files from this folder.
 
 5. Create a file named `Dockerfile` and copy the code block below into it.
 
-   ```docker
-   # Use the official gradle image to create a build artifact.
-   # https://hub.docker.com/_/gradle
-   FROM gradle as builder
+    ```docker
+    # Use the official gradle image to create a build artifact.
+    # https://hub.docker.com/_/gradle
+    FROM gradle as builder
 
-   # Copy local code to the container image.
-   COPY build.gradle .
-   COPY src ./src
+    # Copy local code to the container image.
+    COPY build.gradle .
+    COPY src ./src
 
-   # Build a release artifact.
-   RUN gradle clean build --no-daemon
+    # Build a release artifact.
+    RUN gradle clean build --no-daemon
 
-   # Use the Official OpenJDK image for a lean production stage of our multi-stage build.
-   # https://hub.docker.com/_/openjdk
-   # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
-   FROM openjdk:8-jre-alpine
+    # Use the Official OpenJDK image for a lean production stage of our multi-stage build.
+    # https://hub.docker.com/_/openjdk
+    # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
+    FROM openjdk:8-jre-alpine
 
-   # Copy the jar to the production image from the builder stage.
-   COPY --from=builder /home/gradle/build/libs/gradle.jar /helloworld.jar
+    # Copy the jar to the production image from the builder stage.
+    COPY --from=builder /home/gradle/build/libs/gradle.jar /helloworld.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", "-Djava.security.egd=file:/dev/./urandom", "/helloworld.jar" ]
-   ```
+    # Run the web service on container startup.
+    CMD [ "java", "-jar", "-Djava.security.egd=file:/dev/./urandom", "/helloworld.jar" ]
+    ```
 
 6. Create a new file, `service.yaml` and copy the following service definition
    into the file. Make sure to replace `{username}` with your Docker Hub
diff --git a/serving/samples/helloworld-nodejs/Dockerfile b/serving/samples/helloworld-nodejs/Dockerfile
index 860bb4cfb52..91cf8742e3b 100644
--- a/serving/samples/helloworld-nodejs/Dockerfile
+++ b/serving/samples/helloworld-nodejs/Dockerfile
@@ -16,9 +16,9 @@ RUN npm install --only=production
 # Copy local code to the container image.
 COPY . .
 
-# 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 [ "npm", "start" ]
diff --git a/serving/samples/helloworld-nodejs/README.md b/serving/samples/helloworld-nodejs/README.md
index c83e95891a4..e0942618353 100644
--- a/serving/samples/helloworld-nodejs/README.md
+++ b/serving/samples/helloworld-nodejs/README.md
@@ -83,11 +83,12 @@ recreate the source files from this folder.
    see
    [Dockerizing a Node.js web app](https://nodejs.org/en/docs/guides/nodejs-docker-webapp/).
 
+
    ```Dockerfile
    # Use the official Node.js 10 image.
    # https://hub.docker.com/_/node
    FROM node:10
-
+   
    # Create and change to the app directory.
    WORKDIR /usr/src/app
 
@@ -102,9 +103,9 @@ recreate the source files from this folder.
    # Copy local code to the container image.
    COPY . .
 
-   # 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 [ "npm", "start" ]
diff --git a/serving/samples/helloworld-php/Dockerfile b/serving/samples/helloworld-php/Dockerfile
index 9c1f0b0d91b..7b95fe59a5e 100644
--- a/serving/samples/helloworld-php/Dockerfile
+++ b/serving/samples/helloworld-php/Dockerfile
@@ -14,6 +14,6 @@ RUN sed -i 's/80/${PORT}/g' /etc/apache2/sites-available/000-default.conf /etc/a
 # https://hub.docker.com/_/php#configuration
 RUN mv "$PHP_INI_DIR/php.ini-development" "$PHP_INI_DIR/php.ini"
 
-# 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
diff --git a/serving/samples/helloworld-php/README.md b/serving/samples/helloworld-php/README.md
index 7206e800d0c..09764000b8f 100644
--- a/serving/samples/helloworld-php/README.md
+++ b/serving/samples/helloworld-php/README.md
@@ -36,27 +36,27 @@ recreate the source files from this folder.
 1. Create a file named `Dockerfile` and copy the code block below into it. See
    [official PHP docker image](https://hub.docker.com/_/php/) for more details.
 
-   ```docker
-   # Use the official PHP 7.2 image.
-   # https://hub.docker.com/_/php
-   FROM php:7.2.6-apache
-
-   # Copy local code to the container image.
-   COPY index.php /var/www/html/
-
-   # Use the PORT environment variable in Apache configuration files.
-   RUN sed -i 's/80/${PORT}/g' /etc/apache2/sites-available/000-default.conf /etc/apache2/ports.conf
-
-   # Configure PHP for development.
-   # Switch to the production php.ini for production operations.
-   # RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini"
-   # https://hub.docker.com/_/php#configuration
-   RUN mv "$PHP_INI_DIR/php.ini-development" "$PHP_INI_DIR/php.ini"
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-   ```
+    ```docker
+    # Use the official PHP 7.2 image.
+    # https://hub.docker.com/_/php
+    FROM php:7.2.6-apache
+
+    # Copy local code to the container image.
+    COPY index.php /var/www/html/
+
+    # Use the PORT environment variable in Apache configuration files.
+    RUN sed -i 's/80/${PORT}/g' /etc/apache2/sites-available/000-default.conf /etc/apache2/ports.conf
+
+    # Configure PHP for development.
+    # Switch to the production php.ini for production operations.
+    # RUN mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini"
+    # https://hub.docker.com/_/php#configuration
+    RUN mv "$PHP_INI_DIR/php.ini-development" "$PHP_INI_DIR/php.ini"
+   
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+    ```
 
 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
diff --git a/serving/samples/helloworld-python/Dockerfile b/serving/samples/helloworld-python/Dockerfile
index 1875f5bdec8..e0bfa7b3118 100644
--- a/serving/samples/helloworld-python/Dockerfile
+++ b/serving/samples/helloworld-python/Dockerfile
@@ -10,9 +10,9 @@ COPY . .
 # Install production dependencies.
 RUN pip install Flask
 
-# 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 ["python", "app.py"]
diff --git a/serving/samples/helloworld-python/README.md b/serving/samples/helloworld-python/README.md
index 20582103907..03efd2219a0 100644
--- a/serving/samples/helloworld-python/README.md
+++ b/serving/samples/helloworld-python/README.md
@@ -47,26 +47,26 @@ recreate the source files from this folder.
    [official Python docker image](https://hub.docker.com/_/python/) for more
    details.
 
-   ```docker
-   # Use the official Python image.
-   # https://hub.docker.com/_/python
-   FROM python
-
-   # Copy local code to the container image.
-   ENV APP_HOME /app
-   WORKDIR $APP_HOME
-   COPY . .
-
-   # Install production dependencies.
-   RUN pip install Flask
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-
-   # Run the web service on container startup.
-   CMD ["python", "app.py"]
-   ```
+    ```docker
+    # Use the official Python image.
+    # https://hub.docker.com/_/python
+    FROM python
+
+    # Copy local code to the container image.
+    ENV APP_HOME /app
+    WORKDIR $APP_HOME
+    COPY . .
+
+    # Install production dependencies.
+    RUN pip install Flask
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Run the web service on container startup.
+    CMD ["python", "app.py"]
+    ```
 
 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
diff --git a/serving/samples/helloworld-ruby/Dockerfile b/serving/samples/helloworld-ruby/Dockerfile
index 7077135d8a8..c3114cb495f 100644
--- a/serving/samples/helloworld-ruby/Dockerfile
+++ b/serving/samples/helloworld-ruby/Dockerfile
@@ -11,9 +11,9 @@ RUN bundle install
 # Copy local code to the container image.
 COPY . .
 
-# 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 ["ruby", "./app.rb"]
diff --git a/serving/samples/helloworld-ruby/README.md b/serving/samples/helloworld-ruby/README.md
index 96e9116b123..2456f1cfd43 100644
--- a/serving/samples/helloworld-ruby/README.md
+++ b/serving/samples/helloworld-ruby/README.md
@@ -42,27 +42,27 @@ recreate the source files from this folder.
    [official Ruby docker image](https://hub.docker.com/_/ruby/) for more
    details.
 
-   ```docker
-   # Use the official Ruby image.
-   # https://hub.docker.com/_/ruby
-   FROM ruby:2.5
-
-   # Install production dependencies.
-   WORKDIR /usr/src/app
-   COPY Gemfile Gemfile.lock ./
-   ENV BUNDLE_FROZEN=true
-   RUN bundle install
-
-   # Copy local code to the container image.
-   COPY . .
-
-   # Configure and document the service HTTP port.
-   ENV PORT 8080
-   EXPOSE $PORT
-
-   # Run the web service on container startup.
-   CMD ["ruby", "./app.rb"]
-   ```
+    ```docker
+    # Use the official Ruby image.
+    # https://hub.docker.com/_/ruby
+    FROM ruby:2.5
+
+    # Install production dependencies.
+    WORKDIR /usr/src/app
+    COPY Gemfile Gemfile.lock ./
+    ENV BUNDLE_FROZEN=true
+    RUN bundle install
+
+    # Copy local code to the container image.
+    COPY . .
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Run the web service on container startup.
+    CMD ["ruby", "./app.rb"]
+    ```
 
 1. Create a file named `Gemfile` and copy the text block below into it.
 
diff --git a/serving/samples/helloworld-rust/Dockerfile b/serving/samples/helloworld-rust/Dockerfile
index 84d3c30c18e..10073fc6c2f 100644
--- a/serving/samples/helloworld-rust/Dockerfile
+++ b/serving/samples/helloworld-rust/Dockerfile
@@ -9,9 +9,9 @@ COPY . .
 # Install production dependencies and build a release artifact.
 RUN cargo install
 
-# 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 ["hellorust"]
diff --git a/serving/samples/helloworld-rust/README.md b/serving/samples/helloworld-rust/README.md
index 69b5a7312e7..6fa175cd7b7 100644
--- a/serving/samples/helloworld-rust/README.md
+++ b/serving/samples/helloworld-rust/README.md
@@ -87,25 +87,25 @@ recreate the source files from this folder.
 1. In your project directory, create a file named `Dockerfile` and copy the code
    block below into it.
 
-   ```docker
-   # Use the official Rust image.
-   # https://hub.docker.com/_/rust
-   FROM rust:1.27.0
+    ```docker
+    # Use the official Rust image.
+    # https://hub.docker.com/_/rust
+    FROM rust:1.27.0
 
-   # Copy local code to the container image.
-   WORKDIR /usr/src/app
-   COPY . .
+    # Copy local code to the container image.
+    WORKDIR /usr/src/app
+    COPY . .
 
-   # Install production dependencies and build a release artifact.
-   RUN cargo install
+    # Install production dependencies and build a release artifact.
+    RUN cargo install
 
-   # 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 ["hellorust"]
-   ```
+    # Run the web service on container startup.
+    CMD ["hellorust"]
+    ```
 
 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
diff --git a/serving/samples/helloworld-vertx/Dockerfile b/serving/samples/helloworld-vertx/Dockerfile
index 5bbee10eda9..0fe5bec6cb5 100644
--- a/serving/samples/helloworld-vertx/Dockerfile
+++ b/serving/samples/helloworld-vertx/Dockerfile
@@ -1,5 +1,11 @@
+# Use fabric8's s2i Builder image.
+# https://hub.docker.com/r/fabric8/s2i-java
 FROM fabric8/s2i-java:2.0
+
+# Service must listen to $PORT environment variable.
+# This default value facilitates local development.
+ENV PORT 8080
+
+# Copy the JAR file to the deployment directory.
 ENV JAVA_APP_DIR=/deployments
-EXPOSE 8080
 COPY target/helloworld-1.0.0-SNAPSHOT.jar /deployments/
-
diff --git a/serving/samples/helloworld-vertx/README.md b/serving/samples/helloworld-vertx/README.md
index 0ef5345b664..80220d51a79 100644
--- a/serving/samples/helloworld-vertx/README.md
+++ b/serving/samples/helloworld-vertx/README.md
@@ -143,12 +143,19 @@ To create and configure the source files in the root of your working directory:
 
 1. Create the `Dockerfile` file:
 
-   ```docker
-   FROM fabric8/s2i-java:2.0
-   ENV JAVA_APP_DIR=/deployments
-   EXPOSE 8080
-   COPY target/helloworld-1.0.0-SNAPSHOT.jar /deployments/
-   ```
+    ```docker
+    # Use fabric8's s2i Builder image.
+    # https://hub.docker.com/r/fabric8/s2i-java
+    FROM fabric8/s2i-java:2.0
+
+    # Service must listen to $PORT environment variable.
+    # This default value facilitates local development.
+    ENV PORT 8080
+
+    # Copy the JAR file to the deployment directory.
+    ENV JAVA_APP_DIR=/deployments
+    COPY target/helloworld-1.0.0-SNAPSHOT.jar /deployments/
+    ```
 
 1. Create the `service.yaml` file. You must specify your Docker Hub username in
    `{username}`. You can also configure the `TARGET`, for example you can modify