diff --git a/serving/samples/helloworld-rust/Dockerfile b/serving/samples/helloworld-rust/Dockerfile
index c3de829fb..84d3c30c1 100644
--- a/serving/samples/helloworld-rust/Dockerfile
+++ b/serving/samples/helloworld-rust/Dockerfile
@@ -1,10 +1,17 @@
+# 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 . .
 
+# Install production dependencies and build a release artifact.
 RUN cargo install
 
-EXPOSE 8080
+# Configure and document the service HTTP port.
+ENV PORT 8080
+EXPOSE $PORT
 
-CMD ["hellorust"]
\ No newline at end of file
+# 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 0a2030a0e..75faa7471 100644
--- a/serving/samples/helloworld-rust/README.md
+++ b/serving/samples/helloworld-rust/README.md
@@ -88,15 +88,22 @@ following instructions recreate the source files from this folder.
    block below into it.
 
     ```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 . .
 
+    # Install production dependencies and build a release artifact.
     RUN cargo install
 
-    EXPOSE 8080
+    # Configure and document the service HTTP port.
+    ENV PORT 8080
+    EXPOSE $PORT
 
+    # Run the web service on container startup.
     CMD ["hellorust"]
     ```