update kafka instructions for dealing with messages etc

dataflow/flex-templates/kafka_to_bigquery/README.md

@@ -130,9 +130,9 @@ For this, we need two parts running:
 > </details>
 
 The Kafka server must be accessible to *external* applications.
-For this we need a
-[static IP address](https://cloud.google.com/compute/docs/ip-addresses/reserve-static-external-ip-address)
-for the Kafka server to live.
+For this we need an
+[external static IP address](https://cloud.google.com/compute/docs/ip-addresses/reserve-static-external-ip-address)
+for the Kafka server to live. Not an internal IP address.
 
 > ℹ️ If you already have a Kafka server running you can skip this section.
 > Just make sure to store its IP address into an environment variable.
@@ -183,9 +183,21 @@ To learn more about pricing, see the
 ```sh
 export KAFKA_IMAGE="gcr.io/$PROJECT/samples/dataflow/kafka:latest"
 
+# Note: If the project name has `:` in it that signifies a project within an
+# organization (e.g. `example.com:project-id`), replace those with `/` so that
+# the Kafka image can be found appropriately.
+
 # Build the Kafka server image into Container Registry.
 gcloud builds submit --tag $KAFKA_IMAGE kafka/
 
+# If a different topic, address, kafka port, or zookeeper port is desired,
+# update the following environment variables before starting the server.
+# Otherwise, the default values will be used in the Dockerfile:
+export KAFKA_TOPIC=<topic-name>
+export KAFKA_ADDRESS=<kafka-address>
+export KAFKA_PORT=<kafka-port>
+export ZOOKEEPER_PORT=<zookeeper-port>
+
 # Create and start a new instance.
 # The --address flag binds the VM's address to the static address we created.
 # The --container-env KAFKA_ADDRESS is an environment variable passed to the
@@ -200,6 +212,70 @@ gcloud compute instances create-with-container kafka-vm \
   --tags "kafka-server"
 ```
 
+Note: The Kafka server should be running at this point, but in its current state
+no messages are being sent to a topic, which will cause the KafkaToBigQuery
+template to fail.
+
+
+### Sending messages to Kafka server
+
+SSH into the `kafka-vm` that was created earlier and issue
+the below commands that are required based on your timing. Messages sent before
+the template is started will be present when the template is started. If the 
+desire is to send messages after the template has started, then the messages
+will be processed as they are sent.
+
+Pre-Requisite SSH into the Kafka VM
+
+```sh
+$ gcloud compute ssh kafka-vm --zone "$ZONE"
+```
+
+1. Create a Topic
+
+```sh
+docker run --rm --network host bitnami/kafka:3.4.0 \
+/opt/bitnami/kafka/bin/kafka-topics.sh --bootstrap-server localhost:9092 \
+--create --topic <topic-name> --partitions 1 --replication-factor 1
+```
+
+2. Send Messages to the Topic
+
+Run the console producer to send messages. After running the command, type a
+message and press Enter. You can send multiple messages. Press Ctrl+C to stop
+the producer.
+
+Note: You can run this step either before starting the Dataflow template
+(messages will be ready) or while it's running (messages will be processed as
+they arrive).
+
+```sh
+docker run -i --rm --network host bitnami/kafka:3.4.0 \
+/opt/bitnami/kafka/bin/kafka-console-producer.sh \
+--bootstrap-server localhost:9092 --topic <topic-name>
+```
+
+3. (Optional) Verify the Messages
+
+You can check that your messages were sent correctly by starting a consumer.
+This will print all messages from the beginning of the topic. Press Ctrl+C to
+exit.
+
+```sh
+docker run -it --rm --network host bitnami/kafka:3.4.0 \
+/opt/bitnami/kafka/bin/kafka-console-consumer.sh \
+--bootstrap-server localhost:9092 --topic <topic-name> --from-beginning
+```
+
+4. (Optional) Delete a Topic
+
+```sh
+docker run --rm --network host bitnami/kafka:3.4.0 \
+/opt/bitnami/kafka/bin/kafka-topics.sh --bootstrap-server localhost:9092 \
+--delete --topic <topic-name>
+```
+
+
 ### Creating and running a Flex Template
 
 > <details><summary>
@@ -257,6 +333,21 @@ gcloud dataflow flex-template run "kafka-to-bigquery-`date +%Y%m%d-%H%M%S`" \
     --region "$REGION"
 ```
 
+Note: If one of the parameters is a deeply nested json or dictionary, use the
+gcloud `--flags-file` parameter to pass in a yaml file a list of all the
+parameters including the nested dictionary. Passing in the dictionary straight
+from the command line will give a gcloud error. The parameters file can look
+like this:
+
+```yaml
+--parameters:
+  inputTopic: messages
+  outputTable: $PROJECT:$DATASET.$TABLE
+  bootstrapServer: $KAFKA_ADDRESS:9092
+  schema:
+    '{type: object, properties: {processing_time: {type: TIMESTAMP}, url: {type: STRING}, rating: {type: STRING}}}'
+```
+
 Run the following query to check the results in BigQuery.
 
 ```sh

dataflow/flex-templates/kafka_to_bigquery/kafka/Dockerfile

@@ -24,7 +24,7 @@ ARG KAFKA_VERSION="2.4.0"
 ARG SCALA_VERSION="2.12"
 
 # Set variables with default values used by the `start-kafka.sh` script.
-# Override them wiht the `--env` or `-e` flag.
+# Override them with the `--env` or `-e` flag.
 # https://docs.docker.com/engine/reference/builder/#env
 ENV KAFKA_TOPIC="${KAFKA_TOPIC:-messages}"
 ENV KAFKA_ADDRESS="${KAFKA_ADDRESS:-localhost}"
@@ -33,7 +33,7 @@ ENV ZOOKEEPER_PORT="${ZOOKEEPER_PORT:-2181}"
 
 # Download and install Apache Kafka.
 RUN apk add --no-cache bash \
-  && wget http://apache.mirrors.spacedump.net/kafka/${KAFKA_VERSION}/kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz \
+  && wget https://archive.apache.org/dist/kafka/${KAFKA_VERSION}/kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz \
     -O /tmp/kafka.tgz \
   && tar xzf /tmp/kafka.tgz -C /opt && rm /tmp/kafka.tgz \
   && ln -s /opt/kafka_${SCALA_VERSION}-${KAFKA_VERSION} /opt/kafka