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Google Cloud Pub/Sub: Qwik Start - Python

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Google Cloud Pub/Sub: Qwik Start - Python

30 minutes 1 Credit

GSP094

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Overview

The Google Cloud Pub/Sub service allows applications to exchange messages reliably, quickly, and asynchronously. To accomplish this, a data producer publishes messages to a Cloud Pub/Sub topic. A subscriber client then creates a subscription to that topic and consumes messages from the subscription. Cloud Pub/Sub persists messages that could not be delivered reliably for up to seven days.

In this lab, you will learn how to get started publishing messages with Cloud Pub/Sub using the Python client library.

What you'll do

In this lab, you'll do the following:

  • Learn the basics of Pub/Sub.
  • Create and list a Pub/Sub topic.
  • Create and list a Pub/Sub subscription.
  • Publish messages to a topic.
  • Use a pull subscriber to output individual topic messages.

Setup and Requirements

Before you click the Start Lab button

Read these instructions. Labs are timed and you cannot pause them. The timer, which starts when you click Start Lab, shows how long Google Cloud resources will be made available to you.

This hands-on lab lets you do the lab activities yourself in a real cloud environment, not in a simulation or demo environment. It does so by giving you new, temporary credentials that you use to sign in and access Google Cloud for the duration of the lab.

To complete this lab, you need:

  • Access to a standard internet browser (Chrome browser recommended).
Note: Use an Incognito or private browser window to run this lab. This prevents any conflicts between your personal account and the Student account, which may cause extra charges incurred to your personal account.
  • Time to complete the lab---remember, once you start, you cannot pause a lab.
Note: If you already have your own personal Google Cloud account or project, do not use it for this lab to avoid extra charges to your account.

How to start your lab and sign in to the Google Cloud Console

  1. Click the Start Lab button. If you need to pay for the lab, a pop-up opens for you to select your payment method. On the left is the Lab Details panel with the following:

    • The Open Google Console button
    • Time remaining
    • The temporary credentials that you must use for this lab
    • Other information, if needed, to step through this lab
  2. Click Open Google Console. The lab spins up resources, and then opens another tab that shows the Sign in page.

    Tip: Arrange the tabs in separate windows, side-by-side.

    Note: If you see the Choose an account dialog, click Use Another Account.
  3. If necessary, copy the Username from the Lab Details panel and paste it into the Sign in dialog. Click Next.

  4. Copy the Password from the Lab Details panel and paste it into the Welcome dialog. Click Next.

    Important: You must use the credentials from the left panel. Do not use your Google Cloud Skills Boost credentials. Note: Using your own Google Cloud account for this lab may incur extra charges.
  5. Click through the subsequent pages:

    • Accept the terms and conditions.
    • Do not add recovery options or two-factor authentication (because this is a temporary account).
    • Do not sign up for free trials.

After a few moments, the Cloud Console opens in this tab.

Note: You can view the menu with a list of Google Cloud Products and Services by clicking the Navigation menu at the top-left. Navigation menu icon

Activate Cloud Shell

Cloud Shell is a virtual machine that is loaded with development tools. It offers a persistent 5GB home directory and runs on the Google Cloud. Cloud Shell provides command-line access to your Google Cloud resources.

  1. In the Cloud Console, in the top right toolbar, click the Activate Cloud Shell button.

Cloud Shell icon

  1. Click Continue.

It takes a few moments to provision and connect to the environment. When you are connected, you are already authenticated, and the project is set to your PROJECT_ID. The output contains a line that declares the PROJECT_ID for this session:

Your Cloud Platform project in this session is set to YOUR_PROJECT_ID

gcloud is the command-line tool for Google Cloud. It comes pre-installed on Cloud Shell and supports tab-completion.

  1. (Optional) You can list the active account name with this command:

gcloud auth list

(Output)

ACTIVE: * ACCOUNT: student-01-xxxxxxxxxxxx@qwiklabs.net To set the active account, run: $ gcloud config set account `ACCOUNT`
  1. (Optional) You can list the project ID with this command:

gcloud config list project

(Output)

[core] project = <project_ID>

(Example output)

[core] project = qwiklabs-gcp-44776a13dea667a6 For full documentation of gcloud, in Google Cloud, Cloud SDK documentation, see the gcloud command-line tool overview.

Create a virtual environment

Python virtual environments are used to isolate package installation from the system.

apt-get install -y virtualenv If prompted [Y/n], press Y and then Enter. If you get Permission denied error, then run the command sudo apt-get install -y virtualenv python3 -m venv venv

Activate the virtual environment.

source venv/bin/activate

Install the client library

Run the following to install the client library:

pip install --upgrade google-cloud-pubsub

Get the sample code by cloning a GitHub repository:

git clone https://github.com/googleapis/python-pubsub.git

Navigate to the directory:

cd python-pubsub/samples/snippets

Pub/Sub - the Basics

Google Cloud Pub/Sub is an asynchronous global messaging service. There are three terms in Pub/Sub that appear often: topics, publishing, and subscribing.

A topic is a shared string that allows applications to connect with one another through a common thread.

Publishers push (or publish) a message to a Cloud Pub/Sub topic. Subscribers will then make a subscription to that thread, where they will either pull messages from the topic or configure webhooks for push subscriptions. Every subscriber must acknowledge each message within a configurable window of time.

In sum, a publisher creates and sends messages to a topic and a subscriber creates a subscription to a topic to receive messages from it.

Pub/Sub in Google CLoud

Pub/Sub comes preinstalled in the Cloud Shell, so there are no installations or configurations required to get started with this service. In this lab you use Python to create the topic, subscriber, and then view the message. You use a gcloud command to publish the message to the topic.

Create a topic

To publish data to Cloud Pub/Sub you create a topic and then configure a publisher to the topic.

In Cloud Shell, your Project ID should automatically be stored in the environment variable GOOGLE_CLOUD_PROJECT:

echo $GOOGLE_CLOUD_PROJECT

Ensure the output is the same as the Project ID in your CONNECTION DETAILS.

publisher.py is a script that demonstrates how to perform basic operations on topics with the Cloud Pub/Sub API. View the content of publisher script:

cat publisher.py Note: Alternatively, you can use the shell editors that are installed on Cloud Shell, such as nano or vim or use the Cloud Shell code editor to view python-pubsub/samples/snippets/publisher.py

For information about the publisher script:

python publisher.py -h

Example Output, do not copy

usage: publisher.py [-h] project {list,create,delete,publish,publish-with-custom-attributes,publish-with-futures,publish-with-error-handler,publish-with-batch-settings} ... This application demonstrates how to perform basic operations on topics with the Cloud Pub/Sub API. For more information, see the README.md under /pubsub and the documentation at https://cloud.google.com/pubsub/docs. positional arguments: project Your Google Cloud project ID {list,create,delete,publish,publish-with-custom-attributes,publish-with-futures,publish-with-error-handler,publish-with-batch-settings} list Lists all Pub/Sub topics in the given project. create Create a new Pub/Sub topic. delete Deletes an existing Pub/Sub topic. publish Publishes multiple messages to a Pub/Sub topic. publish-with-custom-attributes Publishes multiple messages with custom attributes to a Pub/Sub topic. publish-with-futures Publishes multiple messages to a Pub/Sub topic and prints their message IDs. publish-with-error-handler Publishes multiple messages to a Pub/Sub topic with an error handler. publish-with-batch-settings Publishes multiple messages to a Pub/Sub topic with batch settings. optional arguments: -h, --help show this help message and exit

Run the publisher script to create Pub/Sub Topic:

python publisher.py $GOOGLE_CLOUD_PROJECT create MyTopic

Example Output, do not copy

Topic created: name: "projects/qwiklabs-gcp-fe27729bc161fb22/topics/MyTopic"

Test Completed Task

Click Check my progress to verify your performed task. If you have successfully created a Cloud Pub/Sub topic, you will see an assessment score.

Create a topic.

This command returns a list of all Pub/Sub topics in a given project:

python publisher.py $GOOGLE_CLOUD_PROJECT list

Example Output, do not copy

name: "projects/qwiklabs-gcp-fe27729bc161fb22/topics/MyTopic"

You can also view the topic you just made in the Cloud Console.

Navigate to Navigation menu > Pub/Sub > Topics.

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You should see MyTopic.

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Create a subscription

Create a Pub/Sub subscription for topic with subscriber.py script:

python subscriber.py $GOOGLE_CLOUD_PROJECT create MyTopic MySub

Test Completed Task

Click Check my progress to verify your performed task. If you have successfully created a Cloud Pub/Sub subscription, you will see an assessment score.

Create a subscription.

This command returns a list of subscribers in given project:

python subscriber.py $GOOGLE_CLOUD_PROJECT list-in-project

You'll see only one subscription because you've made only one subscription.

Example output (do not copy)

projects/qwiklabs-gcp-7877af129f04d8b3/subscriptions/MySub

Check out the subscription you just made in the console. In the left pane, click Subscriptions. You should see the subscription name and other details.

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For information about the subscriber script:

python subscriber.py -h

Output, do not copy

usage: subscriber.py [-h] project {list_in_topic,list_in_project,create,create-push,delete,update,receive,receive-custom-attributes,receive-flow-control,receive-synchronously,listen_for_errors} ... This application demonstrates how to perform basic operations on subscriptions with the Cloud Pub/Sub API. For more information, see the README.md under /pubsub and the documentation at https://cloud.google.com/pubsub/docs. positional arguments: project Your Google Cloud project ID {list_in_topic,list_in_project,create,create-push,delete,update,receive,receive-custom-attributes,receive-flow-control,receive-synchronously,listen_for_errors} list_in_topic Lists all subscriptions for a given topic. list_in_project Lists all subscriptions in the current project. create Create a new pull subscription on the given topic. create-push Create a new push subscription on the given topic. delete Deletes an existing Pub/Sub topic. update Updates an existing Pub/Sub subscription's push endpoint URL. Note that certain properties of a subscription, such as its topic, are not modifiable. receive Receives messages from a pull subscription. receive-custom-attributes Receives messages from a pull subscription. receive-flow-control Receives messages from a pull subscription with flow control. receive-synchronously Pulling messages synchronously. listen_for_errors Receives messages and catches errors from a pull subscription. optional arguments: -h, --help show this help message and exit

Publish messages

Now that you've set up MyTopic (the topic), a subscription to MyTopic (MySub), see if you can use gcloud commands to publish a message to MyTopic.

Publish the message "Hello" to MyTopic:

gcloud pubsub topics publish MyTopic --message "Hello"

Publish a few more messages to MyTopic—run the following commands (replacing <YOUR NAME> with your name and <FOOD> with a food you like to eat):

gcloud pubsub topics publish MyTopic --message "Publisher's name is <YOUR NAME>" gcloud pubsub topics publish MyTopic --message "Publisher likes to eat <FOOD>" gcloud pubsub topics publish MyTopic --message "Publisher thinks Pub/Sub is awesome"

View messages

Now that you've published messages to MyTopic, pull and view the messages using MySub.

Use MySub to pull the message from MyTopic:

python subscriber.py $GOOGLE_CLOUD_PROJECT receive MySub

Example output (do not copy)

Listening for messages on projects/qwiklabs-gcp-7877af129f04d8b3/subscriptions/MySub Received message: Message { data: 'Publisher thinks Pub/Sub is awesome' attributes: {} } Received message: Message { data: 'Hello' attributes: {} } Received message: Message { data: "Publisher's name is Harry" attributes: {} } Received message: Message { data: 'Publisher likes to eat cheese' attributes: {} }

Click Ctrl+c to stop listening.

Test your Understanding

Below are multiple-choice questions to reinforce your understanding of this lab's concepts. Answer them to the best of your abilities.

Congratulations!

You used the Python to create a Pub/Sub topic, published to the topic, created a subscription, then used the subscription to pull data from the topic.

completion_Baseline_Infrastructure-135.png

Finish Your Quest

This self-paced lab is part of the Baseline: Infrastructure. A Quest is a series of related labs that form a learning path. Completing this Quest earns you the badge above, to recognize your achievement. You can make your badge (or badges) public and link to them in your online resume or social media account. Enroll in this Quest and get immediate completion credit if you've taken this lab. See other available Quests.

Take Your Next Lab

  • Pub/Sub Lite: Qwik Start. Complementing Pub/Sub, Pub/Sub Lite is a zonal service for messaging systems with predictable traffic patterns. If you publish 1 MiB-1 GiB of messages per second, Pub/Sub Lite is a low cost option for high-volume event ingestion.

Next Steps /Learn More

  • This lab is part of a series of labs called Qwik Starts. These labs are designed to give you a little taste of the many features available with Google Cloud. Search for "Qwik Starts" in the lab catalog to find the next lab you'd like to take!

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Manual Last Updated February 28, 2022
Lab Last Tested February 28, 2022

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