Google PubSub component

A service that makes it easier to pass messages between machines and to collect data from IoT-devices.

---

Description

The component interacts with Google Pub-Sub API. The API is an asynchronous messaging service that decouples services that produce events from services that process events.

Pub/Sub offers durable message storage and real-time message delivery with high availability and consistent performance at scale. Pub/Sub servers run in all Google Cloud regions around the world.

Requirements

Core concepts

• Topic: A named resource to which messages are sent by publishers.
• Subscription: A named resource representing the stream of messages from a single, specific topic, to be delivered to the subscribing application. For more details about subscriptions and message delivery semantics, see the Subscriber Guide.
• Message: The combination of data and (optional) attributes that a publisher sends to a topic and is eventually delivered to subscribers.
• Message attribute: A key-value pair that a publisher can define for a message. For example, the key iana.org/language_tag and value en could be added to messages to mark them as readable by an English-speaking subscriber.

Credentials

Please Note : Google provides a JSON file that includes your private key. You should be careful how you are using the information. Follow the instructions below to succeed:

1. Copy and paste the private key as is.
2. Remove any line breakers (\n) from your key.
3. Leave the two lines as is with begin and end parts.

-----BEGIN PRIVATE KEY-----
YOUR KEY HERE
-----END PRIVATE KEY-----

How authentication works

PubSub component authentication works with Google IAM Service Accounts and two-legged OAuth, to authenticate your component you would need to create a new Service Account on Service Accounts Page of your project and download the JSON file with the private key. You would need client_email and private_key values on component authentication page (see here for more information).

Please Note : The authentication mechanism required access to the topics in your account to read and publish. If your created service account had no read permission (to subscribe as a trigger function) then verifications will fail. Save the credential without verification and use it for the publishing to the topics (as action function).

Permissions

To use the Subscribe trigger and Publish action make sure that your service account has all required permissions. Follow the screenshot below to succeed:

Triggers

Subscribe

The Subscribe trigger receives a message from a Topic, emits it, and sends an acknowledgment to Pub/Sub.

Configuration

• Select topic to subscribe - (dropdown, required): Select one of the available topics from the list.

Output Metadata

• data - (object or string, required): Data of the message, the component will try to parse it as JSON object if fails - result will be plain text.
• attributes - (object, optional): Attributes for this message - a list of "key": value pairs.
• id - (string, required): ID of this message, assigned by the server when the message is published.
• publishTime - (string, required): The time at which the message was published to Google Pub-Sub server.
• received - (string, required): The time at which the message was read by the component.

Limitations:

If you use ordinary flow (Real-time functionality is not enabled) after flow starts you will need to run it once (make execution) to create a subscription in Google Pub-Sub.

Deprecated Triggers

Actions

Publish

The Publish action retrieves the message body from a previous step and sends a message to a Topic while remaining unaware of any existing subscriptions.

Configuration

• Topic Name - (required field) fully-qualified topic resource name string, e.g. projects/<project_id>/topics/<topic_name>.

Warning

Please take special care of the independency of your processing flow, here is the extract from PubSub Subscriber Guide.

For the most part Pub/Sub delivers each message once, and in the order in which it was published. However, once-only and in-order delivery are not guaranteed: it may happen that a message is delivered more than once, and out of order. Therefore, your subscriber should be idempotent when processing messages, and, if necessary, able to handle messages received out of order. If ordering is important, we recommend that the publisher of the topic to which you subscribe include some kind of sequence information in the message; see this page for a full discussion on message ordering. Messages that are not acknowledged, are retried indefinitely for up to seven days.

Technical Notes

The technical notes page gives some technical details about Google PubSub component like changelog.