Googlecloud

+++ title = "Google Cloud Pub/Sub" description = "The fully-managed real-time messaging service from Google" date = 2019-07-06T22:30:00+02:00 bref = "The fully-managed real-time messaging service from Google" weight = 50 +++

Cloud Pub/Sub brings the flexibility and reliability of enterprise message-oriented middleware to the cloud.

At the same time, Cloud Pub/Sub is a scalable, durable event ingestion and delivery system that serves as a foundation for modern stream analytics pipelines. By providing many-to-many, asynchronous messaging that decouples senders and receivers, it allows for secure and highly available communication among independently written applications.

Cloud Pub/Sub delivers low-latency, durable messaging that helps developers quickly integrate systems hosted on the Google Cloud Platform and externally.

Official Documentation: https://cloud.google.com/pubsub/docs/

You can find a fully functional example with Google Cloud Pub/Sub in the Watermill examples.

Installation

go get github.com/ThreeDotsLabs/watermill-googlecloud/v2

Characteristics

Configuration

{{% load-snippet-partial file="src-link/watermill-googlecloud/pkg/googlecloud/publisher.go" first_line_contains="type PublisherConfig struct " last_line_contains="func NewPublisher" %}}

{{% load-snippet-partial file="src-link/watermill-googlecloud/pkg/googlecloud/subscriber.go" first_line_contains="type SubscriberConfig struct {" last_line_contains="func NewSubscriber(" %}}

Subscription name

To receive messages published to a topic, you must create a subscription to that topic. Only messages published to the topic after the subscription is created are available to subscriber applications.

The subscription connects the topic to a subscriber application that receives and processes messages published to the topic.

A topic can have multiple subscriptions, but a given subscription belongs to a single topic.

In Watermill, the subscription is created automatically during calling Subscribe(). Subscription name is generated by function passed to SubscriberConfig.GenerateSubscriptionName. By default, it is just the topic name (TopicSubscriptionName).

When you want to consume messages from a topic with multiple subscribers, you should use TopicSubscriptionNameWithSuffix or your custom function to generate the subscription name.

Connecting

Watermill will connect to the instance of Google Cloud Pub/Sub indicated by the environment variables. For production setup, set the GOOGLE_APPLICATION_CREDENTIALS env, as described in the official Google Cloud Pub/Sub docs. Note that you won't need to install the Cloud SDK, as Watermill will take care of the administrative tasks (creating topics/subscriptions) with the default settings and proper permissions.

For development, you can use a Docker image with the emulator and the PUBSUB_EMULATOR_HOST env ([check out the Getting Started guide]({{< ref "getting-started#subscribing_gcloud" >}})).

{{% load-snippet-partial file="src-link/_examples/pubsubs/googlecloud/main.go" first_line_contains="publisher, err :=" last_line_contains="panic(err)" padding_after="1" %}}

{{% load-snippet-partial file="src-link/_examples/pubsubs/googlecloud/main.go" first_line_contains="subscriber, err :=" last_line_contains="panic(err)" padding_after="1" %}}

Publishing

{{% load-snippet-partial file="src-link/watermill-googlecloud/pkg/googlecloud/publisher.go" first_line_contains="// Publish" last_line_contains="func (p *Publisher) Publish" %}}

Subscribing

{{% load-snippet-partial file="src-link/watermill-googlecloud/pkg/googlecloud/subscriber.go" first_line_contains="// Subscribe " last_line_contains="func (s *Subscriber) Subscribe" %}}

Marshaler

Watermill's messages cannot be directly sent to Google Cloud Pub/Sub - they need to be marshaled. You can implement your marshaler or use the default implementation.

{{% load-snippet-partial file="src-link/watermill-googlecloud/pkg/googlecloud/marshaler.go" first_line_contains="// Marshaler" last_line_contains="type DefaultMarshalerUnmarshaler " padding_after="0" %}}