Trigger function from Google Cloud Pub/Sub events¶

Trigger OpenFaaS functions from Google Cloud Pub/Sub messages.

Note: This feature is included for OpenFaaS Standard & For Enterprises

Installation¶

Setup the connector

You can install the Google Cloud Pub/Sub connector using its helm chart.

The values.yaml file can be customised to suit your needs.

Configure the connector for your needs by defining a values.yaml file

# Google cloud project ID
projectID: "openfaas-381517"

# List if Pub/Sub subscriptions the connector should subscribe to.
subscriptions:
  - my-sub

Use the subscriptions parameter to configure a list of Pub/Sub subscriptions to which the connector should subscribe. When the subscriber receives a message, the connector will attempt to invoke any function that has the subscription name listed in its topic annotation.

Usage¶

To test the connector, you can deploy the printer function. It prints out the HTTP headers and body of any invocation.

Add an annotation topic=sub1 so that the function is invoked for any message delivered to the sub1 Pub/Sub subscription.

Each time a function is invoked by the connector it will receive the message body as the HTTP body. Message attributes are mapped to HTTP Headers.

faas-cli store deploy printer \
  --annotation topic=sub1

Use the Google Cloud Console or gcloud CLI to publish a message for testing.

faas-cli logs printer

2025-04-02T11:40:50Z X-Pubsub-Attr-Foo=[Y]
2025-04-02T11:40:50Z X-Pubsub-Msg-Id=[14373415254515458]
2025-04-02T11:40:50Z User-Agent=[openfaas-gateway/0.4.39]
2025-04-02T11:40:50Z Accept-Encoding=[gzip]
2025-04-02T11:40:50Z X-Forwarded-For=[127.0.0.1:49964]
2025-04-02T11:40:50Z X-Topic=[my-sub]
2025-04-02T11:40:50Z X-Forwarded-Host=[127.0.0.1:8080]
2025-04-02T11:40:50Z X-Pubsub-Publish-Time=[2025-04-02T11:40:49Z]
2025-04-02T11:40:50Z X-Start-Time=[1743594050512199246]
2025-04-02T11:40:50Z Content-Type=[text/plain]
2025-04-02T11:40:50Z X-Call-Id=[f7fccd26-d8ee-4874-90e3-eefc94e2b74c]
2025-04-02T11:40:50Z X-Connector=[connector-sdk openfaasltd/gcp-pubsub-connector]
2025-04-02T11:40:50Z 
2025-04-02T11:40:50Z Hello OpenFaaS

Additional headers are made available to the request. These headers contain any message attributes along with some metadata about the Pub/Sub message.

X-PubSub-Msg-ID - the Pub/Sub message identifier.
X-PubSub-Publish-Time - the time at which the message was published.
X-PubSub-Delivery-Attempt - the number of times a message has been delivered.
X-PubSub-Ordering-Key - identifies related messages for which publish order should be respected.
X-PubSub-Attr-<key> - value of Pub/Sub message attribute.

So for example, if you added an attributed called Foo with a value of Y, you'd get the following extra header: X-PubSub-Attr-Foo: Y

The default content-type is configured as text/plain, but can be changed to another content-type such as application/json or application/octet-stream by the values.yaml file for the connector.

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