Google Cloud Pub/Sub

Synopsis

Creates a subscriber that connects to a Google Cloud Pub/Sub subscription and consumes messages using concurrent goroutine receivers. Supports Application Default Credentials and explicit service account credentials.

Schema

- id: <numeric>
  name: <string>
  description: <string>
  type: pubsub
  tags: <string[]>
  pipelines: <pipeline[]>
  status: <boolean>
  properties:
    project_id: <string>
    subscription_id: <string>
    credentials_json: <string>
    workers: <numeric>
    max_outstanding_messages: <numeric>
    max_outstanding_bytes: <numeric>

Configuration

Device

Field	Required	Default	Description
id	Y	-	Unique numeric identifier
name	Y	-	Device name
description	N	-	Optional description
type	Y	-	Must be pubsub
tags	N	-	Optional tags
pipelines	N	-	Optional pre-processor pipelines
status	N	true	Enable/disable the device

Connection

Field	Required	Default	Description
project_id	Y		Google Cloud project ID
subscription_id	Y		Pub/Sub subscription name
credentials_json	N	-	Service account credentials JSON. When omitted, Application Default Credentials are used

Performance

Field	Required	Default	Description
workers	N	0	Number of goroutines for concurrent message processing. 0 defaults to GOMAXPROCS
max_outstanding_messages	N	1000	Maximum number of unprocessed messages held in memory at once
max_outstanding_bytes	N	1000000000	Maximum total byte size of unprocessed messages held in memory at once (1 GB)

Details

The device connects to a single Pub/Sub subscription and opens a long-lived streaming pull connection. Message delivery uses the Google Cloud Pub/Sub SDK's Receive method, which dispatches the callback concurrently from multiple goroutines controlled by the workers setting. A mutex serializes all writes to the internal stream writers, so concurrent callbacks do not overwrite each other's data.

Messages are acknowledged after a successful write. If the write fails, the message is negatively acknowledged and redelivered. Empty payloads are acknowledged immediately without processing to prevent infinite redelivery loops.

The workers field controls the number of concurrent goroutine receivers within a single Receive call. This is the correct scaling mechanism for Pub/Sub throughput: multiple Receive calls on the same subscription compete for the same messages rather than parallelizing work, whereas increasing workers lets a single subscriber drain faster.

The max_outstanding_messages and max_outstanding_bytes limits cap how many messages are held in memory concurrently, bounding memory consumption under burst conditions. Setting these values too high can cause out-of-memory errors during traffic spikes.

When credentials_json is omitted, the SDK resolves credentials using Application Default Credentials, which includes Workload Identity Federation on GKE and other Google-managed environments. When running outside Google Cloud, a service account key JSON must be supplied explicitly.

The subscription must already exist in the specified project. The device validates both project_id and subscription_id at startup and will not start if either is missing or empty. The connection state is set to connected once the consumer is successfully created.

Examples

Basic

Creating a basic Pub/Sub subscriber using Application Default Credentials...

- id: 1 name: pubsub_basic type: pubsub properties: project_id: "my-gcp-project" subscription_id: "my-subscription"

Service Account

Connecting with an explicit service account key...

- id: 2 name: pubsub_service_account type: pubsub properties: project_id: "my-gcp-project" subscription_id: "my-subscription" credentials_json: | { "type": "service_account", "project_id": "my-gcp-project", "private_key_id": "key-id", "private_key": "-----BEGIN RSA PRIVATE KEY-----\n...\n-----END RSA PRIVATE KEY-----\n", "client_email": "datastream@my-gcp-project.iam.gserviceaccount.com", "client_id": "123456789", "auth_uri": "https://accounts.google.com/o/oauth2/auth", "token_uri": "https://oauth2.googleapis.com/token" }

High-Volume

Optimizing for high-throughput message consumption...

- id: 3 name: pubsub_high_volume type: pubsub properties: project_id: "my-gcp-project" subscription_id: "high-volume-subscription" workers: 16 max_outstanding_messages: 5000 max_outstanding_bytes: 2000000000

note

Setting max_outstanding_bytes above available memory can cause out-of-memory errors during traffic bursts.

Pipeline Processing

Applying custom processing to Pub/Sub messages...

- id: 4 name: pubsub_pipeline type: pubsub pipelines: - json_parser - field_extractor properties: project_id: "my-gcp-project" subscription_id: "structured-logs"

note

Pipelines are processed sequentially and can modify or drop messages before ingestion.

Memory-Constrained

Limiting memory usage in resource-constrained deployments...

- id: 5 name: pubsub_low_memory type: pubsub properties: project_id: "my-gcp-project" subscription_id: "my-subscription" workers: 2 max_outstanding_messages: 100 max_outstanding_bytes: 10000000