This document is intended to help you choose between Pub/Sub and Pub/Sub Lite. This document requires your familiarity with the basic concepts of Pub/Sub such as topics and subscriptions. If you are new to Pub/Sub, read What is Pub/Sub first.
Pub/Sub and Pub/Sub Lite are horizontally scalable and managed messaging services. These services can handle high volume and support large storage requirements. Pub/Sub is usually the default solution for most application integration and analytics use cases. It is feature-rich and fully managed. Pub/Sub Lite is recommended for applications where messaging throughput is more stable, workloads can benefit from a partition-based system, and cost is of a significant concern.
Pub/Sub offers a broader range of features, per-message parallelism, global routing, and automatically scaling resource capacity. In terms of message replication, Pub/Sub guarantees synchronous replication.
Pub/Sub Lite is a partition-based solution that trades off operational workload, global availability, and some features for cost efficiency. Pub/Sub Lite requires you to manually reserve and manage resource capacity. Within Pub/Sub Lite, you can choose zonal or regional Lite topics. Regional Lite topics offer the same availability SLA as Pub/Sub topics.
Note the reliability differences between the two services in terms of message replication. Pub/Sub supports synchronous data replication and uses three zones. Regional Lite topics replicate data to a secondary zone. Zonal Lite topics replicate data in only one zone.
Business requirements checklist
The following questions can help you choose the right Pub/Sub messaging service:
Are reliability, minimal operational cost, and ease of development your top priorities? Use Pub/Sub.
Are you willing to incur some additional operational overhead in terms of managing the topic capacity, can work with availability risks inherent to zonal services, and require low cost? Use zonal Lite topics.
Do you require some protection against zonal failures, are willing to incur an additional operational overhead in terms of managing the topic capacity, and require the lowest per throughput cost? Use regional Lite topics.
To know more about the cost differences between Pub/Sub and Pub/Sub Lite, see the pricing page.
Features comparison table
| Feature | Pub/Sub | Pub/Sub Lite |
|---|---|---|
| Access Transparency | Yes | No |
| Capacity | Automatically provisioned | Provision before you use |
| Client library languages | Java, Python, Go, Node.js, C++, C#, PHP, Ruby, SAP, ABAP | Java, Python, Go |
| Cross-project subscriptions | Yes | No |
| Customer managed encryption keys | Yes | No |
| Dead letter topics | Yes | No |
| Exactly-once delivery | Yes | No |
| Integrations | ||
| Message filtering | Yes for message attributes | No |
| Message replication | Yes | No |
| Message routing | Global | Zonal or regional |
| Message schema validation | Yes | No |
| Multi-zone in single region | No | Single zone or dual zone in a single region |
| Ordered delivery | Per-key ordering | Per-partition ordering |
| Message acknowledgment tracking | Per message | Per-partition cursor |
| Pricing | Pay for what you use | Pay for the capacity that you provision |
| REST endpoints | Yes | No |
| Resource namespace | Global | Zonal or regional |
| Retention period | Up to 31 days | Unlimited |
| Service endpoints | Global and regional | Regional |
| Storage | Unlimited | Unlimited |
| Subscription |
Data replication
Pub/Sub topics replicate data to three zones within a region. For more information about Pub/Sub data replication, see Data replication in a topic.
Regional Pub/Sub Lite topics replicate data to two zones within a region. Zonal Pub/Sub Lite topics store data in a single zone within a region. For more information about Pub/Sub Lite data replication, see Data replication in a Lite topic.
Message routing
Both Pub/Sub and Pub/Sub Lite can publish and subscribe from all regions, and even outside of Google Cloud.
Pub/Sub routes messages globally. Applications hosted in any region can publish messages to a single topic. The messages are processed in the nearest region permitted by your organization policies and forwarded to subscribers independently of the source.
Pub/Sub Lite routes messages within a region or a zone. Subscribers must connect to the instance of the service in the region where the topic is located. As a result, publishers and subscribers must maintain network connectivity to the same region to communication. Publishers can publish data to any topic from anywhere, but this may require connecting to a remote region, adding network latency. Subscribers that need aggregate data published to topics in different locations must connect to every relevant local service instance to read the messages.
Resource namespace
Pub/Sub topics and subscriptions are global resources. The Pub/Sub service can store messages in any region allowed by a topic storage policy. In addition, a topic and a subscription to that topic can be stored in different projects, allowing for fine-grained billing and access control. Finally, subscribers get the same data regardless of which service endpoint they use to connect to Pub/Sub or which service endpoint was used by the publisher of the data.
Zonal Lite topics and subscriptions are zonal resources. These resources must be in the same Cloud project and zone.
Regional Lite topics and subscriptions are regional resources. These resources must be in the same Cloud project and region.
For a list of regions and zones that Pub/Sub Lite supports, see Pub/Sub Lite locations.
Capacity management
Pub/Sub scales automatically. Capacity for message publishing is automatically provisioned, so you can send and receive message at any rate, up to the quotas you configure for your project.
Pub/Sub Lite is manually provisioned. You must configure the number of partitions per Lite topic. You must also provision storage and throughput capacity. Throughput capacity can be provisioned using Lite reservations.
Delivery Modes
Pub/Sub supports multiple message delivery modes. These include Pull (traditional polling), Push (HTTPS POST), StreamingPull (bidirectional RPC, for lowest latency and highest efficiency), and pull over HTTP REST and gRPC.
Pub/Sub Lite only supports streaming gRPC pull message delivery. To request messages, subscribers establish bidirectional streaming connections with each partition.
Parallelism
Pub/Sub uses per-message parallelism. This enables concurrent processing of any number of messages, from one or thousands of clients for a single subscription.
Pub/Sub Lite uses partition-based parallelism. This forces a client to process each data partition in linear order on a single client instance. This limits the maximum number of client instances to at most the number of partitions.
Streaming pipelines
Both Pub/Sub and Pub/Sub Lite are integrated with Dataflow for serverless stream processing and data integration. Pub/Sub allows Dataflow to scale more flexibly and supports Dataflow SQL.
To get started with Dataflow and Pub/Sub or Pub/Sub Lite, try these tutorials: