Myujth

I have been using pubsub for a bit of asynchronous work, and was wondering why someone may create multiple subscriptions for a single topic. My default values are as follows:

project_id = 'project'
topic_name = 'app'
subscription_name = 'general'

The routing of the actual function -- and how to process that -- is being doing in the subscriber receiver itself.

What would be reasons why there would be various subscription names? The only thing I can think of is to spread items across multiple servers for processing, such as:

server1 -- `main-1`
server2 -- `main-2`
etc.

Are there any other reasons why a subscription name would not work well with one value?

In general, there are two paradigms for having multiple subscribers:

1. Load balancing: The goal is to parallelize the processing of the load by having multiple subscribers using the same subscription. In this scenario, every subscriber receives a subset of the messages. One can horizontally scale processing by creating more subscribers for the same subscription.




2. Fan out: The goal is to have multiple subscribers receive the entire feed of messages. This is accomplished by having multiple subscriptions. The reason to have fan out is if there are multiple downstream applications interested in the full feed of messages. Imagine there is a feed where the messages are user events on a shopping website. Perhaps one application backs up the data to files, another analyzes the feed for trends in what people are looking at, and another looks through activity to try to find potentially fraudulent transactions. In this scenario, every one of those applications acting as a subscriber needs the full feed of messages, which requires separate subscriptions.