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Deltio

A Google Cloud Pub/Sub emulator alternative for local development.

ℹ️ DISCLAIMER: This project is not endorsed, sponsored, or affiliated with Google Cloud and/or the Rust Foundation.

Why?

Performance.

The official Google Cloud Pub/Sub emulator would make our machines come to a crawl under moderate load (for example, integration testing with >50 topics + subscriptions). Even after the tests were done, the emulator would still be spinning the CPU. Frequent restarts were needed, as performance degraded over time.

Deltio is a minimal implementation of a Google Cloud Pub/Sub emulator that supports the core features needed to use Pub/Sub.

Installation

You can either:

Running

When running outside of Docker (at least on macOS), it is recommended to increase the max open files limit to prevent the too many open files error.

$ ulimit -n unlimited

Assuming you have placed deltio somewhere in your $PATH, run Deltio with the default options (port: 8085):

$ deltio

To use a different port:

$ deltio --bind 0.0.0.0:1337

To see a list of options:

$ deltio --help

Limitations

As of this time, Deltio has very limited functionality, much less than the official Google Cloud Pub/Sub emulator.

Currently supported features:

  • Create topic
    • Only the name property is respected
  • Get topic
  • List topics in a project
  • Publish messages
    • Only the data and attributes properties are respected
  • Delete topics
  • Create subscription
    • Supports name and ack_deadline_seconds properties
  • Get subscription
  • List subscriptions in a project
  • List subscription names in a topic
  • Modify ACK deadlines
  • ACK messages
  • Pull messages
  • Streaming-pull messages
    • Including handling stream requests for acks and deadline modifications
    • Does NOT support flow control properties
  • Push subscriptions
    • No flow control
  • Message expiration
  • Deleting subscriptions

If something is not listed above, it's probably not supported yet. For example: message ordering, exactly-once delivery, deadletter and expiration policies, are not supported.

Compiling from source

Deltio is written in Rust, and requires a Protocol Buffers compiler. This is because the official Google Cloud Pub/Sub protos are used to generate the server code.

With both of those configured, you can simply run:

cargo build --release

What's in a name?

In Greek, the term "deltio" (δελτίο) translates to "bulletin" or "announcement." It is commonly used to refer to a document or publication that provides information, updates, or news about a particular topic. For example, a "deltio" can be a newsletter, a news bulletin, or an official communication issued by an organization or government entity.

~ ChatGPT

Author

Jeff Hansen - @Jeffijoe