Deployment models for the Cloud Spanner emulator

This is the first of a three-part series of blog posts, which together will form a solution guide for developers using the Cloud Spanner emulator. In this series, after a quick introduction to the Cloud Spanner emulator, we will explore the usage of the emulator with a Cloud Spanner sample application called OmegaTrade.

We will manually deploy the OmegaTrade application’s backend service with a Cloud Spanner emulator backend instead of the Cloud Spanner instance and compare the pros and cons of running an emulator locally vs a remote GCE instance vs Cloud Run. But first, let’s talk about what the Cloud Spanner emulator is and how it can simplify your development process.

Overview

Cloud Spanner is a fully managed, distributed relational database offered on Google Cloud. Since its launch in 2017, Cloud Spanner has seen great interest and adoption, with customers from industries like gaming, retail, social media, and financial services running production workloads on Cloud Spanner. In addition to the recently-announced support for more granular instance sizing, which can be very handy for small or non-production workloads, Cloud Spanner offers a no-cost option that supports light-weight, offline environments, such as Continuous Integration and Continuous Delivery/Deployment (CI/CD).

This option is the Cloud Spanner emulator, which enables application developers to emulate an instance of Cloud Spanner locally for development and testing.

Introduction to the Cloud Spanner emulator

The Cloud Spanner emulator enables a no-cost experience for developers to quickly build and test applications with Cloud Spanner without the need for a GCP project, a billing account, or even an Internet connection. The emulator provides the same APIs as the Cloud Spanner production service with some limitations. An important thing to note is that the emulator is in-memory and does not persist data across restarts. All of the configuration, schema, and data are lost upon a restart.

The emulator is intended for local development and testing use cases – e.g., stand it up for a test suite with a known state, run the tests, verify its new state, then shut it down. It is also possible to deploy an emulator on a remote GCE instance and use it as a database for learning, development and testing purposes in a shared environment.

The Cloud Spanner emulator should not be used for performance testing and while the emulator can be used in development and test environments, it is still a good idea to verify your application by running it against the Cloud Spanner service before it is deployed to production.

• For a complete list of supported features and limitations of the emulator, take a look at the README file in GitHub.
• For a more detailed introduction to the Cloud Spanner emulator, read this post.

Running the Cloud Spanner emulator

There are multiple options available for running the emulator – a pre-built Docker image, pre-built Linux libraries, Bazel, or by building a custom Docker image. Below is a comparison between multiple ways of provisioning and starting the emulator and their respective use cases.