Introducing cloudemu

Think of a flight simulator. Pilots practice takeoffs, storms, and engine failures without ever leaving the ground — no fuel burned, no risk, no cost. cloudemu is a flight simulator for cloud software. It lets developers run and test their code as if it were talking to Amazon, Microsoft, or Google's cloud — except nothing real is being used, so it's instant and free.

The problem we set out to solve

Most modern apps rely on "the cloud" — services like storage, databases, and servers rented from Amazon (AWS), Microsoft (Azure), or Google (GCP). That's great for running an app, but it makes *testing* the app surprisingly painful. Today, teams have three choices, and each one hurts:

• Use the real cloud. Accurate, but it costs money, needs internet and accounts, and is slow — a few seconds per action adds up fast.
• Run a heavyweight local imitation. Tools exist, but they're clunky to set up and slow to start.
• Fake it by hand. Developers write throwaway stand-in code, but it's tedious, it drifts away from how the real cloud actually behaves, and every app has to be rewritten to use it.

None of these give you something that is fast, realistic, *and* free — and none let you test the exact code you plan to ship.

What cloudemu is

cloudemu is a small, free tool for developers building in the Go programming language. It pretends to be AWS, Azure, and Google Cloud, entirely inside your computer's memory. Your app thinks it's talking to the real cloud; in reality it's talking to cloudemu. Nothing leaves your machine.

The clever part: your app doesn't need to be changed to use it. Developers normally talk to the cloud through official "SDKs" — the standard code libraries each provider ships. cloudemu speaks the exact same language those SDKs use, so you point your app at cloudemu instead of the real cloud by changing a single line — the address. Everything else stays the same.

// The only change: point the client at cloudemu instead of real AWS.
client := s3.NewFromConfig(cfg, func(o *s3.Options) {
    o.BaseEndpoint = aws.String(cloudemuURL)
})

// This is your real, unchanged app code.
client.PutObject(ctx, &s3.PutObjectInput{ /* ... */ })

That's it. The same code you ship to production is the code you test.

Why it's better

And it doesn't just pretend at the surface. cloudemu mimics how the real services actually *behave* — the rules, the limits, the way things fail — so the tricky parts of an app get properly exercised before real users ever see them.

When to use it (and when not)

Use cloudemu when you want fast, reliable tests for cloud-connected code, when your automated checks need to run offline with no accounts, or when you want a free local "cloud" to build against.

Don't use it as a real cloud or a security tool. It's a practice environment — a stand-in for testing your own code, not a replacement for the real thing in production.

Get started

If you build in Go, you're one command away:

go get github.com/stackshy/cloudemu/v2

Point your app at cloudemu and run your existing tests. The Quick Start walks you through it in five minutes, and the documentation covers everything cloudemu supports across all three clouds.

We built cloudemu because testing cloud software should be fast, free, and painless. We hope it saves you as much time as it's saved us.

— Nitin Kumar Patel, Founder of CloudEmu