Toy truck in the sand

Markus Spiske

Play in a sandbox in production

As an employed developer, you often have privileged access to the production environment of the application you’re working on. This is often required to do bug fixes or to run commands for folks in other departments of your organisation.

However, with great power comes a great ability to shoot yourself in the foot. It’s all too easy to make damaging changes to user data without meaning to.

Thankfully Rails gives us some nice protection, but you have to opt-in to using it.

Instead of…


$ heroku run rails console

…or similar.


…the sandbox flag when you spin up your Rails command line:

$ heroku run rails console --sandbox

You’ll see the following message before your IRB prompt as you log in:

Loading development environment in sandbox (Rails 7.0.6)
Any modifications you make will be rolled back on exit


Trust me, you don’t want to break real customer data in a permanent way. Make a habit of logging into production (and even staging) in sandbox mode.

When you exit the console in sandbox mode all the changes you’ve made to data will be rolled back. This should prevent you from doing anything catastrophic by accident. If you’re just querying data (read only) this mode will give you added reassurance you’re not going to permanently break anything.

You should be aware that if you’re calling code that enqueues jobs, perhaps using Sidekiq, or sends email, then that code will not be rolled back by the sandbox mechanism, so you should still be careful!

Why not?

If you’re logging into your production application to deliberately make changes to user data then you’ll need to avoid sandbox mode. However, I’d recommend seeing if you can test your changes in your sandbox before really executing them!

Additionally there’s a risk, which is expected behaviour of the feature, because of the way --sandbox is implemented, that you could lock rows or even whole tables for the rest of your regular production traffic. This is because this mode effectively puts everything in a transaction at the start of your session and rolls it back on logout, so even in sandbox mode you can break things. h/t to Will

In fact if you are making data changes in production it is better to write, test, and deploy code to make the required changes, rather than “wing it” in the console. Logging into production rails console should feel more scary than it does.

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Last updated on August 14th, 2023