Most systems have multiple configuration profiles – one for production, one for development and often other profiles for staging, testing etc.  Minimising differences between these configurations is critical but there are inevitably some things that just have to be different. This then leaves the question, what should the default settings be?

There are three main options:

• Default to production values
• Default to development values
• Refuse to start unless an environment has been explicitly chosen

My preference is to default to development values. Why?

Development values should be “safe” in terms of any external integrations. So a developer isn’t going to accidentally start sending real buy or sell instructions to your stock broker.

There are more developers than production systems. If you default to production systems, every developer needs to remember to switch to development mode whenever they setup a new checkout. Defaulting to development mode means it just works for the most common case.

Checking authentication credentials for external systems into your source control system is generally considered a bad security practice, so the default values are unlikely to actually work in production anyway.

The down side with defaulting to development is it’s possible to accidentally deploy to production with development values causing an outage. This can be pretty easily prevented with automated deployments or using tools like RPM where files can be marked as config and thus avoid overwriting them when doing updates.

Refusing to start is the worst of all worlds – every developer has to specify a configuration mode and you still risk production outages by not specifying a mode.