Magento2 Developer Mode – How to Set Up

Most developers tend to immediately respond saying it is a bad thing to have developer mode turned on on a production server as if this is a true fact. I think this is different per situation/webshop.

What happens when you turn developer mode on?

1. mageCoreErrorHandler() will throw all errors instead of logging them
2. Magento will throw errors in certain situations where it would normally silently ignore this fault and continue
3. Mage::log() will always write to log even if logging is turned off
4. Exception printing will display the code trace on screen instead of showing an error report page
5. Other minor things in ignore skipping module updates, enterprise page cache, ....

Is this bad on a production server?

1. Your website visitors could end up will all sorts of gibberish which could confuse them and therefor could have a negative impact on your websites conversion
2. See no. 1
3. On a production server you would more likely have a lot more page views than on a testing server. This might mean that if you have logging turned on (or developer mode turned on) your logs could be flooded.
4. This is the one that could be harmful. If your exception traces get printed, then they can contain specific information that can be valuable to people with bad intentions.
5. ...

On these 5 points, I could say they depend highly on the situation of your live website. What is your audience? Do they get frightened and run away when seeing PHP exceptions and traces? How many page views does your site have? What information could be leaked with dumping backtraces?

When reading all of the above, one could generally say it is not advised to turn on developer mode on a production server "as a rule of thumb" ;).

But is it a 'bad thing' per se? ...

The default mode is neither here nor there.

The Magento team really wants you to use either Production Mode on your live site or Developer Mode during Development. The reason why Default Mode exists is to have something that would at least run reasonably when deployed directly from the downloaded code without further intervention.

By running php bin/magento deploy:mode:set you have identified yourself as capable and not needing the default mode. As there is no reason needing to go back to default mode Magento did not provide a way for you to do so.