How to read Heroku build logs


Hi there,

I’m just starting out with everything and I’d like to know how exactly does one read the Heroku build logs? I finished my first app and it didn’t run on the last step (3.9). I followed advice in the forum to migrate again and all was well. There’s lots of ‘check the build logs for errors so I can tell you what’s wrong’ but can someone point me to some documentation on how to decipher it for myself?

Thanks in advance!


Do you mean how to view the logs or once you view them how to understand them?

To view them type heroku logs in the terminal when in the rails project directory.

To understand them takes time. As you use rails more and get to understand reading the server output as you build your app then the heroku logs are the same thing.



Thanks for replying. Seeking to understand. I see that it’s a lot of output and it of course will change based on the variables that I’ll have to learn to parse as I move along but there seem to be some constants that I am looking to understand. For instance why is the line with Heroku[router] orange (I thought that might have been pointing to an error at first, but is it just to make it stand out in the output)? Or what are all the sections of the first string, there’s clearly date and time but there’s also like maybe a MAC address? Is there anywhere to find out that kind of info in one place, or should I just keep swimming?

ALSO! While I have you, quick question, any idea why when I first ran the app and tried to open it in Heroku it didn’t work, but simply migrating it again did? If I didn’t change anything why was the result different the second time around?


Regarding the first question, just keep swimming. A lot of the information is just noise that you don’t really need to concern yourself with. You’ll learn what you need as you go.

Regarding the last question locally you use a development datebase and heroku is your platform database. They are kepy separate as during development you will create a lot of junk data to test stuff which you want to junk later. You would not want that data on a production database ever. So when you pushed to heroku it created a new empty production database. Therefore you needed to run the migrations to create the tables on your production database.