When the priv directory is deployed, it may not be in the same relative location as it is in project.

You can use :code.priv_dir with the name of your app as an argument to get the location of the priv dir after deployment and in your dev env.

iex(1)> :code.priv_dir(:blog)
~c"/home/chris/projects/blog/_build/dev/lib/blog/priv"