If you're experiencing a build issue during the deployment of your application, using Docker on your local machine, you can debug the issue further.

On your local machine:

1. Ensure you've installed Docker.

2. Go to the root of your application project and run:

docker run -it \
  -v $(pwd):/tmp/app gliderlabs/herokuish bash

3. You will now be running inside a Docker container that uses the Herokuish library, which is internally used by Dokku.

4. To see a list of current buildpacks, do:

herokuish buildpack list

5. To install an external buildpack, do:

herokuish buildpack install https://url-to-buildpack.git

6. Now test the build process by running:

herokuish test

If you encounter any errors and can't figure out next steps, please contact us. Some buildpacks might require the presence of environment variables to be set.