Django Herokuへデプロイ後のアプリケーションエラーにつきまして

Question

前提・実現したいこと

DjangoのアプリをHerokuにデプロイしたのですが、アプリケーションエラーが出てしまいます。
何点かのエラーはスペルミスだったりと解決できたのですが、
下記のエラーについて、何が問題かわからず解決することができません。

解決策をご教授いただけませんでしょうか。
よろしくお願いいたします。

発生している問題・エラーメッセージ

2020-05-27T04:12:13.777912+00:00 app[web.1]: Arbiter(self).run()
（省略：10000文字以内でないと質問をアップできませんでしたので）
2020-05-27T04:12:26.493514+00:00 heroku[web.1]: State changed from starting to up
2020-05-27T04:12:27.151724+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [11] [ERROR] Exception in worker process
2020-05-27T04:12:27.151734+00:00 app[web.1]: Traceback (most recent call last):
2020-05-27T04:12:27.151736+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
2020-05-27T04:12:27.151737+00:00 app[web.1]: worker.init_process()
2020-05-27T04:12:27.151738+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 129, in init_process
2020-05-27T04:12:27.151738+00:00 app[web.1]: self.load_wsgi()
2020-05-27T04:12:27.151738+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 138, in load_wsgi
2020-05-27T04:12:27.151739+00:00 app[web.1]: self.wsgi = self.app.wsgi()
2020-05-27T04:12:27.151739+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/base.py", line 67, in wsgi
2020-05-27T04:12:27.151740+00:00 app[web.1]: self.callable = self.load()
2020-05-27T04:12:27.151740+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 52, in load
2020-05-27T04:12:27.151740+00:00 app[web.1]: return self.load_wsgiapp()
2020-05-27T04:12:27.151741+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 41, in load_wsgiapp
2020-05-27T04:12:27.151741+00:00 app[web.1]: return util.import_app(self.app_uri)
2020-05-27T04:12:27.151742+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/util.py", line 350, in import_app
2020-05-27T04:12:27.151742+00:00 app[web.1]: __import__(module)
2020-05-27T04:12:27.151743+00:00 app[web.1]: File "/app/limmiterproject/wsgi.py", line 16, in <module>
2020-05-27T04:12:27.151743+00:00 app[web.1]: application = get_wsgi_application()
2020-05-27T04:12:27.151743+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/core/wsgi.py", line 12, in get_wsgi_application
2020-05-27T04:12:27.151744+00:00 app[web.1]: django.setup(set_prefix=False)
2020-05-27T04:12:27.151744+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/__init__.py", line 19, in setup
2020-05-27T04:12:27.151745+00:00 app[web.1]: configure_logging(settings.LOGGING_CONFIG, settings.LOGGING)
2020-05-27T04:12:27.151745+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 79, in __getattr__
2020-05-27T04:12:27.151746+00:00 app[web.1]: self._setup(name)
2020-05-27T04:12:27.151746+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 66, in _setup
2020-05-27T04:12:27.151746+00:00 app[web.1]: self._wrapped = Settings(settings_module)
2020-05-27T04:12:27.151747+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 157, in __init__
2020-05-27T04:12:27.151747+00:00 app[web.1]: mod = importlib.import_module(self.SETTINGS_MODULE)
2020-05-27T04:12:27.151747+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/importlib/__init__.py", line 126, in import_module
2020-05-27T04:12:27.151748+00:00 app[web.1]: return _bootstrap._gcd_import(name[level:], package, level)
2020-05-27T04:12:27.151748+00:00 app[web.1]: File "/app/limmiterproject/settings.py", line 136, in <module>
2020-05-27T04:12:27.151749+00:00 app[web.1]: SECRET_KEY=os.environ['SECRET_KEY']
2020-05-27T04:12:27.151749+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/os.py", line 669, in __getitem__
2020-05-27T04:12:27.151750+00:00 app[web.1]: raise KeyError(key) from None
2020-05-27T04:12:27.151750+00:00 app[web.1]: KeyError: 'SECRET_KEY'
2020-05-27T04:12:27.152035+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [11] [INFO] Worker exiting (pid: 11)
2020-05-27T04:12:27.152514+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [10] [ERROR] Exception in worker process
2020-05-27T04:12:27.152514+00:00 app[web.1]: Traceback (most recent call last):
2020-05-27T04:12:27.152515+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
2020-05-27T04:12:27.152515+00:00 app[web.1]: worker.init_process()
2020-05-27T04:12:27.152515+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 129, in init_process
2020-05-27T04:12:27.152516+00:00 app[web.1]: self.load_wsgi()
2020-05-27T04:12:27.152516+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/workers/base.py", line 138, in load_wsgi
2020-05-27T04:12:27.152516+00:00 app[web.1]: self.wsgi = self.app.wsgi()
2020-05-27T04:12:27.152516+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/base.py", line 67, in wsgi
2020-05-27T04:12:27.152517+00:00 app[web.1]: self.callable = self.load()
2020-05-27T04:12:27.152517+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 52, in load
2020-05-27T04:12:27.152517+00:00 app[web.1]: return self.load_wsgiapp()
2020-05-27T04:12:27.152518+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/app/wsgiapp.py", line 41, in load_wsgiapp
2020-05-27T04:12:27.152518+00:00 app[web.1]: return util.import_app(self.app_uri)
2020-05-27T04:12:27.152518+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/gunicorn/util.py", line 350, in import_app
2020-05-27T04:12:27.152519+00:00 app[web.1]: __import__(module)
2020-05-27T04:12:27.152519+00:00 app[web.1]: File "/app/limmiterproject/wsgi.py", line 16, in <module>
2020-05-27T04:12:27.152519+00:00 app[web.1]: application = get_wsgi_application()
2020-05-27T04:12:27.152519+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/core/wsgi.py", line 12, in get_wsgi_application
2020-05-27T04:12:27.152519+00:00 app[web.1]: django.setup(set_prefix=False)
2020-05-27T04:12:27.152520+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/__init__.py", line 19, in setup
2020-05-27T04:12:27.152520+00:00 app[web.1]: configure_logging(settings.LOGGING_CONFIG, settings.LOGGING)
2020-05-27T04:12:27.152520+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 79, in __getattr__
2020-05-27T04:12:27.152520+00:00 app[web.1]: self._setup(name)
2020-05-27T04:12:27.152520+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 66, in _setup
2020-05-27T04:12:27.152521+00:00 app[web.1]: self._wrapped = Settings(settings_module)
2020-05-27T04:12:27.152521+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 157, in __init__
2020-05-27T04:12:27.152521+00:00 app[web.1]: mod = importlib.import_module(self.SETTINGS_MODULE)
2020-05-27T04:12:27.152521+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/importlib/__init__.py", line 126, in import_module
2020-05-27T04:12:27.152521+00:00 app[web.1]: return _bootstrap._gcd_import(name[level:], package, level)
2020-05-27T04:12:27.152522+00:00 app[web.1]: File "/app/limmiterproject/settings.py", line 136, in <module>
2020-05-27T04:12:27.152522+00:00 app[web.1]: SECRET_KEY=os.environ['SECRET_KEY']
2020-05-27T04:12:27.152522+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/os.py", line 669, in __getitem__
2020-05-27T04:12:27.152522+00:00 app[web.1]: raise KeyError(key) from None
2020-05-27T04:12:27.152525+00:00 app[web.1]: KeyError: 'SECRET_KEY'
2020-05-27T04:12:27.152868+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [10] [INFO] Worker exiting (pid: 10)
2020-05-27T04:12:27.305493+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [4] [INFO] Shutting down: Master
2020-05-27T04:12:27.305693+00:00 app[web.1]: [2020-05-27 04:12:27 +0000] [4] [INFO] Reason: Worker failed to boot.
2020-05-27T04:12:27.408007+00:00 heroku[web.1]: Process exited with status 3
2020-05-27T04:12:27.445441+00:00 heroku[web.1]: State changed from up to crashed
2020-05-27T04:13:52.438413+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=hidden-wave-**.herokuapp.com request_id=**-8b9e3ec70b68 fwd="111.239.161.15" dyno= connect= service= status=503 bytes= protocol=https

SECRET_KEYが原因なのか・・・とも思ったのですが、
settings.py と　local_settings.pyでは下記のように設定しており
自分では問題点をみつけることができませんでした。

settings.py

~省略〜

if not DEBUG:
    SECRET_KEY=os.environ.get('SECRET_KEY', "default_value") 
    import django_heroku 
    django_heroku.settings(locals()) 

try:
    from .local_settings import *
except ImportError:
    pass

~省略〜

local_settings.py

import os

BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))

SECRET_KEY = '******9x*************03*****' #settings.pyよりカット・ペースト

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}

DEBUG = True

Answer 1

django-environをインストールしていなかったことが原因でした。
下記の方法でデプロイできました。

インストール（pip install django-environ）
↓
requirements.txtを修正（pip freeze > requirements.txt）
↓
SECRET_KEYを環境変数に設定（Herokuのsettingsの画面で、Reveal Config Varsをクリックし
左のフォームにSECRET_KEY、右のフォームにSECRET_KEYの値を入力）