Django on docker takes a lot of time to respond to any HTTP request immediately after launch – Debian

I’m running a dockerized Django application: only Django + Postgres on local.
When I start the application and go to any localhost URL, it takes up to 3-4 minutes to respond. Then it works as expected, with 100-200 ms response time.

• There are no heavy processes running and it behaves like that regardless of the URL, it could be admin, swagger or any other.
• It noticeably loads my CPU for the duration of that "freeze". I have had this issue for quite some time on a very old machine and thought it’s just because it’s old, but I’ve just tested it on a brand new one and it has the same issue, so it’s not the hardware.
• Deploy and URL/API tests are not affected by this and work with no freezes.
• Executing any commands with docker-compose exec or ~run works as expected despite the app not responding to any HTTP requests.

PS: I can add thread dump or any other logs if necessary, I really have no clue as to where to look for the source of the problem.

Here’s my .yml file contents, in case it might be the culprit:

version: '3'

volumes:
  backend_local_postgres_data: {}
  backend_local_postgres_data_backups: {}

services:
  django: &django
    build:
      context: .
      dockerfile: ./compose/local/django/Dockerfile
    image: backend_local_django
    container_name: backend_local_django
    depends_on:
      - postgres
    volumes:
      - .:/app:z
    env_file:
      - ./.envs/.local/.django
      - ./.envs/.local/.postgres
    ports:
      - "8000:8000"
    command: /start

  postgres:
    build:
      context: .
      dockerfile: ./compose/production/postgres/Dockerfile
    image: backend_production_postgres
    container_name: backend_local_postgres
    volumes:
      - backend_local_postgres_data:/var/lib/postgresql/data:Z
      - backend_local_postgres_data_backups:/backups:z
    env_file:
      - ./.envs/.local/.postgres

Application launch logs, as requested in a couple answers:

(venv) docker-compose -f local.yml up
[+] Running 1/1
 - Network backend_default  Created                                                                                                                                                                                          0.6s 
[+] Running 3/34T19:42:41+01:00" level=warning msg="mount of type `volume` should not define `bind` option"
 - Network backed_default            Created                                                                                                                                                                                0.6s
 - Container backend_local_postgres  Created                                                                                                                                                                                0.1s
 - Container backend_local_django    Created                                                                                                                                                                                0.1s
Attaching to backend_local_django, backend_local_postgres
| 
| PostgreSQL Database directory appears to contain a database; Skipping initialization
| 
| 2023-02-04 18:42:42.783 UTC [1] LOG:  starting PostgreSQL 14.6 (Debian 14.6-1.pgdg110+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit
| 2023-02-04 18:42:42.783 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
| 2023-02-04 18:42:42.783 UTC [1] LOG:  listening on IPv6 address "::", port 5432
| 2023-02-04 18:42:42.792 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
| 2023-02-04 18:42:42.804 UTC [27] LOG:  database system was shut down at 2023-02-01 11:55:22 UTC
| 2023-02-04 18:42:42.814 UTC [1] LOG:  database system is ready to accept connections
| PostgreSQL is available
| Operations to perform:
|   Apply all migrations: account, admin, auth, authtoken, constructor, contenttypes, django_celery_beat, sessions, sites, socialaccount, users
| Running migrations:      
|   No migrations to apply.
| WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
|  * Running on all addresses (0.0.0.0)
|  * Running on http://127.0.0.1:8000  
|  * Running on http://172.18.0.3:8000 
| Press CTRL+C to quit
|  * Restarting with watchdog (inotify)
| Performing system checks...
| 
| System check identified no issues (0 silenced).
| 
| Django version 4.0.8, using settings 'config.settings.local'
| Development server is running at http://0.0.0.0:8000/
| Using the Werkzeug debugger (http://werkzeug.pocoo.org/)
| Quit the server with CONTROL-C.
|  * Debugger is active!
|  * Debugger PIN: 130-235-671

In case the issue might be connected to one of the libraries I’m using, here’s my requirements.txt as well:

pytz==2022.6  # https://github.com/stub42/pytz
python-slugify==7.0.0  # https://github.com/un33k/python-slugify
Pillow==9.3.0  # https://github.com/python-pillow/Pillow
argon2-cffi==21.3.0  # https://github.com/hynek/argon2_cffi
redis==4.3.5  # https://github.com/redis/redis-py
hiredis==2.0.0  # https://github.com/redis/hiredis-py
celery==5.2.7  # pyup: < 6.0  # https://github.com/celery/celery
django-celery-beat==2.4.0  # https://github.com/celery/django-celery-beat
flower==1.2.0  # https://github.com/mher/flower

# Django
# ------------------------------------------------------------------------------
django==4.0.8  # pyup: < 4.1  # https://www.djangoproject.com/
django-environ==0.9.0  # https://github.com/joke2k/django-environ
django-model-utils==4.3.1  # https://github.com/jazzband/django-model-utils
django-allauth==0.51.0  # https://github.com/pennersr/django-allauth
django-crispy-forms==1.14.0  # https://github.com/django-crispy-forms/django-crispy-forms
crispy-bootstrap5==0.7  # https://github.com/django-crispy-forms/crispy-bootstrap5
django-redis==5.2.0  # https://github.com/jazzband/django-redis
# Django REST Framework
djangorestframework==3.14.0  # https://github.com/encode/django-rest-framework
django-cors-headers==3.13.0 # https://github.com/adamchainz/django-cors-headers
djangorestframework-simplejwt==5.2.2
drf-yasg==1.21.4

-r base.txt

Werkzeug[watchdog]==2.2.2 # https://github.com/pallets/werkzeug
ipdb==0.13.9  # https://github.com/gotcha/ipdb
psycopg2-binary==2.9.5  # https://github.com/psycopg/psycopg2
watchfiles==0.18.1  # https://github.com/samuelcolvin/watchfiles

# Testing
# ------------------------------------------------------------------------------
mypy==0.982  # https://github.com/python/mypy
django-stubs==1.12.0  # https://github.com/typeddjango/django-stubs
pytest==7.2.0  # https://github.com/pytest-dev/pytest
pytest-sugar==0.9.6  # https://github.com/Frozenball/pytest-sugar
djangorestframework-stubs==1.7.0  # https://github.com/typeddjango/djangorestframework-stubs

# Documentation
# ------------------------------------------------------------------------------
sphinx==5.3.0  # https://github.com/sphinx-doc/sphinx
sphinx-autobuild==2021.3.14 # https://github.com/GaretJax/sphinx-autobuild

# Code quality
# ------------------------------------------------------------------------------
flake8==5.0.4  # https://github.com/PyCQA/flake8
flake8-isort==5.0.3  # https://github.com/gforcada/flake8-isort
coverage==6.5.0  # https://github.com/nedbat/coveragepy
black==22.10.0  # https://github.com/psf/black
pylint-django==2.5.3  # https://github.com/PyCQA/pylint-django
pylint-celery==0.3  # https://github.com/PyCQA/pylint-celery
pre-commit==2.20.0  # https://github.com/pre-commit/pre-commit

# Django
# ------------------------------------------------------------------------------
factory-boy==3.2.1  # https://github.com/FactoryBoy/factory_boy

django-debug-toolbar==3.7.0  # https://github.com/jazzband/django-debug-toolbar
django-extensions==3.2.1  # https://github.com/django-extensions/django-extensions
django-coverage-plugin==2.0.4  # https://github.com/nedbat/django_coverage_plugin
pytest-django==4.5.2  # https://github.com/pytest-dev/pytest-django