**Improve database handling and disable redundant health checks**

- Added logic to construct `DATABASE_URL` from `DB_*` variables to prevent accidental fallback to SQLite during Docker Compose deployments.
- Updated `DATABASES` configuration to use `dj_database_url.parse` instead of deprecated `config`.
- Disabled health checks for services that do not expose a web port to avoid unnecessary probes.
- Removed unused `libmariadb-dev` and `pkg-config` dependencies from the `Dockerfile`.

Dockerfile

@@ -32,7 +32,7 @@ RUN . /etc/os-release \
     && echo "deb http://deb.debian.org/debian ${VERSION_CODENAME} non-free non-free-firmware" \
         > /etc/apt/sources.list.d/non-free.list \
     && apt update \
-    && apt install -y --no-install-recommends cron unrar libmariadb-dev pkg-config \
+    && apt install -y --no-install-recommends cron unrar \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /src

cbreader/settings/base.py

@@ -7,6 +7,7 @@ import os
 from datetime import timedelta
 from pathlib import Path
 from typing import Dict, List
+from urllib.parse import quote
 
 import dj_database_url
 from dotenv import load_dotenv
@@ -72,8 +73,19 @@ WSGI_APPLICATION = "cbreader.wsgi.application"
 
 DATABASE_URL = os.getenv("DATABASE_URL")
 
+# docker-compose passes DB_* variables, not a URL. Without building one from them the
+# app silently falls back to sqlite inside the container, and the web and cron
+# containers end up with two separate databases.
+if not DATABASE_URL and os.getenv("DB_HOST"):
+    DATABASE_URL = "postgres://{}:{}@{}/{}".format(
+        quote(os.getenv("DB_USER", "postgres"), safe=""),
+        quote(os.getenv("DB_PASS", ""), safe=""),
+        os.getenv("DB_HOST"),
+        os.getenv("DB_DATABASE", "postgres"),
+    )
+
 if DATABASE_URL:
-    DATABASES = {"default": dj_database_url.config(conn_max_age=500)}
+    DATABASES = {"default": dj_database_url.parse(DATABASE_URL, conn_max_age=500)}
 else:
     DATABASES = {"default": {"ENGINE": "django.db.backends.sqlite3", "NAME": os.path.join(BASE_DIR, "db.sqlite3")}}
 

compose/docker-compose.yml

@@ -30,6 +30,9 @@ services:
       - ${COMIC_BOOK_HOST_PATH}:${COMIC_BOOK_VOLUME}
       - media_files:/media
       - .env:/src/.env
+    # The image HEALTHCHECK probes the web port, which this service never serves.
+    healthcheck:
+      disable: true
     command: sh entrypoint-cron.sh
     restart: unless-stopped
 

docker-compose.yml

@@ -30,6 +30,9 @@ services:
       - ${COMIC_BOOK_HOST_PATH}:${COMIC_BOOK_VOLUME}
       - media_files:/media
       - .env:/src/.env
+    # The image HEALTHCHECK probes the web port, which this service never serves.
+    healthcheck:
+      disable: true
     command: sh entrypoint-cron.sh
     restart: unless-stopped