Here’s a direct troubleshooting guide for “Docker 404 Not Found” on a DigitalOcean Droplet.

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Troubleshooting “Docker 404 Not Found” on DigitalOcean Droplet

1. The Root Cause

“Docker 404 Not Found” on a DigitalOcean Droplet typically indicates that while your Docker container is running and accessible on its exposed port, the application inside the container cannot locate the requested resource at the specified URL path. This usually stems from a misconfigured application path, an incorrect web server document root, or routing issues within the containerized application itself.

2. Quick Fix (CLI)

Perform these steps to quickly diagnose and potentially resolve the issue:

1. Inspect Container Logs: Check the application’s output for any startup errors, warnings related to paths, or explicit 404 messages from the application itself.

   docker logs <container_name_or_id>

2. Access Container Shell: Temporarily access the container’s shell to verify file paths, web server configurations, or the presence of expected resources.

   docker exec -it <container_name_or_id> bash # Use 'sh' if 'bash' is not available

   Once inside, navigate to expected web root directories (e.g., cd /var/www/html, cd /app) and list files (ls -la). Review web server configuration files (e.g., cat /etc/nginx/conf.d/default.conf for Nginx).

3. Restart Container: A simple restart can sometimes resolve transient application issues, especially if configuration changes were made inside the container.

   docker restart <container_name_or_id>

3. Configuration Check

The core of a “404 Not Found” error resides in the application’s or web server’s configuration within the Docker container.

1. Application Pathing/Routing:

   • Web Server Configuration: If your container runs a web server (e.g., Nginx, Apache), connect to the container via docker exec. Inspect configuration files (e.g., /etc/nginx/conf.d/*.conf, /etc/apache2/sites-available/*.conf). Verify the root or DocumentRoot directives, and location or Alias blocks, ensuring they point to the correct application directory or resource and are accessible within the container.
   • Application Framework Routing: For applications built with frameworks (Node.js, Python/Flask/Django, PHP/Laravel), review the application’s internal routing logic and base URL configuration. The application might be expecting a different base path than what’s being requested.

2. Dockerfile / docker-compose.yml (CMD/ENTRYPOINT):

   • Review the CMD or ENTRYPOINT instruction in your Dockerfile, or the command directive in your docker-compose.yml. Ensure this command correctly initiates your application and its web server processes. An incorrect startup command can lead to the application not serving content despite the container running.
   • If you’re using Docker volumes, verify that the host path mapped into the container exists and contains the expected application files.

4. Verification

After applying any configuration changes (rebuilding and restarting the container if Dockerfile or docker-compose.yml was modified, or restarting the application process within the container):

1. Local Droplet Verification: Execute curl from the Droplet’s terminal, targeting the container’s exposed port and the expected path. This bypasses external network issues.

   curl -v http://localhost:<host_port>/<expected_path>

   Replace <host_port> with the port mapped from your container (e.g., 80, 8080) and <expected_path> with the resource you expect to find (e.g., /index.html, /api/status). A successful response will show HTTP/1.1 200 OK.

2. Remote Access: If local verification is successful, attempt to access the application from your local machine via web browser or curl. Ensure your DigitalOcean Cloud Firewalls and any ufw rules on the Droplet itself allow traffic on <host_port>.

   curl -v http://<your_droplet_ip>:<host_port>/<expected_path>