Laravel+Inertia in docker container doesn't work

The error message:

All Inertia requests must receive a valid Inertia response, however a plain JSON response was received.

means that Inertia is expecting a special response header (X-Inertia) and/or a specific response structure, but is instead receiving a plain JSON response. This usually happens when:

• The request is not being routed through Laravel correctly (e.g., static file, wrong entrypoint, or misconfigured web server).
• The request is not hitting the Inertia controller as expected.
• There is a proxy or web server misconfiguration.

Given your setup, here are the most likely causes and solutions:

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1. Nginx Configuration

Problem:
If your Nginx is not configured to route all requests to public/index.php, then Inertia requests (especially those with Accept: application/json or X-Inertia headers) may not reach Laravel, and instead, Nginx may serve a static file or a default error response.

Solution:
Ensure your Nginx config includes the following (inside your server block):

location / {
    try_files $uri $uri/ /index.php?$query_string;
}

This ensures all requests (except for existing files) are routed to Laravel.

---

2. Trusted Proxies

Problem:
When running behind Caddy (reverse proxy) and Docker, Laravel may not correctly identify the original request headers (like X-Requested-With, X-Inertia, etc.) due to missing trusted proxy configuration.

Solution:
Set up trusted proxies in your App\Http\Middleware\TrustProxies:

protected $proxies = '*'; // or ['127.0.0.1', '::1'] for local docker

And ensure you have the correct headers:

protected $headers = Request::HEADER_X_FORWARDED_ALL;

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3. .env Configuration

Problem:
If APP_URL or SESSION_DOMAIN is not set correctly, Inertia requests may not be handled as expected.

Solution:
Check your .env:

APP_URL=https://demo-inertia.company.example
SESSION_DOMAIN=.company.example

---

4. Caddy Reverse Proxy

Problem:
Caddy may not be forwarding all headers, especially custom ones like X-Inertia.

Solution:
Caddy generally forwards all headers, but if you have custom header manipulation, ensure nothing is stripped.

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5. Volumes and File Permissions

Problem:
Your Docker volumes for storage may be causing permission issues or not mounting as expected, leading to unexpected errors.

Solution:
Double-check your volume mounts and permissions, especially for storage and logs.

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6. Debugging

Steps:

1. Check Nginx logs (logs/nginx) and Laravel logs (logs/application) for errors.
2. Inspect network requests in your browser dev tools. Check the response for Inertia requests—are they hitting Laravel? What is the response?
3. Add a test route in Laravel that returns an Inertia response and hit it directly.

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Summary Checklist

• Nginx config uses try_files $uri $uri/ /index.php?$query_string;
• Laravel trusted proxies are set (TrustProxies middleware)
• .env has correct APP_URL and SESSION_DOMAIN
• Caddy is not stripping headers
• Docker volumes and permissions are correct

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Example Nginx Config

Here’s a minimal example for your Nginx container:

server {
    listen 80;
    server_name _;

    root /var/www/public;

    index index.php index.html;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location ~ \.php$ {
        fastcgi_pass app:9000;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        include fastcgi_params;
    }

    location ~ /\.ht {
        deny all;
    }
}

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If you update your Nginx config as above and ensure trusted proxies are set, your Inertia requests should work as expected inside Docker.