@Pierre Fleutot Following-up on this, it's great to hear that you are exploring Azure and planning to deploy a Symfony PHP app into App Services.
Based on my understanding of your scenario and as you have mentioned, the App Services database is not accessible from the internet.
You may connect to the app container directly from your local development machine using SSH, SFTP -New-SSH-Experience-and-Remote-Debugging-for-Linux-Web-Apps.html
You may try these steps to import a SQL file :
1. Open the Azure portal and navigate to your App Service web app.
2. Click on the "Configuration" tab and then click on "Connection strings".
3. Add a new connection string with the following details.
- Name: Any name you want to give to the connection string.
- Value: The connection string for your database. You can find this in the "Properties" section of your database server in the Azure portal.
- Type: Choose SQLServer".
4. Save the connection string.
5. Now, Under the "Development Tools" tab and click on "Advanced Tools".
6. Click on "Go" to open the Kudu console.
7. In the Kudu console, click on "Debug console" and then click on "CMD".
8. Navigate to the "site" folder and create a new folder called "data". (as required)
9. Upload your SQL file to the "data" folder via FTP
10. With an FTP client, you may copy files directly into /home/site/wwwroot
Reference: Can I use Secure Shell (SSH) to connect to the app container virtual machine (VM)?