Azure App Service allows you to host your application on a managed environment. You select the environment/stack (Java, PHP,ASP.net…) , Azure will setup the environment for you by using container , all you need is to deploy your code to this environment.
To deploy your code, Azure provides you some deployment tools: FTP/FTPS, Github, or local git. If you link your app with some tools like github,local git . This app service will automatically deploy your code when you commit your code (this can be turned off if you dont need)
All these app service is based on containers. you can provide your own image , if you use your own image, you need to manage your own deployment.
Since it’s based on container, whenever you restart the container, all the data will be lost except /home folder , /home is should where you keep all your permanent data.
You can add additional storage by mounting it to your storage account.
By default the App Service will be on public internet, it will not be able to connect to your on-prem service. To connect to onprem or limit access from internet you can setup some VPN endpoint. The other option is to use ASE v3.
App Service Environment v3 (ASE v3) is an isolated environment , we do not share resource with other clients. The App Service plan on this environment is more expensive than the general one. ASE v3 is free of charge for the setup, they charge the Web App you add to it.
If you want to you user own image, you need to either host it on dockerhub/ or your can use Azure Registry containers.