SharePoint Online Add In Apps
The path Microsoft wish for developers to take is creating SharePoint add in apps. These can be developed and delivered in multiple ways depending of the requirement of the solution. A “SharePoint hosted Add In” is exactly what it says on the tin. You can create an Add in app and host it on your own SharePoint site. The limitation of this is you cannot use server side code such as C#. Instead your solution must be written in client side code such as Javascript.
This can have multiple drawbacks for developers so there is another option referred to as “Provider hosted Add in app”. These are applications that run in a server that is external to SharePoint’s.
That server would have its own infrastructure and the “Provider” would be responsible for keeping it running smoothly. A provider hosted Add in app allows developers to use server side code using the .NET CSOM. This is the method we usually find best for meeting the requirements of the App.
Migration To Currently Used SharePoint Site
You may have been using a hybrid structure up to now, but considering moving everything to SharePoint Online. This can be achieved but requires a slightly different approach to the migration planning.
The migration plan will include merging content from your on-prem to existing content on SharePoint online. This requires consideration of how the site structure will be set up to make navigation easy for your end users.
Before migrating be aware of existing content on the SharePoint online site such as workflows and how your migration may impact on it.
I had made a mistake when I was first trialing migration software last year. I was copying content from my on-prem dev environment to my SharePoint online dev site. The mistake happened when I migrated 300 list items to an existing list which an alert workflow had been set up. It then issued me 300 alert emails.
This is the type of scenario to consider to make sure your migration does not conflict with existing content.