Is there anything you or your community can do here - we would be more than happy to help out on an app that someone else owned but as Alex mentions, right now that wouldn’t be our focus.

Once we have the reference app out there, it should provide a significant infrastructure that people could use to rebuild the app with other web technologies if desired.

As Alex mentions, most app upgrades can be done easily today. Some particular types can present some difficult issues, but we have solutions for those - just not implemented yet. Since those kinds of upgrades are less common, we haven’t focused on building features to support those particular types of upgrades.

For Terracotta upgrades, the same is true. There are no fundamental or architectural issues at play here, we just haven’t to date focused on upward compatibility. There aren’t any real major technical issues, other than it is something we will focus on when we have to - for now we are highly focused on the other parts of the user experience(s) as Alex mentions.

I think the answer above depends on whether you are upgrading your app or Terracotta itself. With your own app, you can roll the upgrade through (assuming your shared data structures are not evolving much) without ever having a loss of service.

Upgrading Terracotta versions generally requires a full shutdown although there are some ways to partition your servers to even do that without a loss of service.