[MatthewPhillips]

Don't attempt to build a SPA if you are support browsers that old (even IE8 imo). Give them a traditional server-rendered app and they'll be happy.

Since you've already built with React, the good news is that it's easy to build a React app that you deploy as a server-rendered app. Just make sure you are doing things in normal HTML, like forms, and not relying on xhr/fetch.

[brudgers]

Being on premises even mitigates two of the major tradeoffs with server side rendering, latency and matching demand to computational power and bandwidth.