ERROR: Connection[1]: HTTP: Failed to switch protocols (response status = 400)
If you ever see this, there's a likely chance that your iOS or JavaScript Client is prevented from using WebSockets. Underneath the hood, Realm's sync protocol is built on top of WebSockets. So please consider that your setup can support WebSockets properly This is rarely an issue on most Android flavors.
WebSocket Compatibility Checklist
- If you are using AWS ELB version 1, make sure that you have TCP as the default setting
- If you are using AWS ELB version 2 is great!
- If you are using a proxy server, make sure that TCP is allowed
- In your Info.plist, make sure your App Transport Security (ATS) values are appropriately set, so that the operating system allows connecting to the domains. You can read more here about how to configure ATS https://developer.apple.com/library/content/releasenotes/General/WhatsNewIniOS/Articles/iOS9.html#App Transport Security