I’m guessing your AWS security group isn’t allowing tcp on port 80 or 8065.
Looks like the websocket cannot connect. Basically the http port used needs to be able to upgrade to a websocket connection (http:// -> ws://). If you’re using amazon ELB then you need to allow tcp port 80 to connect to tcp port 8065. If you configured with nginx then you need something like below in the nginx config.
proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection “upgrade”;
from https://github.com/mattermost/platform/blob/master/doc/install/Production-Ubuntu.md