Hi everyone.
I configured Mattermost and Apache2 proxy, according to your instructions (thanks!). Everything is working just fine, exept of one thing: When a user joins new channel, or is switching between channels, before she or he can write messages - channel is reloading (sometimes one time, sometinmes few times) with messages replaced by "Loading...". It is quite annoying.
There was no such problem, when there was no proxying through Apache, just nginx with mattermost, so I think it is issue connected with Apache proxying. Maybe someone had similar problem and can help?