Very occasionally the site goes into read only mode, seemingly due to high load. This isn’t usually a big deal, as it will usually resolve itself quite quickly.
However, if the user is in the middle of composing a post, an annoying thing happens. You get a modal dialog box that tells you that you’ve been logged out, and it asks you to Reload.
I would like to suggest that, instead of doing that, you just include a warning (likely in red) to the poster that their draft is not currently being saved (Or, better yet, temporarily save it locally), and to only report an error message if the user tries to actually submit their post.
I would also suggest the error message say that the site is in Read Only mode if that is the case, and tell the user to wait a bit and try posting again. And if the user needs to log back in, ask them to do so after submitting the post.
This would make for a much more smooth experience, and not force people to not be able to finish composing their post while the site is in read-only mode. Heck, for sites like ours where posters tend to take a long time to compose their posts, it’s likely that the site will be back in full by the time the poster finishes their post.