You could regenerate the start page every 5s and comment pages whenever you need (new, edited or deleted comments) or every request if there has been more than

You could regenerate the start page every 5s and comment pages whenever you need (new, edited or deleted comments) or every request if there has been more than 30s since it was last updated. That would leave the serving to some of the applications being good at that (varnish?). Finding the right heuristic regarding page regeneration might take some tweaking, but the amount of generating you have to do is small enough not to bother any single threaded program.