UPDATE: tagged as easy because the new cluster should be able to do the monthly aggregation in AQS (people are already requesting this data and aggregating it themselves so it doesn't increase the load on Cassandra, just the CPU usage on AQS, for which there is plenty of overhead).
Pageview API: https://wikitech.wikimedia.org/wiki/Analytics/PageviewAPI
Over many years  quite a few people asked for monthly page view stats that can be queried via an API.
Since medium 2015 we have the awesome api which serves highly granular pageview data. But for trend analysis or merely monthly reports a higher aggregation level would be very useful. And in particular monthly totals.
Daily and monthly aggregates are already available, as huge downloads from https://dumps.wikimedia.org/other/pagecounts-ez/merged/