By the way, when you have very few devices to aggregate values from (let's say only 2 haproxy nodes), there's a trick you can use to still aggregate their values over peers, assuming you are willing to maintain different configurations on each node.

The principle is that there will be one table per metric and per node, and each node will track values using its own table. This way each table is written to by only one node, and all nodes get all the table updates. They are then free to watch other nodes' values in their respective tables.

Using the arithmetic converters it's even possible to add or average values between all tables, but then this quickly becomes complicated, as for example you can't easily take into account the number of online nodes in your operations. This is why this is mostly workable with two nodes and not really much more. In this case of two nodes, you either use your own value or the average operation if you can ping the neighbor.