Let's say I have this PromQL query:
node_disk_bytes_read * on(instance) group_left(node_name) node_meta{}
What is the purpose of group_left(node_name)? Specifically node_name. From what I understood, this lists all instance label values for the node_disk_bytes_read metric and all the combinations for the matching node_meta metric (many-to-one). But, what is the purpose of node_name in the grouping?