Make it clear ingestion rate global limit requires evenly balanced traffic to distributors (#1943)

Signed-off-by: Marco Pracucci <[email protected]>

Author: pracucci

docs/configuration/arguments.md

@@ -306,7 +306,7 @@ Valid fields are (with their corresponding flags for default values):
 
   The `local` strategy enforces the limit on a per distributor basis, actual effective rate limit will be N times higher, where N is the number of distributor replicas.
 
-  The `global` strategy enforces the limit globally, configuring a per-distributor local rate limiter as `ingestion_rate / N`, where N is the number of distributor replicas (it's automatically adjusted if the number of replicas change). The `ingestion_burst_size` refers to the per-distributor local rate limiter (even in the case of the `global` strategy) and should be set at least to the maximum number of samples expected in a single push request.
+  The `global` strategy enforces the limit globally, configuring a per-distributor local rate limiter as `ingestion_rate / N`, where N is the number of distributor replicas (it's automatically adjusted if the number of replicas change). The `ingestion_burst_size` refers to the per-distributor local rate limiter (even in the case of the `global` strategy) and should be set at least to the maximum number of samples expected in a single push request. For this reason, the `global` strategy requires that push requests are evenly distributed across the pool of distributors; if you use a load balancer in front of the distributors you should be already covered, while if you have a custom setup (ie. an authentication gateway in front) make sure traffic is evenly balanced across distributors.
 
   The `global` strategy requires the distributors to form their own ring, which is used to keep track of the current number of healthy distributor replicas. The ring is configured by `distributor: { ring: {}}` / `-distributor.ring.*`.