fix querier panics when query exemplars (#4473)

* fix querier panics when query exemplars

Signed-off-by: nous23 <cchen23@outlook.com>

* Update CHANGELOG.md

Co-authored-by: Peter Štibraný <pstibrany@gmail.com>
Signed-off-by: nous23 <cchen23@outlook.com>

Co-authored-by: Peter Štibraný <pstibrany@gmail.com>

Author: nous23

CHANGELOG.md

@@ -50,6 +50,7 @@
 * [BUGFIX] Querier: After query-frontend restart, querier may have lower than configured concurrency. #4417
 * [BUGFIX] Memberlist: forward only changes, not entire original message. #4419
 * [BUGFIX] Memberlist: don't accept old tombstones as incoming change, and don't forward such messages to other gossip members. #4420
+* [BUGFIX] Querier: fixed panic when querying exemplars and using `-distributor.shard-by-all-labels=false`. #4473
 
 ## 1.10.0 / 2021-08-03
 

pkg/distributor/query.go

@@ -59,7 +59,7 @@ func (d *Distributor) QueryExemplars(ctx context.Context, from, to model.Time, m
 		}
 
 		// We ask for all ingesters without passing matchers because exemplar queries take in an array of array of label matchers.
-		replicationSet, err := d.GetIngestersForQuery(ctx, nil)
+		replicationSet, err := d.GetIngestersForQuery(ctx)
 		if err != nil {
 			return err
 		}