Clarify documentation on series endpoint (#2953)

* clarify limitation for /series endpoint

Signed-off-by: Jakob Kartschall <[email protected]>

* update changelog

Signed-off-by: Jakob Kartschall <[email protected]>

* add note about queries to ingesters without __name__ label

Signed-off-by: Jakob Kartschall <[email protected]>

Author: Jakob Kartschall

CHANGELOG.md

@@ -87,6 +87,7 @@
 * [ENHANCEMENT] Flusher: Added `-flusher.exit-after-flush` option (defaults to true) to control whether Cortex should stop completely after Flusher has finished its work. #2877
 * [ENHANCEMENT] Added metrics `cortex_config_hash` and `cortex_runtime_config_hash` to expose hash of the currently active config file. #2874
 * [ENHANCEMENT] Logger: added JSON logging support, configured via the `-log.format=json` CLI flag or its respective YAML config option. #2386
+* [ENHANCEMENT] Clarify limitations of the `/api/v1/series`, `/api/v1/labels` and `/api/v1/label/{name}/values` endpoints. #2953
 * [BUGFIX] Fixed a bug in the index intersect code causing storage to return more chunks/series than required. #2796
 * [BUGFIX] Fixed the number of reported keys in the background cache queue. #2764
 * [BUGFIX] Fix race in processing of headers in sharded queries. #2762

docs/configuration/v1-guarantees.md

@@ -23,7 +23,8 @@ The Cortex maintainers commit to ensuring future version of Cortex can read data
 
 Cortex strives to be 100% API compatible with Prometheus (under `/api/prom/*`); any deviation from this is considered a bug, except:
 
-- Requiring the `__name__` label on queries.
+- Requiring the `__name__` label on queries when querying the chunks storage (queries to ingesters or clusters running the blocks storage are not affected).
+- For queries to the `/api/v1/series`, `/api/v1/labels` and `/api/v1/label/{name}/values` endpoints, query's time range is ignored and the data is always fetched from ingesters.
 - Additional API endpoints for creating, removing and modifying alerts and recording rules.
 - Additional API around pushing metrics (under `/api/push`).
 - Additional API endpoints for management of Cortex itself, such as the ring.  These APIs are not part of the any compatibility guarantees.