* [ENHANCEMENT] UI: Add Collapse all button. #6957
* [ENHANCEMENT] UI: Clarify alert state toggle via checkbox icon. #7936
* [ENHANCEMENT] Add `rule_group_last_evaluation_samples` and `prometheus_tsdb_data_replay_duration_seconds` metrics. #7737#7977
* [ENHANCEMENT] Gracefully handle unknown WAL record types. #8004
* [ENHANCEMENT] Issue a warning for 64 bit systems running 32 bit binaries. #8012
* [BUGFIX] Adjust scrape timestamps to align them to the intended schedule, effectively reducing block size. Workaround for a regression in go1.14+. #7976
* [BUGFIX] promtool: Ensure alert rules are marked as restored in unit tests. #7661
* [BUGFIX] Eureka: Fix service discovery when compiled in 32-bit. #7964
* [BUGFIX] Don't do literal regex matching optimisation when case insensitive. #8013
* [BUGFIX] Fix classic UI sometimes running queries for instant query when in range query mode. #7984
## 2.21.0 / 2020-09-11
This release is built with Go 1.15, which deprecates [X.509 CommonName](https://golang.org/doc/go1.15#commonname)