Highlights:

• Added new Thanos component: Query Frontend responsible for response caching,
  query scheduling and parallelization (based on Cortex Query Frontend).
• Added various new, improved UIs to Thanos based on React: Querier' BuildInfo & Flags, Ruler UI, BlockViewer.
• Optimized Sidecar, Store, Receive, Ruler data retrieval with new TSDB ChunkIterator, capping chunks to 120 samples, fixed various leaks.
• Fixed sample limit on Store Gateway.
• Added S3 Server Side Encryption options.
• Tons of other important fixes!

Thanks to all contributors! 🤗

Fixed

• #2665 Swift: Fix issue with missing Content-Type HTTP headers.
• #2800 Query: Fix handling of --web.external-prefix and --web.route-prefix.
• #2834 Query: Fix rendered JSON state value for rules and alerts should be in lowercase.
• #2866 Receive, Querier: Fixed leaks on receive and querier Store API Series, which were leaking on errors.
• #2937 Receive: Fixing auto-configuration of --receive.local-endpoint.
• #2895 Compact: Fix increment of thanos_compact_downsample_total metric for downsample of 5m resolution blocks.
• #2858 Store: Fix --store.grpc.series-sample-limit implementation. The limit is now applied to the sum of all samples fetched across all queried blocks via a single Series call, instead of applying it individually to each block.
• #2936 Compact: Fix ReplicaLabelRemover panic when replicaLabels are not specified.
• #2956 Store: Fix fetching of chunks bigger than 16000 bytes.
• #2970 Store: Upgrade minio-go/v7 to fix slowness when running on EKS.
• #2957 Rule: breaking ⚠️ Now sets all of the relevant fields properly; avoids a panic when /api/v1/rules is called and the time zone is not UTC; rules field is an empty array now if no rules have been defined in a rule group.
  Thanos Rule's /api/v1/rules endpoint no longer returns the old, deprecated partial_response_strategy. The old, deprecated value has been fixed to WARN for quite some time. Please use partialResponseStrategy.
• #2976 Query: Better rounding for incoming query timestamps.
• #2929 Mixin: Fix expression for 'unhealthy sidecar' alert and increase the timeout for 10 minutes.
• #3024 Query: Consider group name and file for deduplication.
• #3012 Ruler,Receiver: Fix TSDB to delete blocks in atomic way.
• #3046 Ruler,Receiver: Fixed framing of StoreAPI response, it was one chunk by one.
• #3095 Ruler: Update the manager when all rule files are removed.
• #3105 Querier: Fix overwriting maxSourceResolution when auto downsampling is enabled.
• #3010 Querier: Added --query.lookback-delta flag to override the default lookback delta in PromQL. The flag should be lookback delta should be set to at least 2 times of the slowest scrape interval. If unset it will use the PromQL default of 5m.

Added

• #2305 Receive,Sidecar,Ruler: Propagate correct (stricter) MinTime for TSDBs that have no block.
• #2849 Query, Ruler: Added request logging for HTTP server side.
• #2832 ui React: Add runtime and build info page
• #2926 API: Add new blocks HTTP API to serve blocks metadata. The status endpoints (/api/v1/status/flags, /api/v1/status/runtimeinfo and /api/v1/status/buildinfo) are now available on all components with a HTTP API.
• #2892 Receive: Receiver fails when the initial upload fails.
• #2865 ui: Migrate Thanos Ruler UI to React
• #2964 Query: Add time range parameters to label APIs. Add start and end fields to Store API LabelNamesRequest and LabelValuesRequest.
• #2996 Sidecar: Add reloader_config_apply_errors_total metric. Add new flags --reloader.watch-interval, and --reloader.retry-interval.
• #2973 Add Thanos Query Frontend component.
• #2980 Bucket Viewer: Migrate block viewer to React.
• #2725 Add bucket index operation durations: thanos_bucket_store_cached_series_fetch_duration_seconds and thanos_bucket_store_cached_postings_fetch_duration_seconds.
• #2931 Query: Allow passing a storeMatch[] to select matching stores when debugging the querier. See documentation

Changed

• #2893 Store: Rename metric thanos_bucket_store_cached_postings_compression_time_seconds to thanos_bucket_store_cached_postings_compression_time_seconds_total.
• #2915 Receive,Ruler: Enable TSDB directory locking by default. Add a new flag (--tsdb.no-lockfile) to override behavior.
• #2902 Querier UI:Separate dedupe and partial response checkboxes per panel in new UI.
• #2991 Store: breaking ⚠️ operation label value getrange changed to get_range for thanos_store_bucket_cache_operation_requests_total and thanos_store_bucket_cache_operation_hits_total to be consistent with bucket operation metrics.
• #2876 Receive,Ruler: Updated TSDB and switched to ChunkIterators instead of sample one, which avoids unnecessary decoding / encoding.
• #3064 s3: breaking ⚠️ Add SSE/SSE-KMS/SSE-C configuration. The S3 encrypt_sse: true option is now deprecated in favour of sse_config. If you used encrypt_sse, the migration strategy is to set up the following block:

sse_config:
  type: SSE-S3