Thanks for the detailed report and the reproduction. They made this easy to track down.
- Is this a known issue?
It was not a known issue, so we have reported it to OpenSearch: [BUG] filter aggregation with `now` date math intermittently fails with "DateRangeIncludingNowQuery ... does not implement createWeight" under concurrent segment search · Issue #23104 · opensearch-project/OpenSearch · GitHub
Our investigation shows that it is an OpenSearch bug introduced in 3.2.0. It is not caused by Fess or by the date math: now/d-1d, now-1d/d and now-1d all fail the same way. We could reproduce it on plain OpenSearch 3.2.0 and 3.8.0, but not on 3.1.0. It only happens when a single-bucket filter aggregation uses a now-based range and concurrent segment search is active. Fess builds its date facets exactly that way.
- Workaround
Disable concurrent segment search on the Fess index. fess.search is an alias, so first look up the actual index name:
GET _cat/aliases/fess.search?v
Then apply the setting to that index, for example fess.20260917:
PUT fess.20260917/_settings
{ "index.search.concurrent_segment_search.mode": "none" }
This is a dynamic setting, so it takes effect immediately; you do not need to close the index or restart OpenSearch. In our tests the failures stopped completely with none. The only effect is that aggregations no longer run in parallel within a shard. If the Fess index is ever recreated, for example by a reindex, apply the setting again to the new index.
- Timeout vs. shard failure message
You are right. Fess 15.8 treats any failed shard as a “timeout”. This is fixed in the upcoming Fess 15.9 (fix(search): tell a query timeout apart from a failed shard by marevol · Pull Request #3440 · codelibs/fess · GitHub): a timeout and a shard failure are now reported separately. Until then, if you see this message on 15.8, the cause is more likely a shard failure than a timeout. The real reason is in the _shards.failures part of the [SEARCH TIMEOUT] log line.
- Where to report
No Fess issue is needed. The OpenSearch issue above covers it.