Previously, config_updater used a serialized_action to trigger update_config() when object_storage_endpoints changed. Because serialized_action::trigger() always schedules the action as a new reactor task (via semaphore::wait().then()), there was a window between the config value becoming visible to the REST API and update_config() actually running. This allowed a concurrent CREATE KEYSPACE to see the new endpoint via is_known_endpoint() before storage_manager had registered it in _object_storage_endpoints.
Now config observers run synchronously in a reactor turn and must not suspend. Split the previous monolithic async update_config() coroutine into two phases:
- Sync (in the observer, never suspends): storage_manager::_object_storage_endpoints is updated in place; for already-instantiated clients, update_config_sync swaps the new config atomically
- Async (per-client gate): background fibers finish the work that can't run in the observer — S3 refreshes credentials under _creds_sem; GCS drains and closes the replaced client.
Config reloads triggered by SIGHUP are applied on shard 0 and then broadcast to all other shards. An rwlock has been also introduced to make sure that the configuration has been propagated to all cores. This guarantees that a client requesting a config via the REST API will see a consistent snapshot
Fixes: https://scylladb.atlassian.net/browse/SCYLLADB-757
Fixes: [28141](https://github.com/scylladb/scylladb/issues/28141)
Closesscylladb/scylladb#28950
* github.com:scylladb/scylladb:
test/object_store: verify object storage client creation and live reconfiguration
sstables/utils/s3: split config update into sync and async parts
test_config: improve logging for wait_for_config API
db: introduce read-write lock to synchronize config updates with REST API
33682fd14e