## Tracer
### Added
- Add a new decision maker mechanism #1598
- Rename DD_TRACE_X_DATADOG_TAGS_PROPAGATE_SERVICE to DD_TRACE_PROPAGATE_SERVICE #1612, #1613
- Add support for unix domain sockets #1601
- Add RedisCluster split by host #1602 (Thanks to @radykal-com)
- Add http.useragent to root span #1607
### Fixed
- Fix #1582: *_id keys in meta and metrics are wrongly encoded #1599
- Fix dlerror logging format #1605
- Fix DD_TRACE_URL_AS_RESOURCE_NAMES_ENABLED accidentally guarding http.method and http.url as well #1608
### Internal changes
- Fix downstream job trigger for deployments to rel-env #1597
- Update dd-trace-php link for reliability environment #1595
- Move request-replayer from our internal deprecated repository to dd-trace-php #1600
- Support restricting PHP versions while running randomized tests #1604
- Transition to non-legacy circleci images #1609