Many plugins can now be run in a mode that avoids implicit conflict with the Elastic Common Schema (ECS). This mode is controlled individually with each plugin’s ecs_compatibility option, which defaults to the value of the Logstash pipeline.ecs_compatibility setting. In Logstash 8, this compatibility mode will be on-by-default for all pipelines.
If you wish to lock in a pipeline’s behavior from Logstash 7.x before upgrading to Logstash 8, you can set pipeline.ecs_compatibility: disabled to its definition in pipelines.yml (or globally in logstash.yml).