When moving between patch (also known as incremental) version changes such as 0.1.0 to 0.1.1 users should be safe to assume a clean upgrade can occur with no risk of behavior changes other than bug fixes and no compatibility issues.
When moving between minor changes such as 0.1.0 to 0.2.0 users can expect new behaviors and bug fixes but backward compatibility should be protected.
When moving between major changes such as 0.x.y to 1.0.0 t here may be backward compatibility impacting changes largely focused on removal of deprecated items.

Migrating to 1.19.0

For users of the apace/nifi* Docker images, note that the base image changed to eclipse-temurin:jre-11 from openjdk:8-jre. This could cause build issues if you were using the Apache NiFi docker image(s) as a base for custom images, or otherwise have functionality that requires packages from the base image and not NiFi itself. It is recommended to test in a dev environment prior to migrating to 1.19.0/latest image tags.

Migrating to 1.17.0

This release deprecated support for RocksDBFlowFileRepository. The RocksDB repository is packaged in a separate NAR named nifi-rocksdb-nar, available for download from Maven Central
This release removed Hive 1.2 components from the standard release binary. The nifi-hive-nar and nifi-hive-services-api-nar modules can be downloaded from Maven Central
This release upgraded Apache Avro to version 1.11.0 (NIFI-7234). This version of Avro changes the behavior where you could previously have aliases for fields with a null value (AVRO-2278), and thereby introduces a bug in NiFi that will be resolved in NiFi 1.19.0 (NIFI-10660).

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