6.0.0 Cannot perform rolling upgrade from cluster running 5.x to 6.0.0 when older bridges are in the configuration
Clusters that have started running from older EMQX versions that contain the now deprecated bridges configuration root will fail to sync their configuration to the new 6.0 nodes, because the latter have dropped for such roots and thus fail to start the corresponding Connectors, Actions and Sources. Starting from 6.0.1, an RPC call is made to the older node to upgrade the configuration to convert bridges into connectors, sources and actions, facilitating rolling upgrades with less manual invervention.
Alternatively, each affected bridge can be updated via HTTP API or CLI to induce a configuration update (e.g., change the description) which will also upgrade the persisted cluster.hocon file.
The following Connector/Sources/Actions might still require manual changes before attempting a rolling upgrade:
– GCP PubSub Consumer
– Kafka Consumer
If there are any such sources in the configuration that still contain the topic_mapping field, the field must be removed from config and then one “Source + Rule” pair must be created for each entry.

6.0.0 Cannot perform rolling upgrade from cluster running 5.x to 6.0.0 when older bridges are in the configuration
Clusters that have started running from older EMQX versions that contain the now deprecated bridges configuration root will fail to sync their configuration to the new 6.0 nodes, because the latter have dropped for such roots and thus fail to start the corresponding Connectors, Actions and Sources. Starting from 6.0.1, an RPC call is made to the older node to upgrade the configuration to convert bridges into connectors, sources and actions, facilitating rolling upgrades with less manual invervention.
Alternatively, each affected bridge can be updated via HTTP API or CLI to induce a configuration update (e.g., change the description) which will also upgrade the persisted cluster.hocon file.
The following Connector/Sources/Actions might still require manual changes before attempting a rolling upgrade:
– GCP PubSub Consumer
– Kafka Consumer
If there are any such sources in the configuration that still contain the topic_mapping field, the field must be removed from config and then one “Source + Rule” pair must be created for each entry.