Mark Payne created NIFI-6849:
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Summary: On startup, NiFi should be more liberal about what it's
willing to inherit from cluster
Key: NIFI-6849
URL: https://issues.apache.org/jira/browse/NIFI-6849
Project: Apache NiFi
Issue Type: Improvement
Components: Core Framework
Reporter: Mark Payne
Assignee: Mark Payne
On startup, if an instance is configured to be clustered, the instance must
connect to the Cluster Coordinator and download the existing cluster flow,
access policies, and users and groups. The instance then performs some checks
to ensure that the local flow matches the cluster's flow. If it doesn't, then
the node fails to startup and logs errors that the local flow is different than
the cluster's flow.
This was done in order to facilitate debugging. If a particular node is not
behaving as expected, a user is able to disconnect the node from the cluster
and make modifications to the node. If the node is then restarted, it may not
be desirable to lose those changes.
However, in the vast majority of cases (probably over 98% of the time), what
the user really wants is for the node to just join back to the cluster and
inherit the cluster's flow - especially if the node just disconnected because
it failed to make a modification. This is also problematic with how the Users,
Groups, and Policies are inherited.
As a result, we should make the following modifications:
1) If Users, Groups, or Access Policies cannot be inherited, continue to fail,
unless the flow is empty. If the flow is empty, it doesn't really make sense to
retain the authorizations' configuration because they don't really apply to
anything. As a result, if the flow is empty, just inherit whatever the cluster
has. But first, make a backup of the existing policies, users, and groups, so
that users can manually revert if they do end up needing to.
2) If the flow differs from the cluster flow, check the proposed flow to see if
it removes any existing connections. If it does remove a connection, and that
connection has data queued locally, continue to fail. Otherwise, create a
backup of the flow and replace the node's flow with the cluster flow.
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