rabbit_feature_flags: Take callback definition from correct node #12966
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[Why]
The feature flag controller that is responsible for enabling a feature
flag may be on a node that doesn't know this feature flag. This is
supported by there is a bug when it queries the callback definition for
that feature flag: it uses its own registry which does not have anything
about this feature flag.
This leads to a crash because the `run_callback/5` funtion tries to use
the `undefined` atom returned by the registry as a map:
crasher:
initial call: rabbit_ff_controller:init/1
pid: <0.374.0>
registered_name: rabbit_ff_controller
exception error: bad map: undefined
in function rabbit_ff_controller:run_callback/5
in call from rabbit_ff_controller:do_enable/3 (rabbit_ff_controller.erl, line 1244)
in call from rabbit_ff_controller:update_feature_state_and_enable/2 (rabbit_ff_controller.erl, line 1180)
in call from rabbit_ff_controller:enable_with_registry_locked/2 (rabbit_ff_controller.erl, line 1050)
in call from rabbit_ff_controller:enable_many_locked/2 (rabbit_ff_controller.erl, line 991)
in call from rabbit_ff_controller:enable_many/2 (rabbit_ff_controller.erl, line 979)
in call from rabbit_ff_controller:updating_feature_flag_states/3 (rabbit_ff_controller.erl, line 307)
in call from gen_statem:loop_state_callback/11 (gen_statem.erl, line 3735)
[How]
The callback definition is now queried from the first node in the list
given as argument. For the common use case where all nodes know about a
feature flag, the first node is the local one, so there should be no
latency caused by the RPC.
See #12963.
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Why
The feature flag controller that is responsible for enabling a feature flag may be on a node that doesn't know this feature flag. This is supported by there is a bug when it queries the callback definition for that feature flag: it uses its own registry which does not have anything about this feature flag.
This leads to a crash because the
run_callback/5funtion tries to use theundefinedatom returned by the registry as a map:How
The callback definition is now queried from the first node in the list given as argument. For the common use case where all nodes know about a feature flag, the first node is the local one, so there should be no latency caused by the RPC.
See #12963.