Handle premature connection termination in connection tracking handler

[gerhard]

Proposed Changes

If a connection disappears before the handler can get the relevant info from a connection_created event, the handler crashes.

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Further Comments

Not sure if this is a good idea, submitting it while in WIP to get some feedback. I'm looking at how to add a test for this - feels very complicated - is it worth it?

Discovered by @mkuratczyk

2019-02-21 16:47:03.086 [info] <0.1283.0> accepting AMQP connection <0.1283.0> (10.44.1.56:34784 -> 10.44.0.54:5672)
2019-02-21 16:47:03.239 [info] <0.1283.0> Connection <0.1283.0> (10.44.1.56:34784 -> 10.44.0.54:5672) has a client-provided name: perf-test-configuration
2019-02-21 16:47:03.254 [info] <0.1283.0> connection <0.1283.0> (10.44.1.56:34784 -> 10.44.0.54:5672 - perf-test-configuration): user 'test' authenticated and granted access to vhost '/'
2019-02-21 16:47:03.256 [error] <0.392.0> ** gen_event handler rabbit_connection_tracking_handler crashed.
** Was installed in rabbit_event
** Last event was: {event,connection_created,[{user_provided_name,<<"perf-test-configuration">>},{type,network},{pid,<0.1283.0>},{name,<<"10.44.1.56:34784 -> 10.44.0.54:5672">>},{port,5672},{peer_port,34784},{host,{0,0,0,0,0,65535,2604,54}},{peer_host,{0,0,0,0,0,65535,2604,312}},{ssl,false},{peer_cert_subject,''},{peer_cert_issuer,''},{peer_cert_validity,''},{auth_mechanism,<<"PLAIN">>},{ssl_protocol,''},{ssl_key_exchange,''},{ssl_cipher,''},{ssl_hash,''},{protocol,{0,9,1}},{user,<<"test">>},{vhost,<<"/">>},{timeout,60},{frame_max,131072},{channel_max,2047},{client_properties,[{<<"connection_name">>,longstr,<<"perf-test-configuration">>},{<<"product">>,longstr,<<"RabbitMQ">>},{<<"copyright">>,longstr,<<"Copyright (c) 2007-2019 Pivotal Software, Inc.">>},{<<"capabilities">>,table,[{<<"exchange_exchange_bindings">>,bool,true},{<<"connection.blocked">>,bool,true},{<<"authentication_failure_close">>,bool,true},{<<"basic.nack">>,bool,true},{<<"publisher_confirms">>,bool,true},{<<"consumer_cancel_notify">>,bool,true}]},{<<"information">>,longstr,<<"Licensed under the MPL. See http://www.rabbitmq.com/">>},{<<"version">>,longstr,<<"5.6.0">>},{<<"platform">>,longstr,<<"Java">>}]},{connected_at,1550767623053},{node,'[email protected]'},...],...}
** When handler state == []
** Reason == {error,{no_exists,['tracked_connection_on_node_rabbit@rabbitmq-2.rabbitmq-headless.rabbitmq.svc.cluster.local',{'[email protected]',<<"10.44.1.56:34784 -> 10.44.0.54:5672">>}]}}
2019-02-21 16:47:03.302 [info] <0.1292.0> accepting AMQP connection <0.1292.0> (10.44.1.56:34788 -> 10.44.0.54:5672)
2019-02-21 16:47:03.333 [info] <0.1292.0> Connection <0.1292.0> (10.44.1.56:34788 -> 10.44.0.54:5672) has a client-provided name: perf-test-consumer-0
2019-02-21 16:47:03.336 [info] <0.1292.0> connection <0.1292.0> (10.44.1.56:34788 -> 10.44.0.54:5672 - perf-test-consumer-0): user 'test' authenticated and granted access to vhost '/'
2019-02-21 16:47:03.942 [info] <0.1315.0> accepting AMQP connection <0.1315.0> (10.44.0.56:49878 -> 10.44.0.54:5672)
2019-02-21 16:47:03.963 [info] <0.1315.0> Connection <0.1315.0> (10.44.0.56:49878 -> 10.44.0.54:5672) has a client-provided name: perf-test-consumer-0
2019-02-21 16:47:03.972 [info] <0.1315.0> connection <0.1315.0> (10.44.0.56:49878 -> 10.44.0.54:5672 - perf-test-consumer-0): user 'test' authenticated and granted access to vhost '/'
2019-02-21 16:47:04.038 [info] <0.1337.0> accepting AMQP connection <0.1337.0> (10.44.0.56:49880 -> 10.44.0.54:5672)
2019-02-21 16:47:04.044 [info] <0.1337.0> Connection <0.1337.0> (10.44.0.56:49880 -> 10.44.0.54:5672) has a client-provided name: perf-test-producer-0
2019-02-21 16:47:04.048 [info] <0.1337.0> connection <0.1337.0> (10.44.0.56:49880 -> 10.44.0.54:5672 - perf-test-producer-0): user 'test' authenticated and granted access to vhost '/'

[lukebakken]

I think rabbit_connection_tracking:register_connection should be updated, instead, as there are other mnesia operations in that module that handle no_exists

[gerhard]

Happy for @lukebakken to take this over 👍

[lukebakken]

@michaelklishin if we're going to catch these errors, how about moving try ... catch into rabbit_connection_tracking:register_connection itself?

[michaelklishin]

But it's the handler's choice/responsibility to handle them. I don't know if we want to mask those errors for every caller and what the return value should be in that case.

[lukebakken]

OK

[lukebakken]

Backported to v3.7.x