> On 5 May 2015, at 1:19 pm, Zhou Zheng Sheng / 周征晟 <zhengsh...@awcloud.com> > wrote: > > Thank you Andrew. > > on 2015/05/05 08:03, Andrew Beekhof wrote: >>> On 28 Apr 2015, at 11:15 pm, Bogdan Dobrelya <bdobre...@mirantis.com> wrote: >>> >>>> Hello, >>> Hello, Zhou >>> >>>> I using Fuel 6.0.1 and find that RabbitMQ recover time is long after >>>> power failure. I have a running HA environment, then I reset power of >>>> all the machines at the same time. I observe that after reboot it >>>> usually takes 10 minutes for RabittMQ cluster to appear running >>>> master-slave mode in pacemaker. If I power off all the 3 controllers and >>>> only start 2 of them, the downtime sometimes can be as long as 20 minutes. >>> Yes, this is a known issue [0]. Note, there were many bugfixes, like >>> [1],[2],[3], merged for MQ OCF script, so you may want to try to >>> backport them as well by the following guide [4] >>> >>> [0] https://bugs.launchpad.net/fuel/+bug/1432603 >>> [1] https://review.openstack.org/#/c/175460/ >>> [2] https://review.openstack.org/#/c/175457/ >>> [3] https://review.openstack.org/#/c/175371/ >>> [4] https://review.openstack.org/#/c/170476/ >> Is there a reason you’re using a custom OCF script instead of the >> upstream[a] one? >> Please have a chat with David (the maintainer, in CC) if there is something >> you believe is wrong with it. >> >> [a] >> https://github.com/ClusterLabs/resource-agents/blob/master/heartbeat/rabbitmq-cluster > > I'm using the OCF script from the Fuel project, specifically from the > "6.0" stable branch [alpha].
Ah, I’m still learning who is who... i thought you were part of that project :-) > > Comparing with upstream OCF code, the main difference is that Fuel > RabbitMQ OCF is a master-slave resource. Fuel RabbitMQ OCF does more > bookkeeping, for example, blocking client access when RabbitMQ cluster > is not ready. I beleive the upstream OCF should be OK to use as well > after I read the code, but it might not fit into the Fuel project. As > far as I test, the Fuel OCF script is good except sometimes the full > reassemble time is long, and as I find out, it is mostly because the > Fuel MySQL Galera OCF script keeps pacemaker from promoting RabbitMQ > resource, as I mentioned in the previous emails. > > Maybe Vladimir and Sergey can give us more insight on why Fuel needs a > master-slave RabbitMQ. That would be good to know. Browsing the agent, promote seems to be a no-op if rabbit is already running. > I see Vladimir and Sergey works on the original > Fuel blueprint "RabbitMQ cluster" [beta]. > > [alpha] > https://github.com/stackforge/fuel-library/blob/stable/6.0/deployment/puppet/nova/files/ocf/rabbitmq > [beta] > https://blueprints.launchpad.net/fuel/+spec/rabbitmq-cluster-controlled-by-pacemaker > >>>> I have a little investigation and find out there are some possible causes. >>>> >>>> 1. MySQL Recovery Takes Too Long [1] and Blocking RabbitMQ Clustering in >>>> Pacemaker >>>> >>>> The pacemaker resource p_mysql start timeout is set to 475s. Sometimes >>>> MySQL-wss fails to start after power failure, and pacemaker would wait >>>> 475s before retry starting it. The problem is that pacemaker divides >>>> resource state transitions into batches. Since RabbitMQ is master-slave >>>> resource, I assume that starting all the slaves and promoting master are >>>> put into two different batches. If unfortunately starting all RabbitMQ >>>> slaves are put in the same batch as MySQL starting, even if RabbitMQ >>>> slaves and all other resources are ready, pacemaker will not continue >>>> but just wait for MySQL timeout. >>> Could you please elaborate the what is the same/different batches for MQ >>> and DB? Note, there is a MQ clustering logic flow charts available here >>> [5] and we're planning to release a dedicated technical bulletin for this. >>> >>> [5] http://goo.gl/PPNrw7 >>> >>>> I can re-produce this by hard powering off all the controllers and start >>>> them again. It's more likely to trigger MySQL failure in this way. Then >>>> I observe that if there is one cloned mysql instance not starting, the >>>> whole pacemaker cluster gets stuck and does not emit any log. On the >>>> host of the failed instance, I can see a mysql resource agent process >>>> calling the sleep command. If I kill that process, the pacemaker comes >>>> back alive and RabbitMQ master gets promoted. In fact this long timeout >>>> is blocking every resource from state transition in pacemaker. >>>> >>>> This maybe a known problem of pacemaker and there are some discussions >>>> in Linux-HA mailing list [2]. It might not be fixed in the near future. >>>> It seems in generally it's bad to have long timeout in state transition >>>> actions (start/stop/promote/demote). There maybe another way to >>>> implement MySQL-wss resource agent to use a short start timeout and >>>> monitor the wss cluster state using monitor action. >>> This is very interesting, thank you! I believe all commands for MySQL RA >>> OCF script should be as well wrapped with timeout -SIGTERM or -SIGKILL >>> as we did for MQ RA OCF. And there should no be any sleep calls. I >>> created a bug for this [6]. >>> >>> [6] https://bugs.launchpad.net/fuel/+bug/1449542 >>> >>>> I also find a fix to improve MySQL start timeout [3]. It shortens the >>>> timeout to 300s. At the time I sending this email, I can not find it in >>>> stable/6.0 branch. Maybe the maintainer needs to cherry-pick it to >>>> stable/6.0 ? >>>> >>>> [1] https://bugs.launchpad.net/fuel/+bug/1441885 >>>> [2] http://lists.linux-ha.org/pipermail/linux-ha/2014-March/047989.html >>>> [3] https://review.openstack.org/#/c/171333/ >>>> >>>> >>>> 2. RabbitMQ Resource Agent Breaks Existing Cluster >>>> >>>> Read the code of the RabbitMQ resource agent, I find it does the >>>> following to start RabbitMQ master-slave cluster. >>>> On all the controllers: >>>> (1) Start Erlang beam process >>>> (2) Start RabbitMQ App (If failed, reset mnesia DB and cluster state) >>>> (3) Stop RabbitMQ App but do not stop the beam process >>>> >>>> Then in pacemaker, all the RabbitMQ instances are in slave state. After >>>> pacemaker determines the master, it does the following. >>>> On the to-be-master host: >>>> (4) Start RabbitMQ App (If failed, reset mnesia DB and cluster state) >>>> On the slaves hosts: >>>> (5) Start RabbitMQ App (If failed, reset mnesia DB and cluster state) >>>> (6) Join RabbitMQ cluster of the master host >>>> >>> Yes, something like that. As I mentioned, there were several bug fixes >>> in the 6.1 dev, and you can also check the MQ clustering flow charts. >>> >>>> As far as I can understand, this process is to make sure the master >>>> determined by pacemaker is the same as the master determined in RabbitMQ >>>> cluster. If there is no existing cluster, it's fine. If it is run >>> after >>> >>> Not exactly. There is no master in mirrored MQ cluster. We define the >>> rabbit_hosts configuration option from Oslo.messaging. What ensures all >>> queue masters will be spread around all of MQ nodes in a long run. And >>> we use a master abstraction only for the Pacemaker RA clustering layer. >>> Here, a "master" is the MQ node what joins the rest of the MQ nodes. >>> >>>> power failure and recovery, it introduces the a new problem. >>> We do erase the node master attribute in CIB for such cases. This should >>> not bring problems into the master election logic. >>> >>>> After power recovery, if some of the RabbitMQ instances reach step (2) >>>> roughly at the same time (within 30s which is hard coded in RabbitMQ) as >>>> the original RabbitMQ master instance, they form the original cluster >>>> again and then shutdown. The other instances would have to wait for 30s >>>> before it reports failure waiting for tables, and be reset to a >>>> standalone cluster. >>>> >>>> In RabbitMQ documentation [4], it is also mentioned that if we shutdown >>>> RabbitMQ master, a new master is elected from the rest of slaves. If we >>> (Note, the RabbitMQ documentation mentions *queue* masters and slaves, >>> which are not the case for the Pacemaker RA clustering abstraction layer.) >>> >>>> continue to shutdown nodes in step (3), we reach a point that the last >>>> node is the RabbitMQ master, and pacemaker is not aware of it. I can see >>>> there is code to bookkeeping a "rabbit-start-time" attribute in >>>> pacemaker to record the most long lived instance to help pacemaker >>>> determine the master, but it does not cover the case mentioned above. >>> We made an assumption what the node with the highest MQ uptime should >>> know the most about recent cluster state, so other nodes must join it. >>> RA OCF does not work with queue masters directly. >>> >>>> A >>>> recent patch [5] checks existing "rabbit-master" attribute but it >>>> neither cover the above case. >>>> >>>> So in step (4), pacemaker determines a different master which was a >>>> RabbitMQ slave last time. It would wait for its original RabbitMQ master >>>> for 30s and fail, then it gets reset to a standalone cluster. Here we >>>> get some different clusters, so in step (5) and (6), it is likely to >>>> report error in log saying timeout waiting for tables or fail to merge >>>> mnesia database schema, then the those instances get reset. You can >>>> easily re-produce the case by hard resetting power of all the controllers. >>>> >>>> As you can see, if you are unlucky, there would be several "30s timeout >>>> and reset" before you finally get a healthy RabbitMQ cluster. >>> The full MQ cluster reassemble logic is far from the perfect state, >>> indeed. This might erase all mnesia files, hence any custom entities, >>> like users or vhosts, would be removed as well. Note, we do not >>> configure durable queues for Openstack so there is nothing to care about >>> here - the full cluster downtime assumes there will be no AMQP messages >>> stored at all. >>> >>>> I find three possible solutions. >>>> A. Using rabbitmqctl force_boot option [6] >>>> It will skips waiting for 30s and resetting cluster, but just assume the >>>> current node is the master and continue to operate. This is feasible >>>> because the original RabbitMQ master would discards the local state and >>>> sync with the new master after it joins a new cluster [7]. So we can be >>>> sure that after step (4) and (6), the pacemaker determined master >>>> instance is started unconditionally, and it will be the same as RabbitMQ >>>> master, and all operations run without 30s timeout. I find this option >>>> is only available in newer RabbitMQ release, and updating RabbitMQ might >>>> introduce other compatibility problems. >>> Yes, this option is only supported for newest RabbitMQ versions. But we >>> definitely should look how this could help. >>> >>>> B. Turn RabbitMQ into cloned instance and use pause_minority instead of >>>> autoheal [8] >>> Indeed, there are cases when MQ's autoheal can do nothing with existing >>> partitions and remains partitioned for ever, for example: >>> >>> Masters: [ node-1 ] >>> Slaves: [ node-2 node-3 ] >>> root@node-1:~# rabbitmqctl cluster_status >>> Cluster status of node 'rabbit@node-1' ... >>> [{nodes,[{disc,['rabbit@node-1','rabbit@node-2']}]}, >>> {running_nodes,['rabbit@node-1']}, >>> {cluster_name,<<"rabbit@node-2">>}, >>> {partitions,[]}] >>> ...done. >>> root@node-2:~# rabbitmqctl cluster_status >>> Cluster status of node 'rabbit@node-2' ... >>> [{nodes,[{disc,['rabbit@node-2']}]}] >>> ...done. >>> root@node-3:~# rabbitmqctl cluster_status >>> Cluster status of node 'rabbit@node-3' ... >>> [{nodes,[{disc,['rabbit@node-1','rabbit@node-2','rabbit@node-3']}]}, >>> {running_nodes,['rabbit@node-3']}, >>> {cluster_name,<<"rabbit@node-2">>}, >>> {partitions,[]}] >>> >>> So we should test the pause-minority value as well. >>> But I strongly believe we should make MQ multi-state clone to support >>> many masters, related bp [7] >>> >>> [7] >>> https://blueprints.launchpad.net/fuel/+spec/rabbitmq-pacemaker-multimaster-clone >>> >>>> This works like MySQL-wss. It let RabbitMQ cluster itself deal with >>>> partition in a manner similar to pacemaker quorum mechanism. When there >>>> is network partition, instances in the minority partition pauses >>>> themselves automatically. Pacemaker does not have to track who is the >>>> RabbitMQ master, who lives longest, who to promote... It just starts all >>>> the clones, done. This leads to huge change in RabbitMQ resource agent, >>>> and the stability and other impact is to be tested. >>> Well, we should not mess the queue masters and multi-clone master for MQ >>> resource in the pacemaker. >>> As I said, pacemaker RA has nothing to do with queue masters. And we >>> introduced this "master" mostly in order to support the full cluster >>> reassemble case - there must be a node promoted and other nodes should join. >>> >>>> C. Creating a "force_load" file >>>> After reading RabbitMQ source code, I find that the actual thing it does >>>> in solution A is just creating an empty file named "force_load" in >>>> mnesia database dir, then mnesia thinks it is the last node shut down in >>>> the last time and boot itself as the master. This implementation keeps >>>> the same from v3.1.4 to the latest RabbitMQ master branch. I think we >>>> can make use of this little trick. The change is adding just one line in >>>> "try_to_start_rmq_app()" function. >>>> >>>> touch "${MNESIA_FILES}/force_load" && \ >>>> chown rabbitmq:rabbitmq "${MNESIA_FILES}/force_load" >>> This is a very good point, thank you. >>> >>>> [4] http://www.rabbitmq.com/ha.html >>>> [5] https://review.openstack.org/#/c/169291/ >>>> [6] https://www.rabbitmq.com/clustering.html >>>> [7] http://www.rabbitmq.com/partitions.html#recovering >>>> [8] http://www.rabbitmq.com/partitions.html#automatic-handling >>>> >>>> Maybe you have better ideas on this. Please share your thoughts. >>> Thank you for a thorough feedback! This was a really great job. >>> >>>> ---- >>>> Best wishes! >>>> Zhou Zheng Sheng / ??? Software Engineer >>>> Beijing AWcloud Software Co., Ltd. >>>> >>> >>> -- >>> Best regards, >>> Bogdan Dobrelya, >>> Skype #bogdando_at_yahoo.com >>> Irc #bogdando >>> >>> __________________________________________________________________________ >>> OpenStack Development Mailing List (not for usage questions) >>> Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe >>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> >> __________________________________________________________________________ >> OpenStack Development Mailing List (not for usage questions) >> Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev