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From Marc-Aurèle Brothier <ma...@exoscale.ch>
Subject Re: [Discuss] Management cluster / Zookeeper holding locks
Date Mon, 18 Dec 2017 10:32:02 GMT
@rafael, yes there is a framework (curator), it's the link I posted in my
first message: https://curator.apache.org/curator-recipes/shared-lock.html
This framework helps handling all the complexity of ZK.

The ZK client stays connected all the time (as the DB connection pool), and
only one connection (ZKClient) is needed to communicate with the ZK server.
The framework handles reconnection as well.

Have a look at ehc curator website to understand its goal:
https://curator.apache.org/

On Mon, Dec 18, 2017 at 11:01 AM, Rafael Weingärtner <
rafaelweingartner@gmail.com> wrote:

> Do we have framework to do this kind of looking in ZK?
> I mean, you said " create a new InterProcessSemaphoreMutex which handles
> the locking mechanism.". This feels that we would have to continue opening
> and closing this transaction manually, which is what causes a lot of our
> headaches with transactions (it is not MySQL locks fault entirely, but our
> code structure).
>
> On Mon, Dec 18, 2017 at 7:47 AM, Marc-Aurèle Brothier <marco@exoscale.ch>
> wrote:
>
> > We added ZK lock for fix this issue but we will remove all current locks
> in
> > ZK in favor of ZK one. The ZK lock is already encapsulated in a project
> > with an interface, but more work should be done to have a proper
> interface
> > for locks which could be implemented with the "tool" you want, either a
> DB
> > lock for simplicity, or ZK for more advanced scenarios.
> >
> > @Daan you will need to add the ZK libraries in CS and have a running ZK
> > server somewhere. The configuration value is read from the
> > server.properties. If the line is empty, the ZK client is not created and
> > any lock request will immediately return (not holding any lock).
> >
> > @Rafael: ZK is pretty easy to setup and have running, as long as you
> don't
> > put too much data in it. Regarding our scenario here, with only locks,
> it's
> > easy. ZK would be only the gatekeeper to locks in the code, ensuring that
> > multi JVM can request a true lock.
> > For the code point of view, you're opening a connection to a ZK node (any
> > of a cluster) and you create a new InterProcessSemaphoreMutex which
> handles
> > the locking mechanism.
> >
> > On Mon, Dec 18, 2017 at 10:24 AM, Ivan Kudryavtsev <
> > kudryavtsev_ia@bw-sw.com
> > > wrote:
> >
> > > Rafael,
> > >
> > > - It's easy to configure and run ZK either in single node or cluster
> > > - zookeeper should replace mysql locking mechanism used inside ACS code
> > > (places where ACS locks tables or rows).
> > >
> > > I don't think from the other size, that moving from MySQL locks to ZK
> > locks
> > > is easy and light and (even implemetable) way.
> > >
> > > 2017-12-18 16:20 GMT+07:00 Rafael Weingärtner <
> > rafaelweingartner@gmail.com
> > > >:
> > >
> > > > How hard is it to configure Zookeeper and get everything up and
> > running?
> > > > BTW: what zookeeper would be managing? CloudStack management servers
> or
> > > > MySQL nodes?
> > > >
> > > > On Mon, Dec 18, 2017 at 7:13 AM, Ivan Kudryavtsev <
> > > > kudryavtsev_ia@bw-sw.com>
> > > > wrote:
> > > >
> > > > > Hello, Marc-Aurele, I strongly believe that all mysql locks should
> be
> > > > > removed in favour of truly DLM solution like Zookeeper. The
> > performance
> > > > of
> > > > > 3node ZK ensemble should be enough to hold up to 1000-2000 locks
> per
> > > > second
> > > > > and it helps to move to truly clustered MySQL like galera without
> > > single
> > > > > master server.
> > > > >
> > > > > 2017-12-18 15:33 GMT+07:00 Marc-Aurèle Brothier <marco@exoscale.ch
> >:
> > > > >
> > > > > > Hi everyone,
> > > > > >
> > > > > > I was wondering how many of you are running CloudStack with
a
> > cluster
> > > > of
> > > > > > management servers. I would think most of you, but it would
be
> nice
> > > to
> > > > > hear
> > > > > > everyone voices. And do you get hosts going over their capacity
> > > limits?
> > > > > >
> > > > > > We discovered that during the VM allocation, if you get a lot
of
> > > > parallel
> > > > > > requests to create new VMs, most notably with large profiles,
the
> > > > > capacity
> > > > > > increase is done too far after the host capacity checks and
> results
> > > in
> > > > > > hosts going over their capacity limits. To detail the steps:
the
> > > > > deployment
> > > > > > planner checks for cluster/host capacity and pick up one
> deployment
> > > > plan
> > > > > > (zone, cluster, host). The plan is stored in the database under
a
> > > > VMwork
> > > > > > job and another thread picks that entry and starts the
> deployment,
> > > > > > increasing the host capacity and sending the commands. Here
> > there's a
> > > > > time
> > > > > > gap between the host being picked up and the capacity increase
> for
> > > that
> > > > > > host of a couple of seconds, which is well enough to go over
the
> > > > capacity
> > > > > > on one or more hosts. A few VMwork job can be added in the DB
> queue
> > > > > > targeting the same host before one gets picked up.
> > > > > >
> > > > > > To fix this issue, we're using Zookeeper to act as the multi
JVM
> > lock
> > > > > > manager thanks to their curator library (
> > > > > > https://curator.apache.org/curator-recipes/shared-lock.html).
We
> > > also
> > > > > > changed the time when the capacity is increased, which occurs
now
> > > > pretty
> > > > > > much after the deployment plan is found and inside the zookeeper
> > > lock.
> > > > > This
> > > > > > ensure we don't go over the capacity of any host, and it has
been
> > > > proven
> > > > > > efficient since a month in our management server cluster.
> > > > > >
> > > > > > This adds another potential requirement which should be discuss
> > > before
> > > > > > proposing a PR. Today the code works seamlessly without ZK too,
> to
> > > > ensure
> > > > > > it's not a hard requirement, for example in a lab.
> > > > > >
> > > > > > Comments?
> > > > > >
> > > > > > Kind regards,
> > > > > > Marc-Aurèle
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > With best regards, Ivan Kudryavtsev
> > > > > Bitworks Software, Ltd.
> > > > > Cell: +7-923-414-1515
> > > > > WWW: http://bitworks.software/ <http://bw-sw.com/>
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Rafael Weingärtner
> > > >
> > >
> > >
> > >
> > > --
> > > With best regards, Ivan Kudryavtsev
> > > Bitworks Software, Ltd.
> > > Cell: +7-923-414-1515
> > > WWW: http://bitworks.software/ <http://bw-sw.com/>
> > >
> >
>
>
>
> --
> Rafael Weingärtner
>

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