airavata-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Supun Kamburugamuva <supu...@gmail.com>
Subject Re: Zookeeper in Airavata to achieve reliability
Date Fri, 13 Jun 2014 03:50:01 GMT
Hi all,

Here is what I think about Airavata and ZooKeeper. In Airavata there are
many components and these components must be stateless to achieve
scalability and reliability.Also there must be a mechanism to communicate
between the components. At the moment Airavata uses RPC calls based on
Thrift for the communication.

ZooKeeper can be used both as a place to hold state and as a communication
layer between the components. I'm involved with a project that has many
distributed components like AIravata. Right now we use Thrift services to
communicate among the components. But we find it difficult to use RPC calls
and achieve stateless behaviour and thinking of replacing Thrift services
with ZooKeeper based communication layer. So I think it is better to
explore the possibility of removing the Thrift services between the
components and use ZooKeeper as a communication mechanism between the
services. If you do this you will have to move the state to ZooKeeper and
will automatically achieve the stateless behaviour in the components.

Also I think trying to make ZooKeeper optional is a bad idea. If we are
trying to integrate something fundamentally important to architecture as
how to store state, we shouldn't make it optional.

Thanks,
Supun..


On Thu, Jun 12, 2014 at 10:57 PM, Shameera Rathnayaka <
shameerainfo@gmail.com> wrote:

> Hi Lahiru,
>
> As i understood,  not only reliability , you are trying to achieve some
> other requirement by introducing zookeeper, like health monitoring of the
> services, categorization with service implementation etc ... . In that
> case, i think we can get use of zookeeper's features but if we only focus
> on reliability, i have little bit of concern, why can't we use clustering +
> LB ?
>
> Yes it is better we add Zookeeper as a prerequisite if user need to use
> it.
>
> Thanks,
>  Shameera.
>
>
> On Thu, Jun 12, 2014 at 5:19 AM, Lahiru Gunathilake <glahiru@gmail.com>
> wrote:
>
>> Hi Gagan,
>>
>> I need to start another discussion about it, but I had an offline
>> discussion with Suresh about auto-scaling. I will start another thread
>> about this topic too.
>>
>> Regards
>> Lahiru
>>
>>
>> On Wed, Jun 11, 2014 at 4:10 PM, Gagan Juneja <gagandeepjuneja@gmail.com>
>> wrote:
>>
>> > Thanks Lahiru for pointing to nice library, added to my dictionary :).
>> >
>> > I would like to know how are we planning to start multiple servers.
>> > 1. Spawning new servers based on load? Some times we call it as auto
>> > scalable.
>> > 2. To make some specific number of nodes available such as we want 2
>> > servers to be available at any time so if one goes down then I need to
>> > spawn one new to make available servers count 2.
>> > 3. Initially start all the servers.
>> >
>> > In scenario 1 and 2 zookeeper does make sense but I don't believe
>> existing
>> > architecture support this?
>> >
>> > Regards,
>> > Gagan
>> > On 12-Jun-2014 1:19 am, "Lahiru Gunathilake" <glahiru@gmail.com> wrote:
>> >
>> >> Hi Gagan,
>> >>
>> >> Thanks for your response. Please see my inline comments.
>> >>
>> >>
>> >> On Wed, Jun 11, 2014 at 3:37 PM, Gagan Juneja <
>> gagandeepjuneja@gmail.com>
>> >> wrote:
>> >>
>> >>> Hi Lahiru,
>> >>> Just my 2 cents.
>> >>>
>> >>> I am big fan of zookeeper but also against adding multiple hops in the
>> >>> system which can add unnecessary complexity. Here I am not able to
>> >>> understand the requirement of zookeeper may be I am wrong because of
>> less
>> >>> knowledge of the airavata system in whole. So I would like to discuss
>> >>> following point.
>> >>>
>> >>> 1. How it will help us in making system more reliable. Zookeeper is
>> not
>> >>> able to restart services. At max it can tell whether service is up or
>> not
>> >>> which could only be the case if airavata service goes down gracefully
>> and
>> >>> we have any automated way to restart it. If this is just matter of
>> routing
>> >>> client requests to the available thrift servers then this can be
>> achieved
>> >>> with the help of load balancer which I guess is already there in
>> thrift
>> >>> wish list.
>> >>>
>> >> We have multiple thrift services and currently we start only one
>> instance
>> >> of them and each thrift service is a stateless service. To keep the
>> high
>> >> availability we have to start multiple instances of them in production
>> >> scenario. So for clients to get an available thrift service we can use
>> >> zookeeper znodes to represent each available service. There are some
>> >> libraries which is doing similar[1] and I think we can use them
>> directly.
>> >>
>> >>> 2. As far as registering of different providers is concerned do you
>> >>> think for that we really need external store.
>> >>>
>> >> Yes I think so, because its light weight and reliable and we have to do
>> >> very minimal amount of work to achieve all these features to Airavata
>> >> because zookeeper handle all the complexity.
>> >>
>> >>> I have seen people using zookeeper more for state management in
>> >>> distributed environments.
>> >>>
>> >> +1, we might not be the most effective users of zookeeper because all
>> of
>> >> our services are stateless services, but my point is to achieve
>> >> fault-tolerance we can use zookeeper and with minimal work.
>> >>
>> >>>  I would like to understand more how can we leverage zookeeper in
>> >>> airavata to make system reliable.
>> >>>
>> >>>
>> >> [1]https://github.com/eirslett/thrift-zookeeper
>> >>
>> >>
>> >>
>> >>> Regards,
>> >>> Gagan
>> >>> On 12-Jun-2014 12:33 am, "Marlon Pierce" <marpierc@iu.edu> wrote:
>> >>>
>> >>>> Thanks for the summary, Lahiru. I'm cc'ing the Architecture list
for
>> >>>> additional comments.
>> >>>>
>> >>>> Marlon
>> >>>>
>> >>>> On 6/11/14 2:27 PM, Lahiru Gunathilake wrote:
>> >>>> > Hi All,
>> >>>> >
>> >>>> > I did little research about Apache Zookeeper[1] and how to
use it
>> in
>> >>>> > airavata. Its really a nice way to achieve fault tolerance
and
>> >>>> reliable
>> >>>> > communication between our thrift services and clients. Zookeeper
>> is a
>> >>>> > distributed, fault tolerant system to do a reliable communication
>> >>>> between
>> >>>> > distributed applications. This is like an in-memory file system
>> which
>> >>>> has
>> >>>> > nodes in a tree structure and each node can have small amount
of
>> data
>> >>>> > associated with it and these nodes are called znodes. Clients
can
>> >>>> connect
>> >>>> > to a zookeeper server and add/delete and update these znodes.
>> >>>> >
>> >>>> >   In Apache Airavata we start multiple thrift services and
these
>> can
>> >>>> go
>> >>>> > down for maintenance or these can crash, if we use zookeeper
to
>> store
>> >>>> these
>> >>>> > configuration(thrift service configurations) we can achieve
a very
>> >>>> reliable
>> >>>> > system. Basically thrift clients can dynamically discover available
>> >>>> service
>> >>>> > by using ephemeral znodes(Here we do not have to change the
>> generated
>> >>>> > thrift client code but we have to change the locations we are
>> invoking
>> >>>> > them). ephemeral znodes will be removed when the thrift service
>> goes
>> >>>> down
>> >>>> > and zookeeper guarantee the atomicity between these operations.
>> With
>> >>>> this
>> >>>> > approach we can have a node hierarchy for multiple of airavata,
>> >>>> > orchestrator,appcatalog and gfac thrift services.
>> >>>> >
>> >>>> > For specifically for gfac we can have different types of services
>> for
>> >>>> each
>> >>>> > provider implementation. This can be achieved by using the
>> >>>> hierarchical
>> >>>> > support in zookeeper and providing some logic in gfac-thrift
>> service
>> >>>> to
>> >>>> > register it to a defined path. Using the same logic orchestrator
>> can
>> >>>> > discover the provider specific gfac thrift service and route
the
>> >>>> message to
>> >>>> > the correct thrift service.
>> >>>> >
>> >>>> > With this approach I think we simply have write some client
code in
>> >>>> thrift
>> >>>> > services and clients and zookeeper server installation can
be done
>> as
>> >>>> a
>> >>>> > separate process and it will be easier to keep the Zookeeper
server
>> >>>> > separate from Airavata because installation of Zookeeper server
>> little
>> >>>> > complex in production scenario. I think we have to make sure
>> >>>> everything
>> >>>> > works fine when there is no Zookeeper running, ex:
>> >>>> enable.zookeeper=false
>> >>>> > should works fine and users doesn't have to download and start
>> >>>> zookeeper.
>> >>>> >
>> >>>> >
>> >>>> >
>> >>>> > [1]http://zookeeper.apache.org/
>> >>>> >
>> >>>> > Thanks
>> >>>> > Lahiru
>> >>>>
>> >>>>
>> >>
>> >>
>> >> --
>> >> System Analyst Programmer
>> >> PTI Lab
>> >> Indiana University
>> >>
>> >
>>
>>
>> --
>> System Analyst Programmer
>> PTI Lab
>> Indiana University
>>
>
>
>
> --
> Best Regards,
> Shameera Rathnayaka.
>
> email: shameera AT apache.org , shameerainfo AT gmail.com
> Blog : http://shameerarathnayaka.blogspot.com/
>



-- 
Supun Kamburugamuva
Member, Apache Software Foundation; http://www.apache.org
E-mail: supun06@gmail.com;  Mobile: +1 812 369 6762
Blog: http://supunk.blogspot.com

Mime
View raw message