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From kishore g <g.kish...@gmail.com>
Subject Re: General Architecture built around Helix
Date Mon, 24 Jun 2013 05:42:11 GMT
Hi Lance,

That a fairly simple fix. Will provide the fix tomorrow.

Kishore G

On Sun, Jun 23, 2013 at 2:18 PM, Lance Co Ting Keh <lance@box.com> wrote:

> Hi Kishore,
> Hope you are having a restful weekend. I was just wondering when I should
> normally expect the bug fix to go through?
> Thank you very much,
> Lance
> On Tue, Jun 18, 2013 at 1:36 PM, Lance Co Ting Keh <lance@box.com> wrote:
>> Thanks Kishore, here is the link to the bug:
>> https://issues.apache.org/jira/browse/HELIX-131
>> On Tue, Jun 18, 2013 at 9:13 AM, kishore g <g.kishore@gmail.com> wrote:
>>> My bad, i dint realize that you needed helixadmin to actually create the
>>> cluster.  Please file a bug, fix it quite simple.
>>> thanks,
>>> Kishore G
>>> On Tue, Jun 18, 2013 at 9:00 AM, Lance Co Ting Keh <lance@box.com>wrote:
>>>> Thanks Kishore. Would you like me to file a bug fix for the first
>>>> solution?
>>>> Also with the use of the factory, i get the following error message:
>>>> [error] org.apache.helix.HelixException: Initial cluster structure is
>>>> not set up for cluster: dev-box-cluster
>>>> Seems it did not create the appropriate zNodes for me. was there
>>>> something i was suppose to initialize before calling the factory?
>>>> Thank you
>>>> Lance
>>>> On Mon, Jun 17, 2013 at 8:09 PM, kishore g <g.kishore@gmail.com> wrote:
>>>>> Hi Lance,
>>>>> Looks like we are not setting the connection timeout while connecting
>>>>> to zookeeper in zkHelixAdmin.
>>>>> Fix is to change line 99 in ZkHelixAdmin.java   _zkClient = newZkClient(zkAddress);
>>>>> _zkClient = new ZkClient(zkAddress, timeout* 1000);
>>>>> Another workaround is to use HelixManager to get HelixAdmin
>>>>> manager = HelixManagerFactory.getZKHelixManager(cluster, "Admin",
>>>>> InstanceType.ADMINISTRATOR, zkAddress);
>>>>> manager.connect();
>>>>> admin= manager. getClusterManagmentTool();
>>>>> This will wait for 60 seconds before failing.
>>>>> Thanks,
>>>>> Kishore G
>>>>> On Mon, Jun 17, 2013 at 6:15 PM, Lance Co Ting Keh <lance@box.com>wrote:
>>>>>> Thank you kishore. I'll definitely try the memory consumption of
>>>>>> JVM per node.js server first. If its too much we'll likely do your
>>>>>> design but execute kills via the OS. This is to ensure no rogue servers.
>>>>>> I have a small implementation question. when calling new
>>>>>> ZkHelixAdmin, when it fails it retries again and again infinitely.
>>>>>> admin = new ZKHelixAdmin("")) is there a method I can override to
limit the
>>>>>> number of reconnects and just have it fail?
>>>>>> Lance
>>>>>> On Sun, Jun 16, 2013 at 11:56 PM, kishore g <g.kishore@gmail.com>wrote:
>>>>>>> Hi Lance,
>>>>>>> Looks good to me. Having a JVM per node.js server might add
>>>>>>> additional over head, you should definitely run this with production
>>>>>>> configuration and ensure that it does not impact performanace.
If you find
>>>>>>> it consuming too many resources, you can probably try this approach.
>>>>>>>    1. Have one agent per node
>>>>>>>    2. Instead of creating a separate helix agent per node.js,
>>>>>>>    can create a multiple participants within the same agent.
Each participant
>>>>>>>    will represents node.js process.
>>>>>>>    3. The monitoring of participant LIVEINSTANCE and killing
>>>>>>>    node.js process can be done by one of the helix agents. You
create an
>>>>>>>    another resource using leader-standby model. Only one helix
agent will be
>>>>>>>    the leader and it will monitor the LIVEINSTANCES and if any
Helix Agent
>>>>>>>    dies it can ask node.js servers to kill itself( you can use
http or any
>>>>>>>    other mechanism of your choice). The idea here is to designate
one leader
>>>>>>>    in the system to ensure that helix-agent and node.js act like
a pair.
>>>>>>> You can try this only if you find that overhead of JVM is
>>>>>>> significant with the approach you have listed.
>>>>>>> Thanks,
>>>>>>> Kishore G
>>>>>>> On Fri, Jun 14, 2013 at 8:37 PM, Lance Co Ting Keh <lance@box.com>wrote:
>>>>>>>> Thank you for your advise Santiago. That is certainly part
of the
>>>>>>>> design as well.
>>>>>>>> Best,
>>>>>>>> Lance
>>>>>>>> On Fri, Jun 14, 2013 at 5:32 PM, Santiago Perez <
>>>>>>>> santip@santip.com.ar> wrote:
>>>>>>>>> Helix user here (not developer) so take my words with
a grain of
>>>>>>>>> salt.
>>>>>>>>> Regarding 6 you might want to consider the behavior of
the node.js
>>>>>>>>> instance if that instance loses connection to zk, you'll
probably want to
>>>>>>>>> kill it too, otherwise you could ignore the fact that
the JVM lost the
>>>>>>>>> connection too.
>>>>>>>>> Regards,
>>>>>>>>> Santiago
>>>>>>>>> On Fri, Jun 14, 2013 at 6:30 PM, Lance Co Ting Keh <lance@box.com>wrote:
>>>>>>>>>> We have a working prototype of basically something
like #2 you
>>>>>>>>>> proposed above. We're using the standard helix participant,
and on the
>>>>>>>>>> @Transitions of the state model send commands to
node.js via Http.
>>>>>>>>>> I want to run you through our general architecture
to make sure
>>>>>>>>>> we are not violating anything on the Helix side.
As a reminder, what we
>>>>>>>>>> need to guarantee is that an any given time one and
only one node.js
>>>>>>>>>> process is in charge of a task.
>>>>>>>>>> 1. A machine with N cores will have N (pending testing)
>>>>>>>>>> processes running
>>>>>>>>>> 2. Associated with each of the N node processes are
also N Helix
>>>>>>>>>> participants (separate JVM instances -- reason for
this to come later)
>>>>>>>>>> 3. Separate helix controller will be running on the
machine and
>>>>>>>>>> will just leader elect between machines.
>>>>>>>>>> 4. The spectator router will likely be HAProxy and
thus a linux
>>>>>>>>>> kernel will run JVM to serve as Helix spectator
>>>>>>>>>> 5. The state machine for each will simply be ONLINEOFFLINE
>>>>>>>>>> (however i do get error messages that say that i
havent defined an OFFLINE
>>>>>>>>>> to DROPPED mode, i was going to ask you this but
this is a minor detail
>>>>>>>>>> compared to the rest of the architecture)
>>>>>>>>>> 5. Simple Bash script will serve as a watch dog on
each node.js
>>>>>>>>>> and helix participant pair. If any of the two are
"dead" the other process
>>>>>>>>>> must immediately be SIGKILLED, hence the need for
one JVM serving as Helix
>>>>>>>>>> Participant for every Node.js
>>>>>>>>>> 6. Each node.js instance sets a watch on /LIVEINSTANCES
>>>>>>>>>> to zookeeper as an extra safety blanket. If it finds
that it is NOT in the
>>>>>>>>>> liveinstances it likely means that its JVM participant
lost its connection
>>>>>>>>>> to Zookeeper, but the process is still running so
the bash script has not
>>>>>>>>>> terminated the node server. In this case the node
server must end its own
>>>>>>>>>> process.
>>>>>>>>>> Thank you for all your help.
>>>>>>>>>> Sincerely,
>>>>>>>>>> Lance
>>>>>>>>>> On Wed, Jun 12, 2013 at 9:07 PM, kishore g <g.kishore@gmail.com>wrote:
>>>>>>>>>>> Hi Lance,
>>>>>>>>>>> Thanks for your interest in Helix. There are
two possible
>>>>>>>>>>> approaches
>>>>>>>>>>> 1. Similar to what you suggested: Write a Helix
Participant in
>>>>>>>>>>> non-jvm language which in your case is node.js.
There seem to be quite a
>>>>>>>>>>> few implementations in node.js that can interact
with zookeeper. Helix
>>>>>>>>>>> participant does the following ( you got it right
but i am providing right
>>>>>>>>>>> sequence)
>>>>>>>>>>>    1. Create an ephemeral node under LIVEINSTANCES
>>>>>>>>>>>    2. watches /INSTANCES/<PARTICIPANT_NAME>/MESSAGES
node for
>>>>>>>>>>>    transitions
>>>>>>>>>>>    3. After transition is completed it updates
>>>>>>>>>>> Controller is doing most of the heavy lifting
of ensuring that
>>>>>>>>>>> these transitions lead to the desired configuration.
Its quite easy to
>>>>>>>>>>> re-implement this in any other language, the
most difficult thing would be
>>>>>>>>>>> zookeeper binding. We have used java bindings
and its solid.
>>>>>>>>>>> This is at a very high level, there are some
more details I have
>>>>>>>>>>> left out like handling connection loss/session
expiry etc that will require
>>>>>>>>>>> some thinking.
>>>>>>>>>>> 2. The other option is to use the Helix-agent
as a proxy: We
>>>>>>>>>>> added Helix agent as part of 0.6.1, we havent
documented it yet. Here is
>>>>>>>>>>> the gist of what it does. Think of it as a generic
state transition
>>>>>>>>>>> handler. You can configure Helix to run a specific
system command as part
>>>>>>>>>>> of each transition. Helix agent is a separate
process that runs along side
>>>>>>>>>>> your actual process. Instead of the actual process
getting the transition,
>>>>>>>>>>> Helix Agent gets the transition. As part of this
transition the Helix agent
>>>>>>>>>>> can invoke api's on the actual process via RPC,
HTTP etc. Helix agent
>>>>>>>>>>> simply acts as a proxy to the actual process.
>>>>>>>>>>> I have another approach and will try to write
it up tonight, but
>>>>>>>>>>> before that I have few questions
>>>>>>>>>>>    1. How many node.js servers run on each node
one or >1
>>>>>>>>>>>    2. Spectator/router is java or non java based
>>>>>>>>>>>    3. Can you provide more details about your
state machine.
>>>>>>>>>>> thanks,
>>>>>>>>>>> Kishore G
>>>>>>>>>>> On Wed, Jun 12, 2013 at 11:07 AM, Lance Co Ting
Keh <
>>>>>>>>>>> lance@box.com> wrote:
>>>>>>>>>>>> Hi my name is Lance Co Ting Keh and I work
at Box. You guys did
>>>>>>>>>>>> a tremendous job with Helix. We are looking
to use it to manage a cluster
>>>>>>>>>>>> primarily running Node.js. Our model for
using Helix would be
>>>>>>>>>>>> to have node.js or some other non-JVM library
be *Participants*,
>>>>>>>>>>>> a router as a *Spectator* and another set
of machines to serve
>>>>>>>>>>>> as the *Controllers *(pending testing we
may just run
>>>>>>>>>>>> master-slave controllers on the same instances
as the Participants) . The
>>>>>>>>>>>> participants will be interacting with Zookeeper
in two ways, one is to
>>>>>>>>>>>> receive helix state transition messages through
the instance of the
>>>>>>>>>>>> HelixManager <Participant>, and another
is to directly interact with
>>>>>>>>>>>> Zookeeper just to maintain ephemeral nodes
within /INSTANCES. Maintaining
>>>>>>>>>>>> ephemeral nodes directly to Zookeeper would
be done instead of using
>>>>>>>>>>>> InstanceConfig and calling addInstance on
HelixAdmin because of the basic
>>>>>>>>>>>> health checking baked into maintaining ephemeral
nodes. If not we would
>>>>>>>>>>>> then have to write a health checker from
Node.js and the JVM running the
>>>>>>>>>>>> Participant. Are there better alternatives
for non-JVM Helix participants?
>>>>>>>>>>>> I corresponded with Kishore briefly and he
mentioned HelixAgents
>>>>>>>>>>>> specifically ProcessMonitorThread that came
out in the last release.
>>>>>>>>>>>> Thank you very much!
>>>>>>>>>>>>  Lance Co Ting Keh

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