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From Neutron sharc <neutronsh...@gmail.com>
Subject Re: request for c++ api
Date Sat, 26 Mar 2016 03:25:27 GMT
Thank Zhen and Greg for your replies!

It sounds a feasible solution to have a local helix agent sit between
local c++ service and helix controller.

I want to point out that, we have proxies in front of the storage pool
to route user requests to different partitions.  When a master shard
is down, proxy failover to a slave (and promote a slave to master).

Based on Zhen's proposal,  it seems helix agent should also push the
state transitions to proxy to change its routing accordingly.

I have a few more questions:

1.  What's the current failure detection used by helix?  Who reports
errors to zookeeper?  Waiting for zookeeper timeout is not optimal for
us because we need fast fail over.

2.  Can a participant proactively push updates to zookeeper once
failure is detected, so controller can react fast. In our use case,
proxy usually is the first to detect errors because a request has
short timeout.

3.  are there any side effects if our c++ service peek on the
zookeeper data used by helix?

Any comments are highly appreciated.


On Fri, Mar 25, 2016 at 10:42 AM, Zhen Zhang <nehzgnahz@gmail.com> wrote:
> Hi Neutron, follow up on the HelixAgent idea. I think we can define two
> protocols:
> 1) PING
> You c/c++ service will implement an endpoint which accepts PING and returns
> OK. This is basically used for monitoring the liveness of your c/c++
> service.
> You c/c++ service will implement another endpoint which accepts
> STATE_TRANSITION(resource, partition, from_state, end_state), executes the
> actual state transition in your service, and returns OK or ERROR depending
> on the execution results. Note that state transitions are parallel, so you
> endpoint should be async. Actual parallelism can be configured.
> For the actual implementation, you can use tcp endpoint (eg.
> tcp://localhost:123456), or a restful endpoint (eg. http://localhost/ping
> for ping, and
> http://localhost/state_transition/?resource=..&partition=..&from_state=..&to_state=..
> for state transition)
> On the other hand, a java base HelixAgent will join the cluster as a
> participant. It keeps monitoring your service using the PING endpoint, and
> proxy the state transitions using the STATE_TRANSITION endpoint. Both
> endpoints can be configured on HelixAgent and we can provide a couple of
> default implementations like tcp or http.
> This idea should be straightforward to implement. Let us know if this works
> for you.
> Thanks,
> Jason
> On Mon, Mar 21, 2016 at 8:22 PM, Greg Brandt <brandt.greg@gmail.com> wrote:
>> Hey Neutron, have you considered Helix Agent?
>> http://helix.apache.org/0.7.1-docs/tutorial_agent.html
>> -Greg
>> On Mon, Mar 21, 2016 at 4:10 PM, Neutron sharc <neutronsharc@gmail.com>
>> wrote:
>>> Hi Helix team,
>>> Our distributed storage system consists of a storage pool partitioned
>>> into many shards. Each shard has a master and several slave replicas
>>> and we run replication to keep them synchronized.  We need a way to do
>>> automatic failover,  and resource rebalance. It seems helix can meet
>>> our needs. However our system is written in pure c/c++. Can you guys
>>> provide c++ api for participant and spectator so we can integrate
>>> helix into our system?  Thanks a lot!
>>> -neutron

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