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From: Luca Burgazzoli <lburgazzoli@gmail.com>
Date: Mon, 29 May 2017 18:17:10 +0200
Message-ID: <CAMpNYoaf7J2LgohRgX4YPs-EO=NT2kuG529y-3HmdmkKkNXSHg@mail.gmail.com>
Subject: Re: Master/Leader RoutePolicy deprecation/fix
To: dev@camel.apache.org
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archived-at: Mon, 29 May 2017 16:17:17 -0000

Make sense, will raise the JIRAs soon to create the
LeaderElectionService which can the be leveraged by Dhiraj on
CAMEL-10320 and route policies.

---
Luca Burgazzoli


On Mon, May 29, 2017 at 5:48 PM, Nicola Ferraro <ni.ferraro@gmail.com> wrote:
> To me it seems that the route policy has everything needed to create
> master/slave routes. The autostartup=false flag can be forced on the
> "onInit" callback method as done in [3]. I think it's ok doing so, because
> it's responsibility of the policy to change standard behavior of the route.
>
> I've seen some leader election policies implemented in Camel and I think
> they are pretty similar. So I was thinking why we don't define just a
> single LeaderElectionRoutePolicy in Camel core. It will manage the burden
> of starting/stopping consumers (that is a delicate task and needs to take
> care of many details) and will be notified by a specific
> "LeaderElectionService" when gaining or losing the leadership (a callback
> method with a boolean argument). This way, each leader election "algorithm"
> needs just to implement the "LeaderElectionService" interface and just
> decide when he is the leader (and when he's no more), nothing else.
>
> This will also allow us to re-use leader election easily outside the
> purpose of starting/stopping camel routes. And it is a good thing for us
> developing Camel, but we can also expose leader election services directly
> to users, because creating a cluster-wide singleton service is not a
> trivial task, but Camel can to it easily.
>
> In conclusion, for me:
> - RoutePolicy wins over master
> - Better having just 1 generic LeaderRoutePolicy and a specific
> LeaderElectionService for each "algorithm"
>
>
> Nicola
>
> On Mon, May 29, 2017 at 4:57 PM, Claus Ibsen <claus.ibsen@gmail.com> wrote:
>
>> Hi
>>
>> Yeah the set auto startup=false seems like a good idea.
>>
>> On Mon, May 29, 2017 at 4:44 PM, Luca Burgazzoli <lburgazzoli@gmail.com>
>> wrote:
>> > Hello,
>> >
>> > I did a small review of the RoutePolicy we have for having one route
>> > master and one slave and all have an issue as they are invoked after
>> > the route is started so the consumer may have the time to consume some
>> > data before the policy kicks in [1].
>> >
>> > There is now a zookeeper-master component and some work is in in
>> > progress [2] in such area so wondering if we should deprecate such
>> > policies once [2] is done with or without fixing them.
>> >
>> > If we decide to fix them we could make the route to not auto start on
>> > policy initialization so then the policy could take care to start/stop
>> > the routes it is supposed to manage, an example of such behaviour can
>> > be see in my experimental branch [3] and in CuratorLeaderPolicy [4].
>> >
>> > Thoughts ?
>> >
>> > [1] https://github.com/apache/camel/blob/master/camel-core/
>> src/main/java/org/apache/camel/impl/RouteService.java#L213-L232
>> > [2] https://issues.apache.org/jira/browse/CAMEL-10320
>> > [3] https://github.com/lburgazzoli/apache-camel/blob/
>> route-policy/components/camel-infinispan/src/main/java/org/
>> apache/camel/component/infinispan/policy/InfinispanRoutePolicy.java
>> > [4] https://github.com/apache/camel/blob/master/components/
>> camel-zookeeper/src/main/java/org/apache/camel/component/zookeeper/policy/
>> CuratorLeaderRoutePolicy.java
>> >
>> > ---
>> > Luca Burgazzoli
>>
>>
>>
>> --
>> Claus Ibsen
>> -----------------
>> http://davsclaus.com @davsclaus
>> Camel in Action 2: https://www.manning.com/ibsen2
>>