[jboss-jira] [JBoss JIRA] (AS7-4209) Automatic configuration of 'Initial_hosts' for a cluster using JGroups TCP-stack in domain mode

[Brian Stansberry (JIRA)]

    [ https://issues.jboss.org/browse/AS7-4209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679448#comment-12679448 ] 

Brian Stansberry commented on AS7-4209:
---------------------------------------

Matej Lazar had previously expressed interest in doing a DOMAIN_PING. That led to this exchange between myself and Bela Ban:


On 1/4/12 7:00 PM, Brian Stansberry wrote:
>
> There is no standard hook to allow arbitrary operation handlers on a
> server to communicate back to their own Host Controller or back to the
> master Host Controller. (The communication is possible; the
> infrastructure is just not exposed at the required level.) That's
> something we'll look at adding in 7.2 or later.
>
> That could be hacked around; i.e. the configuration for a DOMAIN_PING
> protocol could include the address/port of the master Host Controller.
> But that would be a horrible hack.


If we do this, then it should be an opaque blob stored by the master host controller under a given key; only the application would know how to interpret its contents.


> The only purpose of the master Host Controller in this would be to
> forward requests to the DOMAIN_PING service running on relevant servers
> to get the required data from them. The master Host Controller won't
> keep this information itself. It knows nothing about PingData or JGroups.


I don't think that's what Matej wanted to do: the master host controller (is this name final ?) has information about all JBoss instances running, so it would be a perfect starting point to query this information. In this sense, it could act as a replacement of GossipRouter. Of course, this makes sense only in environments where IP multicasting is not allowed, e.g. in clouds.


> All this said, I don't see this kind of PING implementation becoming a
> standard in the AS. For two reasons:
>
> 1) It introduces a dependency by the application server on the master
> Host Controller. Without that running master Host Controller, the
> JGroups channel will not behave properly.


Correct; discovery would not work, but normal operation (ie. message sending) would work, since it's not dependent on the master host controller being up.


>  Currently we have no such
> dependency. If the master HC is not running, the admin can't do some
> (but not all) administrative tasks. But it doesn't affect the ability of
> the applications servers to handle end user requests.


OK


> 2) We've been specifically warned by large users with experience running
> Websphere deployments about the danger of using the domain management
> communication pipelines for exchanging runtime information between
> services running on the application servers. Experience showed them that
> doing this quickly results in a flood of information between the servers
> that ends up degrading the ability to manage the servers.


OK


> I don't mean to sound overly negative here; this kind of thing is
> reasonable. It's just something that will take some thought and likely
> won't become the default behavior in the AS.

                
> Automatic configuration of 'Initial_hosts' for a cluster using JGroups TCP-stack in domain mode
> -----------------------------------------------------------------------------------------------
>
>                 Key: AS7-4209
>                 URL: https://issues.jboss.org/browse/AS7-4209
>             Project: Application Server 7
>          Issue Type: Feature Request
>          Components: Domain Management
>    Affects Versions: 7.1.1.Final
>         Environment: Server running in Domain mode
>            Reporter: Wolf-Dieter Fink
>            Assignee: Brian Stansberry
>              Labels: clustering, domain, jgroups
>
> It is complicated to keep the subsystem JGroups in sync if the tcp-stack is used in domain mode.
> All new servers that join/leave a clustered server group (configuration) must be added or removed by hand for the jgroup configuration.
> The domain server will receive the informations if a host-controller enrol and register server to a clustered server-group.
> So the configuration of the initial_hosts can be done automaticaly to avoid old entries which cause unnecessary checks and ensure that all active servers are known.

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