[wildfly-dev] Graceful shutdown

[Stan Silvert]

Nice.

This is something we've been trying to do for more than a decade.   I 
was in a JBoss training about a year before I joined the company.  I 
remember Marc Fleury claiming that graceful shutdown was "almost working".

It looks like that this time you'll pull it off.

On 8/26/2014 12:19 AM, Stuart Douglas wrote:
> Hi all,
>
> The first graceful shutdown code has now gone into Wildfly upstream, and
> it should be possible to now start implementing this for all endpoints
> (at the moment it is only implemented for Undertow and remote EJB).
>
> Basically a server can be suspended by executing the :suspend operation
> in the CLI, and resumed using the :resume operation (there are
> corresponding options in domain mode as well that can be executed at
> domain, server group and server level). Servers can also be suspended by
> doing a graceful shutdown, which basically involves passing a timeout
> parameter to the :shutdown command (so :shutdown(timeout=60) will
> suspend the server, wait up to 60 seconds for all current requests to
> finish, then shut down).
>
>   From a code point of view there are two main constructs,
> org.jboss.as.server.suspend.SuspendController, which is notified of
> suspend events, and
> org.wildfly.extension.requestcontroller.RequestController, which deals
> with the common case of tracking active requests (and also allows a
> global request limit to be put in place as a form of overload protection).
>
> Subsystems that wish to use the SuspendController directly do this by
> registering ServerActivity callbacks, these callbacks notify the
> subsystem when the server is being suspended and resumed, and allow the
> subsystem to notify the server when the subsystem has suspended. This
> happens in two stages:
>
> - preSuspend() this is called first, and allows things like mod_cluster
> to notify the load balancer that the server is being suspended. During
> this phase the server processes requests normally.
>
> - suspend() this is called once the preSuspend() phase has completed,
> once suspend has started the subsystem should stop accepting requests,
> and notify the server once it considers itself fully suspended.
>
>
> Subsystems that wish to use RequestController do this by getting access
> to a ControlPoint, which is identified by (top level) deployment name +
> entry point name. When an external request starts the code calls
> beginRequest() and checks the return value to see if the request is
> allowed to proceed. If it is allowed then the code must call
> requestComplete() when it is finished.
>
> Note that this can only be used for external requests, or it can break
> already running code (e.g. @PreDestroy calls that are running when the
> server is suspended).
>
> Because the request controller tracks the deployment and entry point we
> may eventually use this information to also provide:
>
> - deployment level suspend (so we can do 'graceful undeploy')
> - entry point level suspend (e.g. suspend all web requests)
> - statistics on active requests by deployment/entry point
>
> Note that RequstController is a subsystem, and the request tracking does
> add a small amount of overhead. If the subsystem is removed then this
> overhead will disappear, however graceful shutdown will then not track
> active requests.
>
> All questions/comments are welcome, now that the core is in place I am
> going to start creating JIRA's for all the subsystem level integration work.
>
> Stuart
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