[wildfly-dev] Subsystems to advertise implicit and optional dependencies to galleon

[Brian Stansberry]

On Fri, Nov 9, 2018 at 2:30 AM, Jean-Francois Denise <jdenise at redhat.com>
wrote:

> Hi,
>
> in the galleon project, in a context where we would not provision a
> complete server but just a subset required to run a given configuration,
> we have identified a need for subsystems to advertise to the galleon
> tooling some modules in addition to the modules galleon discover by
> traversing the module dependency tree.
>
> The first case is DeploymentProcessor injecting modules into the
> deployment units (implicit modules).
>
> The deployment injected ones are not required to be a dependency of the
> subsystem module, so galleon has the risk to miss some of them.
>
> As an example, in logging subsystem we have the following non optional
> injected modules :
> "org.jboss.logging",
> "org.apache.commons.logging",
> "org.apache.log4j",
> "org.slf4j",
> "org.jboss.logging.jul-to-slf4j-stub"
>
> Some of these modules are direct dependencies of logging subsystem, some
> others are indirect dependencies, others could be not present at all in
> the module dependency tree (eg: org.jboss.logging.jul-to-slf4j-stub).
>
> So we are thinking at solving this issue in 2 possible ways:
>
> 1) Mandate that all injected modules become dependencies of the
> subsystem module at the cost to load some useless modules at runtime.
>
> 2) Possibly better, make the subsystem to call
> RuntimeCapability.addAdditionalRequiredPackages (package name being
> module name) for each injected module. An existing capability or a new
> one  would have to be created.
>
> There is also the case of optional injected module dependencies (eg: ee
> subsystem org.glassfish.javax.el, org.eclipse.yasson, ...). We need to
> treat them differently. When one is provisioning a server using galleon
> he can choose to exclude some packages from the provisioned server.
> Optional packages can be excluded without making the provisioned state
> invalid (as opposed to required package that can't be excluded). These
> optional implicit dependencies are typical usage of this, they are not
> required by the deployment unit to properly operate.
>
> For these, we plan to use
> RuntimeCapability.addAdditionalOptionalPackages. We can't make them
> "optional" in JBoss module. When galleon provision a subset of the
> server we don't include all optional dependencies.
>
> This brings the case of provisioning of optional dependencies present in
> JBOSS module.xml.
>
> We have identified multiple kind of optional dependencies.
>
> 1) The optional dependencies that are referencing modules only in use
> when a feature is present in the configuration of the subsystem (eg: jmx
> subsystem optional dep on org.jboss.remoting-jmx due to
> <remoting-connector/>, remoting subsystem optional dep on
> io.undertow.core for <http-connector/>, elytron subsystem optional dep
> on org.picketbox for <jacc-policy>)
>
> In order to have these dependencies to be provisioned with the
> subsystem, we can attach thanks to
> RuntimeCapability.addAdditionalRequiredPackages the modules to the
> feature. When the feature is present in the configuration, the module is
> no more optional but required.
>
> 2) The optional dependencies that reference modules that are part of
> another subsystems and only use if this other subsystem is present (eg:
> org.jboss.as.jpa optional dep on org.jboss.as.ejb3,
> org.jboss.as.transactions optional dep on org.jboss.remoting). These
> ones are simply not taken into account
>
> 3)  The optional dependencies that reference modules that are not part
> of another subsystem (so are not provisioned by another source) but are
> only meaningful if the other subsystem is present. We call these ones
> "passive" (eg: org.jboss.as.weld optional dependency on
> org.jboss.as.weld.ejb|jpa|beanvalidation|webservices|transactions).
> "passive" are analyzed. If all their dependencies are present, then they
> are included. Some implicit optional dependencies can fall into this
> category (eg: org.jboss.jaxrs optional dep on
> org.jboss.resteasy.resteasy-validator-provider-11).
>
> The passive optional dependencies would be advertised with
> RuntimeCapability.addAdditionalPassiveOptionalPackages(optional
> dependency package name).
>
> So to summarize:
>
> - RuntimeCapability.addAdditionalRequiredPackages for all required
> implicit modules
>
> - RuntimeCapability.addAdditionalRequiredPackages to associate optional
> dependencies to a feature
>
> - RuntimeCapability.addAdditionalOptionalPackages for all optional
> implicit dependencies that are not passive
>
> - RuntimeCapability.addAdditionalPassiveOptionalPackages for all
> optional dependencies (implicit or not) that are passive
>

A good question Alexey raised is whether the capability is the right
concept for encapsulating this information.

In the end the key point is that the information ends up in the galleon
feature-spec. That's the thing that encapsulates the configuration elements
and the packages (i.e. fs content) that are needed to provide a feature.
It's the feature that needs the package. We generate the galleon feature
specs from our management model information. When in WF 13 we hit the first
must-implement use case for getting additional package info into a feature
spec I kind of arbitrarily picked 'RuntimeCapability' as the place to
record that. It was a reasonable enough choice for that one use case but
isn't great otherwise.

The alternative is to record this data in the ResourceDefinition, which is
the primary source of the data that's used in the feature spec generation.

The conceptual argument is a capability is all about a named provider of a
contract that other elements of the server can rely on; e.g. some MSC
Service with a particular value type that will be exposed.  But this
additional package stuff isn't really about that contract, it's about other
things that will be done that likely are not relevant to other elements of
the system.

A hint of a design smell would be if we end up creating RuntimeCapability
instances for no other reason than to record this additional package
information. Something I could see happening with this logging case you
mentioned at the start.

I don't think ResourceDefinition has this problem.


> Is it something that subsystems owner would be ready to put in place to
> help galleon in this task? It would require a bit of analysis of the
> dependencies of your modules but the gain could be quite important.


Please don't let my point above derail consideration of this question.  Use
of ResourceDefinition vs RuntimeCapability is a relatively small detail.

Some
> early experimentation of this has shown a big reduction of the server
> filesystem footprint (web server + cdi has been reduced from 156MB to
> 46MB). The runtime memory usage reduction is not that big, but less
> modules being loaded we have a gain.
>
> Thanks for reading.
>
> JF
>
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-- 
Brian Stansberry
Manager, Senior Principal Software Engineer
Red Hat
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