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https://issues.apache.org/jira/browse/STORM-561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14240180#comment-14240180
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P. Taylor Goetz commented on STORM-561:
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[~marz], I can see the utility of both approaches. I'll ask [~ncleung] to
correct me if I'm wrong, but I think this approach is largely aimed at
developers using the Java API, which is essentially a java library for
manipulating the thrift structures that make up a topology.
I think the pain point being addressed results from the standard pattern for
writing a topology *in java* (i.e. write a main() method, wire topology DAG,
switch for local/remote, etc.). Changes to the topology wiring require
recompiling/repackaging. I think what people are after is a way to
declaratively wire a topology without having to rebuild the jar. An example
case might be a shop that has lots of generic spouts/bolts that get wired into
different topologies, in which case it would be easier to have one jar and
external configuration files that define how they get wired into a specific
topology. Again, I'm specifically referring to the Java API that wraps the
thrift manipulation.
For interpreted/other languages, I agree that the way to go would be wrapper
library around the thrift API.
> Add ability to create topologies dynamically
> --------------------------------------------
>
> Key: STORM-561
> URL: https://issues.apache.org/jira/browse/STORM-561
> Project: Apache Storm
> Issue Type: Improvement
> Reporter: Nathan Leung
> Assignee: Nathan Leung
> Original Estimate: 336h
> Remaining Estimate: 336h
>
> It would be nice if a storm topology could be built dynamically, instead of
> requiring a recompile to change parameters (e.g. number of workers, number of
> tasks, layout, etc).
> I would propose the following data structures for building core storm
> topologies. I haven't done a design for trident yet but the intention would
> be to add trident support when core storm support is complete (or in parallel
> if there are other people working on it):
> {code}
> // fields value and arguments are mutually exclusive
> class Argument {
> String argumentType; // Class used to lookup arguments in
> method/constructor
> String implementationType; // Class used to create this argument
> String value; // String used to construct this argument
> List<Argument> arguments; // arguments used to build this argument
> }
> class Dependency {
> String upstreamComponent; // name of upstream component
> String grouping;
> List<Argument> arguments; // arguments for the grouping
> }
> class StormSpout {
> String name;
> String klazz; // Class of this spout
> List <Argument> arguments;
> int numTasks;
> int numExecutors;
> }
> class StormBolt {
> String name;
> String klazz; // Class of this bolt
> List <Argument> arguments;
> int numTasks;
> int numExecutors;
> List<Dependency> dependencies;
> }
> class StormTopologyRepresentation {
> String name;
> List<StormSpout> spouts;
> List<StormBolt> bolts;
> Map config;
> int numWorkers;
> }
> {code}
> Topology creation will be built on top of the data structures above. The
> benefits:
> * Dependency free. Code to unmarshal from json, xml, etc, can be kept in
> extensions, or as examples, and users can write a different unmarshaller if
> they want to use a different text representation.
> * support arbitrary spout and bolts types
> * support of all groupings, streams, via reflections
> * ability to specify configuration map via config file
> * reification of spout / bolt / dependency arguments
> ** recursive argument reification for complex objects
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