Problem Statement

Currently, when developer wants to change the configuration of a cluster, say, create a region (or destroy an index, or update an async event queue) and have the change persisted in cluster configuration for incoming servers, there is no public api for him to do so. He will have to replicate the effort of the equivalent gfsh command to achieve the same effect. It would be nice if we can expose what these commands do to a public API.

Product Goals

User Goals

Create a more modular product to allow for easy extension and integration. The beneficiaries of this work are the developers working on different parts of the code such as Spring Data for Apache, Queries for Lucene index, storage for the JDBC connector, other Geode developers and anyone who wants to save settings to the Cluster Configuration Service.

What We Have Now:

From the current state of commands, It's not easy to extract a common interface for all the commands. And developers do not want to use gfsh command strings as a "make shift" api to call into the command. We are in need of a unified interface and a unified workflow for all the commands as well.

Proposal

Following the effort here, Public API for Retrieving/Updating Cluster Configuration, we already have a set of configuration objects derived from the cache xml schema. This would serve a common object that developers would use to configure the config instance first and then ask the cluster configuration service to persist it, either on the cache(create the real thing on an existing cache) or on the configuration service (persist the configuration itself). 

Pros and Cons:

Pros:

1. a common interface to call either on the locator/server/client side.
2. a common workflow to enforce behavior consistency.
3. Modularized implementation. The configuration object needs to implement the addition interfaces in order to be used in this API. This allows us to add functionality gradually and per function groups.

Cons:

1. Existing gfsh commands need to be refactored to use this API as well, otherwise we would have duplicate implementations.
2. When refactoring gfsh commands, some commands' behavior will change if they want to strictly follow this workflow, unless we add additional APIs for specific configuration objects.

Migration Strategy:

Our current commands uses numerous command options to configure the behavior of the commands. We will have to follow these steps to refactor the commands.

1. combine all the command options into one configuration objects inside the command itself.
   
2. have the command execution call the public API if the command conforms to the new workflow. In this step, the config objects needs to implement the ClusterCacheElement
3. If the command can't use the common workflow, make a special method in the api for that specific configuration object (we need to evaluate carefully. we don't want to make too many exceptions to the common workflow)
4. Once all the commands are converted using the ClusterConfiurationService API, All the command classes are just a a facade of collecting the options values, build the config object and call into the API. At this point, the command objects can only exist on the gfsh client.

Project Milestones

1. API is clearly defined
2. All commands are converted using this API
3. Command classes only exists on Gfsh client. The GfshHttpInvoker uses the rest api to call this ClusterConfigurationService with the configuration objects directly.