Option #3 (based on discussion with terence)

1) No new user level apps are deployed. Config store is used to store user drafts of hydrator apps.

2) REST endpoint 'configure', can accept partial config and return a config response with suggestions of values for fields in a plugin, exceptions if any during configuring the plugin. 

• user can choose a value from the suggestions for the field and call the configure again.
• user can look at exception, fix the issue with either the script or configuration and call configure again. 
• when all the required configs are provided and there aren't any exceptions, completionStatus would be set to true for the plugin.

Story 1 - Drafts

HTTP Request Type

Endpoint

Request Body

Response Status

Response Body

POST

#3 

Story 1 - Schema and field value suggestions : 

Plugin annotation @Endpoint: 

REST API :

POST : /namespaces/{namespace-id}/

artifacts/{

artifact-

name}/

{

"config": {...}

}

200 OK: config saved successfully

409 CONFLICT: draft-name already exists

500 Error: while saving the draft

PUT

/namespaces/{namespace-id}/configurations/{config-id}/

{

"config ": {...}

}

200 OK: config updated successfully

404 NOT Found : config doesn't exist already, cannot be updated.

500 Error while updating the config

GET

/namespaces/{namespace-id}/configurations/{config-id}/

200 return all the versions for the config identified by the config-name

404 config not found

500 error while getting config

[

{

"timestamp" : "...",

"config": {

"source" : {

   ....

 },

"transforms" : [...],

"sinks" [...]

"connections" : [..]

}

},

...

]

GET

/namespaces/{namespace-id}/configurations/{config-id}/versions/{version-number}

-1 -> latest version

200 return the versions for the config identified by the config-id and version-number

404 config with version found

500 error while getting config

{

"timestamp" : "...",

"config": {

"source" : {

   ....

 },

"transforms" : [...],

"sinks" [...]

"connections" : [..]

}

}

GET

/namespaces/{namespace-id}/configurations/

200 return the name of list of all saved configs

500 error

[
 "streamToTPFS",
 "DBToHBase",
  ...
]

versions/{artifact-version}/types/{plugin-type}
plugins/{plugin-name}/methods/{plugin-method}?scope={artifact-scope} 

 
Request-Body :  JSON -  fieldName to value mapping.
 
Response : 
200, Successful Response JSON string
404, Not Found, Plugin Specific Error Message (Example : DB, Table not found)
500, Error, Plugin Specific Error Message (Example : JDBC Connection error)
 
Description : In the request we refer to the plugin-artifact and not the parent artifact. we could use one of the available parent artifact. 

@Retention(RetentionPolicy.RUNTIME)
public @interface Endpoint {

  /**
   * Returns the endpoint.
   */
  String endpoint();
}

@Endpoint("listTables")
List<String> listTables(ListTableRequest request)

@Endpoint("getSchema")
Map<String, String> getSchema(SchemaRequest request)	

Story 2 - Drafts 

Configurations HTTP Handler:

Single HTTP Handler for unifying Console Setting Handler and Dashboards HTTP Handler. 

The ConsoleSettingsHttpHandler currently makes use of ConfigStore. It's however not name-spaced and has few other issues, it can be fixed and can be improved to store configs.

Along with pipeline drafts ConsoleSettingsHttpHandler also stores the following information currently:

 // create/update defaults this include user's plugin version preferences, etc.
 PUT : namespaces/{namespace-id}/defaults -d '@default.json' 
 GET : namespaces/{namespace-id}/defaults 

JAVA API - Config Store:

void create(String namespace, String type, Config config) throws ConfigExistsException;

void createOrUpdate(String namespace, String type, Config config);

void delete(String namespace, String type, String id) throws ConfigNotFoundException;

List<Config> list(String namespace, String type);

Config get(String namespace, String type, String id) throws ConfigNotFoundException; 

void update(String namespace, String type, Config config) throws ConfigNotFoundException;

// get a particular version of an entry. 
Config get(String namespace, String type, String id, int version) throws ConfigNotFoundException; 
// get all the versions of an entry.
Config getAllVersions(String namespace, String type, String id) throws ConfigNotFoundException; 
// delete all entries of specified type.
void delete(String namespace, String type) 

Open Questions :

1) ConfigStore stores the configs in "config.store.table", currently the table properties doesn't have versioning, drafts would need versioning, this would also need CDAP-upgrade to update properties for the existing dataset? 

2) rename ConsoleSettingsHttpHandler to ConfigurationsHttpHanlder ?

3) Dependent UI changes. 

Story 2 - Schema and field value suggestions : 

REST API:

Request-Method : POST

Request-Endpoint : /namespaces/{namespace-id}/apps/{app-id}/configure

Request-Body

{
    "artifact": {
        "name": "cdap-etl-batch",
        "scope": "SYSTEM",
        "version": "3.4.0-SNAPSHOT"
    },
    "name": "pipeline",
    "config": {
        "source": {
			     "name": "Stream",
                 "plugin": {
                    "name": "StreamSource",
                    "artifact": {
                        "name": "core-plugins",
                        "version": "1.3.0-SNAPSHOT",
                        "scope": "SYSTEM"
                    },
                    "properties": {
                        "format": "syslog",
                        "name": "test",
                        "duration": "1d"
                    }
                }
            },
         "sinks" : [{..}],
          "transform": [{..}, {...}]
        }
}

Response-Body

{
    "artifact": {
        "name": "cdap-etl-batch",
        "scope": "SYSTEM",
        "version": "3.4.0-SNAPSHOT"
    },
    "name": "pipeline",
    "config": {
        "source": {
				"name": "Stream",
                "plugin": {
                    "name": "StreamSource",
                    "artifact": {
                        "name": "core-plugins",
                        "version": "1.3.0-SNAPSHOT",
                        "scope": "SYSTEM"
                    },
                    "properties": {
                        "format": "syslog",
                        "name": "test",
                        "duration": "1d",
                        "suggestions" : [{ 
                             "schema" : [ 
                                 { 
								 	"ts" : "long", 
                                    "headers", "Map<String, String>", 
                                    "program", "string",
									"message": "string",
									"pid": "string"
						         }
						       ]
							}],
						"isComplete" : "false"
                  	}
                }
            },
         "sinks" : [{..}],
         "transform": [{..}, {...}]
        }
}

JAVA API 

PipelineConfigurable API Change

@Beta
public interface PipelineConfigurable {
  // change in return-type.
  ConfigResponse configurePipeline(PipelineConfigurer pipelineConfigurer) throws IllegalArgumentException; 
}

public class ConfigResponse {
 // list of suggestions for fields. 
 List<Suggestion> suggestions;
 // if there were any exception while executing configure 
 @Nullable
 String exception;
 // is the stage configuration complete ? 
 @DefaultValue("false")
 boolean isComplete;
}

public class Suggestion {
String fieldName;
// list of possible values for the fieldName
List<String> fieldValues; 
} 

@Beta
public interface ApplicationContext<T extends Config> {
  // existing
  T getConfig();
  // application will set a config response
  void setResponseConfig(T response);
  // get the response config
  T getResponseConfig();
}

Open Questions:

1) would having setResponseConfig and getResponseConfig ApplicationContext along with input config,  allow CDAP programs to set a config and read from other programs, would that be an issue?

2) Database's have information schema table, which has metadata information about column names and their types of tables.

• However we have recently removed tableName from DBSource plugin, so how would we figure out this information from just the query ? 
• how to get schema for complex queries involving multiple tables ? This would involve parsing query to understand fields and the tables they are from and then querying the information schema for the types. 

"Drafts", "Plugin Templates",  "Default versions"  and "Dashboards" are type of configurations specified as  "config-type" in the REST call.

The individual JSON-config or object would be identified by "object-id".

JAVA API - Config Store:

void create(String namespace, String type, Config config) throws ConfigExistsException;

void createOrUpdate(String namespace, String type, Config config);

void delete(String namespace, String type, String id) throws ConfigNotFoundException;

List<Config> list(String namespace, String type);

Config get(String namespace, String type, String id) throws ConfigNotFoundException; 

void update(String namespace, String type, Config config) throws ConfigNotFoundException;

// get a particular version of an entry. 
Config get(String namespace, String type, String id, int version) throws ConfigNotFoundException; 
// get all the versions of an entry.
List<Config> getAllVersions(String namespace, String type, String id) throws ConfigNotFoundException; 
 

Schema Propagation and Validation through backend - DryRuns:

POST : namespace/{namespace-id}/dry-run 

Request-Body : JSON Config.

Response-Body: 
JSON Config with additional fields in the plugin for output schema, 
exceptions in configuring pipeline stage, etc.  

User Stories (3.5.0)

1. For the hydrator use case, the backend app should be able to support hydrator related functionalities listed below:
2. query for plugins available for a certain artifacts and list them in UI
3. obtaining output schema of plugins provided the input configuration information
4. deploying pipeline and start/stop the pipeline
5. query the status of a pipeline run and current status of execution if there are multiple stages.
6. get the next schedule of run, ability to query metrics and logs for the pipeline runs.
7. creating and saving pipeline drafts
8. get the input/output streams/datasets of the pipeline run and list them in UI. 
9. explore the data of streams/datasets used in the pipeline if they are explorable. 
10. Add new metadata about a pipeline and retrieve metadata by pipeline run,etc.
11. delete hydrator pipeline
12. the backend app's functionalities should be limited to hydrator and it shouldn't be like a proxy for CDAP.  

Having this abilities will remove the logic in CDAP-UI to make appropriate CDAP REST calls, this encapsulation will simplify UI's interaction with the back-end and also help in debugging potential issues faster. In future, we could have more apps similar to hydrator app so our back-end app should define and implement generic cases that can be used across these apps and it should also allow extensibility to support adding new features. 

Generic Endpoints