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What CDAP platform provides:

API used by apps for logging the debug data

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This document explains the separation of responsibilities between CDAP platform and Applications. 

CDAP Platform

1. Java API: CDAP platform provides two sets of java API. External api is used by CDAP applications to interact with the preview system and internal api is used by preview REST handler.

   1. API to be used by applications:

      1. Get the instance of DebugLogger from program context. For example MapReduceContext will be updated to add new method as - 

         Code Block
         language java
         /** * MapReduce job execution context. */ public interface MapReduceContext ... { /** * Return the DebugLogger * @param loggerName the name of the logger using which the debug information will be logged */ DebugLogger getLogger(String loggerName); }

      2. Use DebugLogger to log the useful information.

         Code Block
         language java
         /** * Interface used by the CDAP applications to log the debug data. */ public interface DebugLogger { /** * Logs the data at INFO level. Multiple values can be logged against the same property. * @param propertyName the the name of the property * @param propertyValue the value associated with the property */ void info(String propertyName, Object propertyValue); /** * Return the name of the logger instance. */ String getName(); /** * Returns {@code true} if application is running in debug mode otherwise false is returned. */ boolean isEnabled(); }   /** * DebugLoggerFactory will be injected in the Program context classes. This may not be directly used by Applications. */ public interface DebugLoggerFactory { /** * Get the {@link DebugLogger} used to log the debug data. * @param loggerName the name of the logger with which the log data to be associated * @return the instance of the DebugLogger */ DebugLogger getLogger(String loggerName); }

   2. API to be used by REST handler: PreviewHttpHandler will be responsible for handling the REST calls (details below). This REST handler will also interact with the preview system through API exposed by PreviewManager. Note that this is internal API.

      Code Block
      language java
      /** * Interface used to start preview and also retrieve the information associated with a preview. */ public interface PreviewManager { /** * Start the program in preview mode. * @param namespaceId the id of the namespace * @param request the request for the preview. This includes details about artifact, application configs, and preview configurations used by CDAP(details below) * @return the unique {@link PreviewId} generated for the preview run * @throws Exception if there were any error during starting */ ApplicationId start(NamespaceId namespaceId, AppRequest<?> request) throws Exception; /** * Get the status for the specified {@link ApplicationId}. * @param preview the id of the preview for which status is to be returned * @return the status associated with the preview * @throws NotFoundException if the preview is not found */ PreviewStatus getStatus(ApplicationId preview) throws NotFoundException; /** *

   Returns

   1. Stop

   {@code

   1. the

   true}

   1. preview

   if

   1. identified

   application

   1. by

   is

   1. preview.

   running
   in
   debug mode otherwise false is returned.

   1. * @param preview id of the preview *

   /

   1. @throws Exception

   boolean isEnabled(); /** * Get the {@link DebugLogger} used to log the debug data. * @param loggerName the name of the logger with which the log data to be associated

   1. if the preview is not found or if there were any error during stop */ void stop(ApplicationId previewId) throws Exception; /** * Get the list of loggers in this preview. *

   @return

   1. @param

   the

   1. preview

   instance

   1. id of the

   DebugLogger

   1. preview *

   /

   1. @return the

   DebugLogger getLogger(String loggerName); } /** * Interface used by the CDAP applications to log the debug data. */ public interface DebugLogger {

   1. {@link List} of list of loggers for a given preview * @throws NotFoundException if the previewId is not found */ List<String> getLoggers(ApplicationId previewId) throws NotFoundException; /** *

   Logs

   1. Get the data

   at

   1. associated

   INFO

   1. with

   level.

   1. the

   Multiple

   1. specified

   values

   1. logger

   can

   1. name

   be logged

   1. of

   against

   1. the

   same property

   1. preview. * @param

   propertyName

   1. preview

   the

   1. id

   the name

   1. of the

   property

   1. preview * @param

   propertyValue

   1. loggerName the

   value

   1. name

   associated with

   1. of the

   property

   1. logger for which data

   */

   1. is to be

   void

   1. returned

   info(String
   propertyName,
   Object
   propertyValue);

   1. * @return the {@link Map}

   /**

   1. of property name to

   * Logs

   1. property value associated with the

   data

   1. given

   at

   1. logger

   DEBUG

   1. for

   level.

   1. a

   Multiple

   1. given

   values

   1. preview

   can
   be
   logged
   against

   1. *

   the

   1. @throws

   same

   1. NotFoundException

   property.

   1. if the preview is

   *

   1. not found

   @param
   propertyName
   the
   the

   1. */

   name
   of
   the

   1. Map<String,

   property

   1. List<String>> getData(ApplicationId preview, String

   *

   1. loggerName)

   @param

   1. throws

   propertyValue

   1. NotFoundException;

   the
   value
   associated
   with
   the
   property

   1. /** *

   /

   1. Get metric

   void

   1. associated

   debug(String propertyName, Object propertyValue);

   1. with the preview.

   /*

   1. * @param preview the

   *

   1. id

   Logs

   1. of the

   data

   1. preview

   at
   ERROR level. Multiple values can be logged against the same property.

   1. * @return the {@link Collection} of metrics emitted during the preview run *

   @param

   1. @throws

   propertyName

   1. NotFoundException

   the

   1. if the

   name

   1. previewId

   of

   1. is

   the

   1. not

   property

   1. found */

   @param
   propertyValue
   the

   1. Collection<MetricTimeSeries>

   value associated with the property

   1. getMetrics(ApplicationId preview) throws NotFoundException; /**

   */
   void

   1. *

   error(String propertyName, Object propertyValue);

   1. Get the logs for the preview.

   /

   1. *

   *

   1. @param

   *

   1. preview

   Return

   1. the

   name

   1. id of the

   logger

   1. preview

   instance.

   1. for which logs to

   */

   1. be fetched

   String
   getName();   /**

   1. * @return the logs

   1. *

   Return

   1. @throws

   the

   1. NotFoundException

   log

   1. if

   level

   1. the

   associated

   1. preview

   with

   1. is

   the

   1. not

   logger.

   1. found */

   DebugLogLevel

   1. List<LogEntry>

   getDebugLogLevel

   1. getLogs(ApplicationId preview) throws NotFoundException;

   1. }

   public

   1. //

   enum

   1. Instance

   DebugLogLevel

   1. of

   {

   1. the PreviewStatus is returned

   INFO,

   1. by the getStatus call

   ERROR,

   1. above. The details are

   WARN }REST endpoints

   1. To start a preview

      Code Block
      language java
      POST /v3/namespaces/{namespace-id}/preview where namespace-id is the nameas follows /** * Represents the state of the namespace Response will contain the CDAP generated unique preview-id which can be used further to get the preview data.

   2. To get the status of the preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/status where namespace-id is the name of the namespace preview-id is the id of the preview for which status is to be requested

   3. To get the data associated with the

      preview. */ public class PreviewStatus { public enum Status { RUNNING, COMPLETED, DEPLOY_FAILED, RUNTIME_FAILED }; Status previewStatus; @Nullable String failureMessage; // Represents the request with which the preview was started. AppRequest request; }

2. REST API exposed by platform:

   1. Start a preview

      Code Block
      language java
      GETPOST /v3/namespaces/{namespace-id}/previews/{preview-id}/loggers/{logger-id} where namespace-id is the name of the namespace Response will contain the CDAP generated unique preview-id is the id ofwhich can be used further to get the preview for which data is to be requesteddata.

   2. Get the status of preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/status where namespace-id is the name of the namespace loggerpreview-id is the uniqueid of namethe usedpreview tofor identifywhich the logger

   Platform specific CDAP configurations:

   1. status is to be requested

   2. Stop preview

      Code Block
      language java

   Application configuration will have preview related configurations which will be used by CDAP. Currently there are programId and programType configurations which will be used to identify the program to be executed as a part of preview.
   {
      "preview": {
         "programId": "MyProgram",
         "programType": "workflow",
         "logLevel": "info"
      }
   }

3. API used by CDAP platform to interact with the preview system:

   Code Block
   language java
   /** * Interface used to start preview and also retrieve the information associated with a preview. */ public interface PreviewManager { /** * Start the preview of an application config provided as an input. * @param namespaceId the id of * @param config the config for the preview * @return the unique {@link PreviewId} generated for the preview run * @throws Exception if there were any error during starting */ PreviewId start(NamespaceId namespaceId, String config) throws Exception; /** * Get the status for the specified {@link PreviewId}. * @param previewId the id of the preview for which status is to be returned * @return the status associated with the preview * @throws NotFoundException if the previewId is not found */ PreviewStatus getStatus(PreviewId previewId) throws NotFoundException; /** * Stop the preview identified by previewId. * @param previewId id of the preview * @throws Exception if the previewId is not found or if there were any error during stop */ void stop(PreviewId previewId) throws Exception; /** * Get the data associated with the preview. * @param previewId the id associated with the preview * @return the {@link Map} of logger name to properties associated with the logger for a given preview * @throws NotFoundException if the previewId is not found */ Map<String, Map<String, List<String>>> getData(PreviewId previewId) throws NotFoundException; /** * Get the data associated with the specified logger name of the preview. * @param previewId id of the preview * @param loggerName the name of the logger for which data is to be returned * @return the {@link Map} of property name to property value associated with the given logger for a given preview * @throws NotFoundException if the previewId is not found */ Map<String, List<String>> getData(PreviewId previewId, String loggerName) throws NotFoundException; /** * Get the data associated with the specified logger name of the preview. * @param previewId id of the preview * @param loggerName the name of the logger for which data is to be returned * @param logLevel the log level for which data to be retrieved * @return the {@link Map} of property name to property value associated with the given logger for a given preview * @throws NotFoundException if the previewId is not found */ Map<String, List<String>> getData(PreviewId previewId, String loggerName, DebugLogLevel logLevel) throws NotFoundException; /** * Get metric associated with the preview. * @param previewId the id of the preview * @return the {@link Collection} of metrics emitted during the preview run * @throws NotFoundException if the previewId is not found */ Collection<MetricTimeSeries> getMetrics(PreviewId previewId) throws NotFoundException; /** * Get the logs for the preview. * @param previewId the id of the preview for which logs to be fetched * @return the logs * @throws NotFoundException if the previewId is not found */ List<LogEntry> getLogs(PreviewId previewId) throws NotFoundException;  }

Application level capabilities:

1. Config changes which will be understood by the application. For hydrator following is an example of the application level preview configurations -

   Code Block
   language java
   Consider a simple pipeline: FTP -> CSVParser -> Table  { "artifact":{ "name":"cdap-data-pipeline", "version":"3.5.0-SNAPSHOT", "scope":"SYSTEM" }, "name":"MyPipeline", "config":{ "connections":[ { "from":"FTP", "to":"CSVParser" }, { "from":"CSVParser", "to":"Table" } ], "stages":[ { "name":"FTP", "plugin":{ "name":"FTP", "type":"batchsource", "label":"FTP", "artifact":{ "name":"core-plugins", "version":"1.4.0-SNAPSHOT", "scope":"SYSTEM" }, "properties":{ "referenceName":"myfile", "path":"/tmp/myfile" } }, "outputSchema":"{\"fields\":[{\"name\":\"offset\",\"type\":\"long\"},{\"name\":\"body\",\"type\":\"string\"}]}" }, { "name":"MyCSVParser", "plugin":{ "name":"CSVParser", "type":"transform", "label":"CSVParser", "artifact":{ "name":"transform-plugins", "version":"1.4.0-SNAPSHOT", "scope":"SYSTEM" }, "properties":{ "format":"DEFAULT", "schema":"{\"type\":\"record\",\"name\":\"etlSchemaBody\",\"fields\":[{\"name\":\"id\",\"type\":\"int\"},{\"name\":\"name\",\"type\":\"string\"}]}", "field":"body" } }, "outputSchema":"{\"type\":\"record\",\"name\":\"etlSchemaBody\",\"fields\":[{\"name\":\"id\",\"type\":\"int\"},{\"name\":\"name\",\"type\":\"string\"}]}" }, { "name":"MyTable", "plugin":{ "name":"Table", "type":"batchsink", "label":"Table", "artifact":{ "name":"core-plugins", "version":"1.4.0-SNAPSHOT", "scope":"SYSTEM" }, "properties":{ "schema":"{\"type\":\"record\",\"name\":\"etlSchemaBody\",\"fields\":[{\"name\":\"id\",\"type\":\"int\"},{\"name\":\"name\",\"type\":\"string\"}]}", "name":"mytable", "schema.row.field":"id" } }, "outputSchema":"{\"type\":\"record\",\"name\":\"etlSchemaBody\",\"fields\":[{\"name\":\"id\",\"type\":\"int\"},{\"name\":\"name\",\"type\":\"string\"}]}", "inputSchema":[ { "name":"id", "type":"int", "nullable":false }, { "name":"name", "type":"string", "nullable":false } ] } ], "appPreviewConfig": { "startStages": ["MyCSVParser"], "endStages": ["MyTable"], "useSinks": ["MyTable"], "outputs": { "FTP": { "data": [ {"offset": 1, "body": "100,bob"}, {"offset": 2, "body": "200,rob"}, {"offset": 3, "body": "300,tom"} ], "schema": { "type" : "record", "fields": [ {"name":"offset","type":"long"}, {"name":"body","type":"string"} ] } } } } } }   Note that "appPreviewConfig" section above is the application specific configurations which will be handled by the application.

2. Handling application level preview configurations: Preview configurations mentioned in the above section "appPreviewConfig" are application level and are required to handle by the application. 

End to End flow:

1. Request to the preview endpoint is given by user with the appropriate configurations. Note that the configurations will include the configs understood by CDAP and the configs understood by the app.

2. CDAP will generate unique preview id for this request which is returned to the user. User can then use this preview id further to query the data generated during the preview run.
3. Hydrator app will be configured based on the application configurations. For example for single stage preview configuration, we can add Worker in the app which will run the transform.
4. CDAP platform will determine which program in the application is require to execute based on the preview configurations provided for CDAP.
5. Based on the log level specified in the configurations, CDAP will write the preview data to the dataset.

Preview in Distributed Mode:

1. Preview service will run in a separate container. The container will be started when the master is started and will keep running.
2. Data generated by the preview system will be stored locally to the container. We can use the leveldb database similar to the standalone mode.
3. Instances of the container can be increased for scalability, however in that case since the preview data is local to the container, request for the preview data will need to be
   routed to the appropriate container which handled the preview request. One approach to achieve this is store the mappings in the HBase.
4. PreviewHttpHandler will be exposed through the preview container.
5. Logging for preview - Preview container will use the local log appender similar to the SDK. Do we need the ability to change the log levels for preview. For example should we allow running the application in preview mode using trace log level and running the application in normal mode using info level.
6. MetricsContext for preview - Querying metrics at the namespace level may not yield the entire namespace level data if the multiple instances of the preview containers are running.
7. Authorization: We store user privileges in Sentry. User is allowed to execute the program if he has EXECUTE permissions on it. This is currently managed by AuthorizationEnforcer. We can inject same instance in the Preview container so that reading and writing to the user datasets will be controlled by privileges in the sentry.
8. Impersonation: We store impersonation configurations in the Namespace meta store. NamespaceQueryAdmin is responsible for reading those configs. Preview container will need access to the instance of the query admin which will query the actual HBase table.
9. Deletion of the preview data: We will need the service which will clean up the preview data periodically. 

Open Questions:

1. Since we have separate instances of system tables for the preview, how would we know when the new namespace is created by the user? Should we share the NamespaceQueryAdmin?

...

1. 1. POST /v3/namespaces/{namespace-id}/previews/{preview-id}/stop where namespace-id is the name of the namespace preview-id is the id of the preview which is to be stopped

   2. Get the list of loggers in the preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/loggers where namespace-id is the name of the namespace preview-id is the id of the preview which is to be stopped

   3. Get the data associated with the preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/loggers/{logger-id} where namespace-id is the name of the namespace preview-id is the id of the preview logger-id is the id of the logger for which logs to be fetched

   4. Get the logs generated for the preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/logs where namespace-id is the name of the namespace preview-id is the id of the preview

   5. Get the metrics associated with the preview

      Code Block
      language java
      GET /v3/namespaces/{namespace-id}/previews/{preview-id}/metrics where namespace-id is the name of the namespace preview-id is the id of the preview

2. Preview specific configurations understood by CDAP: When preview is started, CDAP needs to know which program need to be executed. Following is a sample request json - 

   Code Block
   language java
   { "artifact":{ "name":"cdap-data-pipeline", "version":"3.5.0-SNAPSHOT", "scope":"SYSTEM" }, "name":"MyPipeline", "config":{ ..... application specific configurations }, "preview": { "programId": "MyProgram", "programType": "workflow" } }

   In the above config json, CDAP will look for "preview" key to figure out which program to be executed by preview.
   
   

Application responsibilities:

1. Application can use the API exposed by CDAP for getting the logger and logging the data.

2. Application specific configurations can be specified in the config section of the json. For example following are the preview related configurations for hydrator app - 

   Code Block
   language java
   { "artifact":{ "name":"cdap-data-pipeline", "version":"3.5.0-SNAPSHOT", "scope":"SYSTEM" }, "name":"MyPipeline", "config":{ "connections": { ... }, "stages": { ... }, "appPreviewConfig": { "startStages": ["MyCSVParser"], // stages from which pipeline execution is to be started "endStages": ["MyTable"], // stages till which pipeline need to be executed "useRealDatasets": ["FTP"], // list of datasets to be used from the real user space for READ only purpose "outputs": { "FTP": { "data": [ {"offset": 1, "body": "100,bob"}, {"offset": 2, "body": "200,rob"}, {"offset": 3, "body": "300,tom"} ] } } } }, "preview": { ..... CDAP specific preview configurations } }

3. Handling application level preview configurations: Preview configurations mentioned in the above section "appPreviewConfig" are application level and are required to handle by the application. More details TBD.