Page Comparison

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; /** * Stop the preview identified by preview. * @param preview id of the preview * @throws Exception 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. * @param preview id of the preview * @return the {@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; /** *

   Returns

   1. Get

   {@code

   1. the

   true}

   1. data

   if

   1. associated

   application

   1. with

   is

   1. the

   running

   1. specified

   in

   1. logger

   debug

   1. name

   mode

   1. of

   otherwise false is returned

   1. the preview. *

   /

   1. @param preview

   boolean isEnabled(); /** * Get the {@link DebugLogger} used to log the debug data.

   1. id of the preview * @param loggerName the name of the logger

   with

   1. for which

   the

   1. data

   log

   1. is

   data

   1. to be

   associated

   1. returned * @return the

   instance

   1. {@link Map} of

   the

   1. property name

   DebugLogger

   1. to property value associated

   */

   1. with the given

   DebugLogger

   1. logger

   getLogger(String loggerName); } /**

   1. for a given preview *

   Interface

   1. @throws

   used

   1. NotFoundException

   by

   1. if the

   CDAP

   1. preview

   applications

   1. is

   to

   1. not

   log

   1. found

   the
   debug
   data.

   1. */

   public
   interface
   DebugLogger

   1. Map<String,

   {

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

   /**

   1. String loggerName) throws NotFoundException;

   *
   Logs
   the
   data
   at

   1. /**

   INFO
   level.
   Multiple
   values

   1. *

   can

   1. Get

   be

   1. metric

   logged

   1. associated

   against

   1. with the

   same property

   1. preview. * @param

   propertyName

   1. preview the

   the

   1. id

   name

   1. of the

   property

   1. preview *

   @param propertyValue the value associated with the property

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

   /

   1. @throws NotFoundException

   void

   1. if

   info(String propertyName, Object propertyValue);

   1. the previewId is not found */

   **

   1. Collection<MetricTimeSeries>

   * Logs the data at DEBUG level. Multiple values can be logged against the same property

   1. getMetrics(ApplicationId preview) throws NotFoundException; /** * Get the logs for the preview. * @param

   propertyName

   1. preview the

   the

   1. id

   name

   1. of the

   property

   1. preview for which logs to

   *

   1. be

   @param

   1. fetched

   propertyValue
   the
   value
   associated

   1. *

   with

   1. @return the

   property

   1. logs *

   /

   1. @throws NotFoundException

   void debug(String propertyName, Object propertyValue);

   1. if the preview is not found */

   **
   * Logs the data at ERROR level. Multiple values can be logged against the same property. * @param propertyName the the name

   1. List<LogEntry> getLogs(ApplicationId preview) throws NotFoundException;  }   // Instance of the PreviewStatus is returned by the getStatus call above. The details are as follows /** * Represents the state of the

   property

   1. preview. */ public class

   *

   1. PreviewStatus

   @param

   1. {

   propertyValue
   the
   value

   1. public

   associated

   1. enum

   with

   1. Status

   the

   1. {

   property
   */

   1. RUNNING,

   void
   error(String
   propertyName

   1. COMPLETED,

   Object
   propertyValue);

   1. DEPLOY_FAILED,

   /**

   1. RUNTIME_FAILED

   *
   Return
   the
   name

   1. };

   of
   the
   logger
   instance.

   1. Status previewStatus;

   */

   1. @Nullable String

   getName()

   1. failureMessage;

    

   1. //

   **

   1. Represents the request

   *

   1. with

   Return

   1. which the

   log

   1. preview

   level associated with the logger

   1. was started.

   */ DebugLogLevel getDebugLogLevel()

   1. AppRequest request;

   1. }

   public enum DebugLogLevel { INFO, ERROR, WARN }REST endpoints

   1. To start a preview

      Code Block
      language java
      POST /v3/namespaces/{

2. REST API exposed by platform:

   1. Start a preview

      Code Block
      language java
      POST /v3/namespaces/{namespace-id}/previewpreviews where namespace-id is the name 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 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 Stop preview

      Code Block
      language java
      GETPOST /v3/namespaces/{namespace-id}/previews/{preview-id}/loggers/{logger-id}stop where namespace-id is the name of the namespace preview-id is the id of the preview for which data is to be requested loggerstopped

   4. 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 uniquename nameof usedthe tonamespace identify the logger

   Platform specific CDAP configurations:

   Code Block

   language	java

   Application
   configuration
   will
   have

   1. preview-id

   related

   1. is

   configurations

   1. the

   which

   1. id

   will

   1. of

   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": {

   1. the preview which is to be stopped

   2. 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

   "programId": "MyProgram", "programType": "workflow", "logLevel": "info" } }API used by CDAP platform to interact with the preview system:

   1. preview-id is the id of the preview logger-id is the id of the logger for which logs to be fetched

   2. Get the logs generated for the preview

      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

   1. 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

   2. 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

3. 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
   { * @param config"artifact":{ the config for the preview "name":"cdap-data-pipeline", * @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 is 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. "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.