Goals

Checklist

•  User stories documented (Albert/Vinisha) 
•  User stories reviewed (Nitin)
•  Design documented (AlbertShankar/VinishaKashif)
•  Design reviewed (Terence/Andreas)
•  Feature merged ()
•  Examples and guides ()
•  Integration tests () 
•  Documentation for feature ()
•  Blog post

Use Cases

1. A pipeline developer wants to create a pipeline that has several configuration settings that are not known at pipeline creation time, but that are set at the start of the each pipeline run. 
   1. A pipeline developer wants to create a pipeline that reads from a database source and writes to a table sink. He wants to configure the name of the database table and name of the table sink on a per run basis and he gives those values as input before starting the run.  
2. A pipeline developer wants to create a pipeline with a custom action at the start of the run. The custom action based on some logic provides the name of the database to use as source and the name of the table to write in sink. The next stage in pipeline uses this information to read from the appropriate database source and write to the table sink.  
   

User Stories

1. As a pipeline developer, I want to be able to configure a plugin property to some value that will be substituted each run based on the runtime arguments.
2. As a pipeline operator, I want to be able to set arguments for the entire pipeline that will be used for substitution.
3. As a pipeline operator, I want to be able to set arguments for a specific stage in the pipeline that will be used for substitution.
4. As a plugin developer, I want to be able to write a code that is executed at the start of the pipeline and sets arguments for the rest of the run.

Design

Macros Syntax

ExpandedFunction Syntax : 
${macro-typemacroFunction(macro)}
 
Property Shorthandlookup notationsyntax:
${macro}
 
Example Usage: 
${runtime-argument(hostname)) - get hostname from runtime arguments
${wf-token(hostname)) - get hostname from
workflow token
${secure(access_keyaccessKey))} - get access key from secure store 
${function_time(time_format))logicalStartTime(timeFormat)} - apply time function on the time_formattimeFormat provided and use the value. 
 
The Default (short-handshortHand) usage will readsubstitute fromarguments runtimeusing arguments,the havingfollowing anprecedence:
expandedCustom notationAction givesWorkflow-Token user> optionRuntime forArguments using> moreStored macroPreferences
types. 
Examples :
ipConfig : ${hostname}:${port}
JDBC connection string : jdbc:${jdbc-plugin}://${hostname}:${sql-port}/${db-name}
 

The "function_time" macro function uses the logical start time of a run to perform the substitution. This is an example of a macro function that is not just a key-value lookup but allows for extra logic to be performed before a value is returned. For now, the implementation will only support the following macro functions: runtime-arguments, workflow tokens, and function_time. Once the secure store API is available, it will also support secure store. In the future, we can see if we will allow developers to create custom macro functions (similar to function_time(...)).

"stages": [
    {
        "name": "Database",
        "plugin": {
            "name": "Database",
            "type": "batchsource",
            "properties": {
				...
                "user": "${username}",
                "password": "${secure(sql-password)}",
     
Using the expanded syntax allows additional logic to be applied to the macro arguments through a macro function.
Escaping can be supported using the \ (backslash) character (e.g. \${hostname} will not be substituted)
 
Nested macros:
if a macro contains another macro, Example : ${secure(${user-name})} 
In the above example, we want to lookup the user-name in properties first, then use secure store to get the key/password for that user-name. this final key/password will be used for that field. 

The shorthand notation supports retrieval precedence to limit the exposure of underlying workflow-tokens and runtime-arguments to pipeline operators. The "functionTime" macro function uses the logical start time of a run to perform the substitution. This is an example of a macro function that is not just a key-value lookup but allows for extra logic to be performed before a value is returned. For now, the implementation will only support the following macro functions: runtime-arguments. Once the secure store API is available, it will also support secure store. In the future, we can see if we will allow developers to create custom macro functions (similar to functionTime(...)).

Notes:

• The current implementation for macro substitution supports recursive expansion. That is, if a macro such as ${address} expands to ${hostname}:${port}, then ${hostname} and ${port} will be evaluated. However, this can lead to an infinite loop from circular macros, so we can add a maximum depth for expansion.

"stages": [
    {
          "jdbcPluginNamename": "jdbcDatabase",
    
           "jdbcPluginTypeplugin": "${jdbc-type}",
                "connectionStringname": "jdbc:${jdbc-type}//${hostname}:${port}/${db-name}",
  Database",
             "importQuerytype": "selectbatchsource",
* from ${table-name};"          "properties":   }
        }{
				...
      },     {         "nameuser": "Table${username}",
        "plugin": {             "namepassword": "Table${secure(sql-password)}",
                "typejdbcPluginName": "batchsinkjdbc",
                "jdbcPluginType": "${jdbc-type}",
                "connectionString": "jdbc:${jdbc-type}//${hostname}:${port}/${db-name}",
                "propertiesimportQuery": {"select * from ${table-name};"
            }
"schema": "{\"type\":\"record\",\"name\":\"etlSchemaBody\",       }
    },
    \"fields\":[{\"name\":\"name\",\"type\":\"string\"},
 {
        "name": "Table",
        "plugin": {
              {\"name\":\ "age\Table",\
            "type\":\ "int\batchsink"},{\"name\":\"emp_id\",\"type\":\"long\"}]}",,                        "name": "${table-name}",               
 "schema.row.field": "name"          "properties": {
 }         }     }
]

Hydrator Plugin Changes

Currently when we deploy a pipeline,  configurePipeline is called on each plugin. we perform few validations in the configure stage, specifically for schema strings, syntax for scripts, etc. In some Plugins we also create a dataset if the dataset doesn't already exist. 

The dataset to write to can be macro-substituted, so we have to defer dataset creation to prepareRun rather than doing this in the configure stage. 

Deferring dataset creation in prepareRun will require adding a new method to BatchContext. 

@Beta
public interface BatchContext extends DatasetContext, TransformContext {

// new method
void createDataset(String datasetName, String typeName, DatasetProperties properties);
 
// existing methods
long getLogicalStartTime();

/**
 * Returns runtime arguments of the Batch Job.
 *
 * @return runtime arguments of the Batch Job.
 */
Map<String, String> getRuntimeArguments();

/**
 * Updates an entry in the runtime arguments.
 *
 * @param key key to update
 * @param value value to update to
 * @param overwrite if {@code true} and if the key exists in the runtime arguments, it will get overwritten to
 *                  the given value; if {@code false}, the existing value of the key won't get updated.
 */
void setRuntimeArgument(String key, String value, boolean overwrite);

/**
 * Returns the hadoop job.
 * @deprecated this method will be removed.
 */
@Deprecated
<T> T getHadoopJob();
...
}

Currently if a stream given in stream source or table given in table source doesn't exist, we create a new stream/table. We want to allow table creation as we want to create external dataset for sources, but disallow stream creation, so we are adding only createDataset to the BatchContext.

PluginConfigurer can be made not to extend DatasetConfigurer later as we no longer want to allow creating a dataset in configure.

However there are certain fields which are used to determine the schema in the plugin and those cannot be macro-substituted as schema validation is essential during configure time and we want to disallow macro usage for them. 

Platform Level Substitution:

Plugins can use an "@Macro" annotation to specify if a plugin field can be a macro and also provides a configure-value to use at configure time to instantiate the plugin.  

When a plugin instance is instantiated at configure time, macros cannot be substituted as the values to substitute have not been specified yet. By default, macros will be disabled for properties. This is to prevent new plugin developers from having to worry about undefined behavior if they did not consider or are not familiar with macros.

public class TableSinkConfig extends PluginConfig {
  @Name(Properties.Table.NAME)
  @Description("Name of the table "schema": "{\"type\":\"record\",\"name\":\"etlSchemaBody\",
                \"fields\":[{\"name\":\"name\",\"type\":\"string\"},
                {\"name\":\"age\",\"type\":\"int\"},{\"name\":\"emp_id\",\"type\":\"long\"}]}",
                "name": "${table-name}",
                "schema.row.field": "name"
            }
        }
    }
]

CDAP API Changes

Macro Annotation:

Plugins can use an "@Macro" annotation to specify if a plugin field can be a macro.  

When a plugin instance is instantiated at configure time, macros cannot be substituted as the values to substitute have not been specified yet. By default, macros will be disabled for properties. This is to prevent new plugin developers from having to worry about undefined behavior if they did not consider or are not familiar with macros.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
/**
 * Annotation for a plugin field to specify if it can support macro
 */
public @interface Macro {
}

/**
 * Contains information about a property used by a plugin.
 */
@Beta
public class PluginPropertyField {

  private final String name;
  private final String description;
  private final String type;
  private final boolean required;
  // returns true if this field can accept macro
  private final boolean isMacro;
  ...
}

Example Macro Usage in Plugin:

public class TableSinkConfig extends PluginConfig {
  @Name(Properties.Table.NAME)
  @Description("Name of the table. If the table does not already exist, one will be created.")
  // The name of the table can be specified by a runtime macro, by default macros are disabled for fields.
  @Macro 
  private String name;

  @Name(Properties.Table.PROPERTY_SCHEMA)
  @Description("schema of the table as a JSON Object. If the table does not already exist, one will be " +
    "created.") with this //schema, Thewhich namewill ofallow the table canto be specified by a runtime macro, by default macros are disabled for fields.
  @Macro(enabled=true) explored through Hive. If no schema is given, the " +
    "table created will not be explorable.")
  @Nullable
  private String nameschemaStr;

  @Name(Properties.Table.PROPERTY_SCHEMA_ROW_FIELD)
  @Description("schemaThe name of the tablerecord field asthat ashould JSONbe Object.used Ifas the tablerow doeskey notwhen alreadywriting exist,to one will be " +the table.")
  private String  "created with this schema, which will allow the table to be explored through Hive. If no schema is given, the " +
    "table created will not be explorable.")
  @Nullable
  private String schemaStr;

  @Name(Properties.Table.PROPERTY_SCHEMA_ROW_FIELD)
  @Description("The name of the record field that should be used as the row key when writing to the table.")
  private String rowField;
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Macro {

  /**
   * Default status if macro is enabled.rowField;
}

PluginConfig Changes:

@Beta
public abstract class PluginConfig extends Config implements Serializable {

  /**
   * Returns the {@link PluginProperties}.
   */
  public final PluginProperties getProperties() {
    return properties;
  }
 
  /**
   * Returns false if the field is not annotated as a macro. If field is annotated as macro, 
   * the field value is checked if its a macro, based on the check it returns true/false.  
   */
  boolean DEFAULT_STATUSpublic =final false;boolean isMacro(String fieldName) {
/**    * Returns if macro is enabled. Default is 'false'...
   */
  boolean enabled() default DEFAULT_STATUS;

}
 

/**
 * Contains information about a property used by a plugin.
 */
@Beta
public class PluginPropertyField {

  private final String name;
  private final String description;
  private final String type;
  private final boolean required;
  // returns true if this field can accept macro
  private final boolean macroEnabled;
  ...
}

Notes

This will require a CDAP platform level change as its a new annotation.

PluginInstantiator has to understand if macro is enabled and set fields appropriately.. 

During configure time in the configurePipeline method, if a field is macro enabled, the property should not be validated as the macro has not been provided a substitutable value.

During runtime, PipelineInsantiator would get config fields and values to substitute and can use that information to substitute macro appropriately and return an instantiated plugin.

Custom Action Setting Config values:

One use case of the feature is to allow custom actions that run before a plugin to set macros. Custom actions can use workflow tokens to set values for field names.  

"plugin": {
	"name": "Database",
	"type": "batchsource",
	"properties": {
		"user": "${wf-token(username)}",
		"password": "${secure(sql-password)}",
		"jdbcPluginName": "jdbc",         
		"importQuery": "select * from ${wf-token(table-name)};"
	}
}

If pipeline builder wants to use a workflow token sent from a preceding custom action to be used as value for fields, then he uses the macro-type token in his fields as above.

Context has access to the workflow token and we should be able to use workflow tokens similar to runtime arguments for substitution.

Scoping:

Because macro-substitution is performed at the platform level, users that require scoping at the stage name level must do this manually. In our example config from a JDBC source to a table sink, there is a common macro "${table-name}", if the user wants to provide a different name for the table-name in Table Sink, he can manually do this:

This is more of the user creating unique argument keys as opposed to scoping.

Documentation Changes

Regardless of where the substitution occurs, the guidelines for creating Hydrator plugins would have to change. For existing plugins, any validation for properties that are macro-substitutable in configurePipeline must be moved to prepareRun (see reference section for specific plugins). 

Implementation Details

interface MacroContext {	
	/**
	 * Given the macro key, return the substituted value
     */ 
	String getValue(String macroKey);
}

Based on the macro type, one of the below MacroContext's will be used to get the value for macro. 
 
DefaultMacroContext implements MacroContext {
	Map<String, String> runtimeArguments;
	String getValue(String macroKey) {
		return runtimeArguments.get(macroKey);
	}
}

SecureMacroContext implements MacroContext {
	SecureStore secureStore;
	String getValue(String macroKey) {
		return secureStore.get(macroKey);
	}
}

RuntimeFunctionMacro implements MacroContext {	
	long logicalStartTime;
	Function<String, String> timezoneFunction;
	String getValue(String arguments) {
		return timezoneFunction.apply(arguments);
	}
} 
 

---------------------- 

Setting Hydrator runtime arguments using CDAP runtime arguments/preferences

CDAP preferences and runtime arguments will be used directly as Hydrator arguments. 

1.) Runtime arguments can be passed to hydrator pipeline in 2 ways:

1. Using Prepipeline-CustomActions:
   Prepipeline custom actions can set runtime arguments. For example, before running the pipeline, custom actions can copy local files to hdfs and set runtime arguments for input path for batchsource. In order to do that, we can expose setPreferences() and getPreferences() programmatic api for setting runtime arguments. These arguments can be passed to hydrator app using workflow token. 
2. Using Hydrator UI:
   For each stage, runtime arguments can be passed from hydrator UI using cdap REST endpoints for preferences/runtime arguments framework. 

2.) Hydrator app will substitute properties using Macro substitution for each ETLStage. Now, plugins, like SFTP, which need secure substitution using key management can use 'secure' prefix in the macro. Macro substitution should vary depending on prefix of the arguments. In case of secure key, macro can be '${secure(key)}', in case of value directly to be substituted, macro can be '${inputpath}' without any prefix. 

...

}
}

The method will return whether or not the property with the provided fieldName contains a macro at configure time. We don't want to force deferring macros to runtime in the case that a field is macroable but actually has no macro provided in its configuration. This allows optional checking of properties at configure time for simple pipelines.  

private final TableSinkConfig sinkConfig;
@Override
void configurePipeline(PipelineConfigurer pipelineConfigurer) {
  if (!sinkConfig.isMacro("name")) {
 	// create dataset if the datasetName field is not a macro
    pipelineConfigurer.createDataset(name, datasetType, DatasetProperties.builder().addAll(properties).build());
  }
  ...
}

Notes:

• To allow macro substitution of non-String properties, any properties configured with a macro will have a placeholder default value at configure time which is different from runtime.
• For primitive types, this would be Java's default value, Example: integer field will have a value of 0. objects, would be null.
• This is fine because we are exposing a method to check whether a field is a macro or not in pipelineConfigurer. so plugin developers can check at configure time if a field is macro before performing appropriate action using that field. 
• During runtime, macro fields will be substituted and plugin instance will have fields with substituted values.

@Beta
public interface PluginContext {
 
/**
 * Creates a new instance of a plugin. The instance returned will have the {@link PluginConfig} setup with
 * {@link PluginProperties} provided at the time when the
 * {@link PluginConfigurer#usePlugin(String, String, String, PluginProperties)} was called during the
 * program configuration time. If a plugin field has a macro, 
 * the parameter evaluator is used to evaluate the macro and the evaluated value is used for the plugin field.
 *
 * @param pluginId the unique identifier provide when declaring plugin usage in the program.
 * @param evaluator the macro evaluator that's used to evaluate macro for plugin field if macro is supported on those fields. 
 * @param <T> the class type of the plugin
 * @return A new instance of the plugin being specified by the arguments
 *
 * @throws InstantiationException if failed create a new instance
 * @throws IllegalArgumentException if pluginId is not found
 * @throws UnsupportedOperationException if the program does not support plugin
 */
<T> T newPluginInstance(String pluginId, MacroEvaluator evaluator) throws InstantiationException;

@Beta
interface MacroEvaluator {  
 
/**
 * lookup the property and return the value corresponding to the property.
 */ 
 String evaluate(String property);  
/**
 * Use the macro function and call the function with provided arguments, 
 * apply appropriate function or use properties in default case and return the evaluated value
 */ 
 String evaluate(String macroFunction, String... arguments);  
} 

@Beta
public interface BatchContext extends DatasetContext, TransformContext {

/**
 * create dataset identified by datasetName, typeName with properties.
 */
void createDataset(String datasetName, String typeName, DatasetProperties properties);

/**
 * return true if dataset with datasetName exists 
 */
boolean datasetExists(String datasetName);

...
}

@Override
public void prepareRun(BatchSinkContext context) {
  if (!context.datasetExists(config.getName())) {
    pipelineConfigurer.createDataset(config.getName(), ...);
  }
  // ...
}

interface MacroContext {	
	/**
	 * Given the macro key, return the substituted value
     */ 
	String getValue(String macroKey);
}

Based on the macro type, one of the below MacroContext's will be used to get the value for macro. 
 
DefaultMacroContext implements MacroContext {
	Map<String, String> runtimeArguments;
	String getValue(String macroKey) {
		return runtimeArguments.get(macroKey);
	}
}

SecureMacroContext implements MacroContext {
	SecureStore secureStore;
	String getValue(String macroKey) {
		return secureStore.get(macroKey);
	}
}

RuntimeFunctionMacro implements MacroContext {	
	long logicalStartTime;
	Function<String, String> timezoneFunction;
	String getValue(String arguments) {
		return timezoneFunction.apply(arguments);
	}
} 

...