Introduction

CDAP pipeline is composed of various plugins that can be configured by users as CDAP pipelines are being developed. While building CDAP pipelines, pipeline developer can provide invalid plugin configurations or schema. For example, the BigQuery sink plugin can have output schema which does not match with underlying BigQuery table. CDAP pipeline developer can use new validation endpoint to validate the stages before deploying the pipeline. In order to fail fast and for better user experience, validation endpoint should return all the validation errors from a given stage when this endpoint is called.

Data pipeline app exposes various error types for plugin validation. In future releases, new error types can be introduced. With current implementation, when plugins with new error types are pushed to hub, data pipeline artifacts need to be updated for every new type of error that is introduced. This is because the validation errors are defined in the data pipeline app itself. A better approach would be to modify data pipeline app so that app artifacts do not need to be replaced for every new type of error.

Goals

To fail fast and for better user experience, introduce a new api to collect multiple validation error messages from a stage at configure time
Decouple validation error types from data pipeline app
Instrument plugins to use this api to return multiple error messages for validation endpoint

User Stories

As a CDAP pipeline developer, when I validate a stage, I expect that all the invalid config properties and input/output schema fields are highlighted on CDAP UI with appropriate error message and corrective action.
As a plugin developer, I should be able to capture all the validation errors while configuring the plugin so that all the validation errors can be surfaced on CDAP UI.
As a plugin developer, I should be able to use new validation error types without replacing data pipeline app artifacts.

API Changes for Plugin Validation

Collect Multiple errors from plugins

To collect multiple stage validation errors from the stage, StageConfigurer, MultiInputStageConfigurer and MultiOutputStageConfigurer can be modified as below. Current implementation does not expose stage name to the plugin in configurePipeline method. Stage name will be needed by the plugins to create stage specific errors. For that, stage name will be exposed to plugins through stage configurer as below.

StageConfigurer.java

public interface StageConfigurer {

  ...

/**
 * Get the stage name.
 * 
 * @return stage name
 */
String getStageName();


/**
 * Adds a new validation failure to the configurer.
 *
 * @param failure a validation failure
 */
void addValidationFailure(ValidationFailure failure);

/**
 * Throws validation exception if there are any failures that are added to the configurer through
 * addValidationFailure method.
 *
 * @throws ValidationException if there are any validation failures being carried by the configurer
 */
void throwIfFailure() throws ValidationException;

Decouple plugin error types from data pipeline app

Approach - 1

To carry error information, a new ValidationFailure class is introduced to collect multiple validation failures in stage configurer. This class can be built using a ValidationFailureBuilder which only allows string properties. The builder expose methods to get message, type and properties of a failure. The validation failures are collected using ValidationException. Using this validation exception whenever plugin has an invalid property that is tied to another invalid property, plugin can throw a validation exception with all the errors collected so far. This keep plugin validation code much simpler.

ValidationFailure.java

/**
 * Represents an error condition occurred during validation.
 */
@Beta
public class ValidationFailure {
  // types of the failures
  private static final String STAGE_ERROR = "StageError";
  private static final String INVALID_PROPERTY = "InvalidProperty";
  private static final String PLUGIN_NOT_FOUND = "PluginNotFound";
  private static final String INVALID_INPUT_SCHEMA = "InvalidInputSchema";
  private static final String INVALID_OUTPUT_SCHEMA = "InvalidOutputSchema";

  // represents stage name in the failure. It is a generic property used in all the failures for a given stage
  private static final String STAGE = "stage";

  // represents configuration property in InvalidProperty failure
  private static final String CONFIG_PROPERTY = "configProperty";

  // represents plugin id in PluginNotFound failure
  private static final String PLUGIN_ID = "pluginId";
  // represents plugin type in PluginNotFound failure
  private static final String PLUGIN_TYPE = "pluginType";
  // represents plugin name in PluginNotFound failure
  private static final String PLUGIN_NAME = "pluginName";

  // represents a field in InvalidInputSchema or InvalidOutputSchema failure
  private static final String FIELD = "field";
  // represents input stage in InvalidInputSchema failure
  private static final String INPUT_STAGE = "inputStage";
  // represents output port in InvalidOutputSchema failure
  private static final String OUTPUT_PORT = "outputPort";

  private final String message;
  private final String type;
  private final String correctiveAction;
  private final Map<String, Object> properties;

  private ValidationFailure(String message, String type, @Nullable String correctiveAction,
                            Map<String, Object> properties) {
    this.message = message;
    this.type = type;
    this.correctiveAction = correctiveAction;
    this.properties = properties;
  }

  /**
   * Creates a stage validation failure.
   *
   * @param message validation failure message
   * @param stage stage name
   * @param correctiveAction corrective action
   */
  public static ValidationFailure createStageFailure(String message, String stage, @Nullable String correctiveAction) {
    Builder builder = builder(message, STAGE_ERROR);
    builder.setCorrectiveAction(correctiveAction).addProperty(STAGE, stage);
    return builder.build();
  }

  /**
   * Creates a config property validation failure.
   *
   * @param message validation failure message
   * @param stage stage name
   * @param correctiveAction corrective action
   */
  public static ValidationFailure createConfigPropertyFailure(String message, String stage,
                                                              String property, @Nullable String correctiveAction) {
    Builder builder = builder(message, INVALID_PROPERTY);
    builder.setCorrectiveAction(correctiveAction)
      .addProperty(STAGE, stage).addProperty(CONFIG_PROPERTY, property);
    return builder.build();
  }

  /**
   * Creates a plugin not found validation failure.
   *
   * @param message validation failure message
   * @param stage stage name
   * @param correctiveAction corrective action
   */
  public static ValidationFailure createPluginNotFoundFailure(String message, String stage,
                                                              String pluginId, String pluginName, String pluginType,
                                                              @Nullable String correctiveAction) {
    Builder builder = builder(message, PLUGIN_NOT_FOUND);
    builder.setCorrectiveAction(correctiveAction)
      .addProperty(STAGE, stage).addProperty(PLUGIN_ID, pluginId)
      .addProperty(PLUGIN_TYPE, pluginType)
      .addProperty(PLUGIN_NAME, pluginName);
    return builder.build();
  }

  /**
   * Creates a invalid input schema failure.
   *
   * @param message validation failure message
   * @param stage stage name
   * @param field input schema field
   * @param inputStage optional input stagename. This is applicable to plugins of type {@link Joiner}.
   * @param correctiveAction optional corrective action
   * @return invalid input schema validation failure
   */
  public static ValidationFailure createInputSchemaFailure(String message, String stage, String field,
                                                           @Nullable String inputStage,
                                                           @Nullable String correctiveAction) {
    ...
  }

  /**
   * Creates a invalid output schema failure.
   *
   * @param message validation failure message
   * @param stage stage name
   * @param field output schema field
   * @param outputPort optional output port. This is applicable to plugins of type {@link SplitterTransform}.
   * @param correctiveAction optional corrective action
   * @return invalid output schema validation failure
   */
  public static ValidationFailure createOutputSchemaFailure(String message, String stage, String field,
                                                            @Nullable String outputPort,
                                                            @Nullable String correctiveAction) {
   ....
  }

  /**
   * Returns a builder for creating a {@link ValidationFailure}.
   */
  public static Builder builder(String message, String type) {
    return new Builder(message, type);
  }

  /**
   * A builder to create {@link ValidationFailure} instance.
   */
  public static class Builder {
    private final String message;
    private final String type;
    private String correctiveAction;
    private final Map<String, Object> properties;

    private Builder(String message, String type) {
      this.message = message;
      this.type = type;
      this.properties = new HashMap<>();
    }

    /**
     * Sets corrective action to rectify the failure.
     *
     * @param correctiveAction corrective action
     * @return this builder
     */
    public Builder setCorrectiveAction(String correctiveAction) {
      this.correctiveAction = correctiveAction;
      return this;
    }

    /**
     * Adds a property to the failure.
     *
     * @param property the name of the property
     * @param value the value of the property
     * @return this builder
     */
    public Builder addProperty(String property, String value) {
      this.properties.put(property, value);
      return this;
    }

    /**
     * Creates a new instance of {@link ValidationFailure}.
     *
     * @return instance of {@link ValidationFailure}
     */
    public ValidationFailure build() {
      return new ValidationFailure(message, type, correctiveAction,
                                   Collections.unmodifiableMap(new HashMap<>(properties)));
    }
  }

  /**
   * Returns message of this failure.
   */
  public String getMessage() {
    return message;
  }

  /**
   * Returns type of this failure.
   */
  public String getType() {
    return type;
  }

  /**
   * Returns corrective action for this failure.
   */
  @Nullable
  public String getCorrectiveAction() {
    return correctiveAction;
  }

  /**
   * Returns properties of this failure.
   */
  public Map<String, Object> getProperties() {
    return properties;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    ValidationFailure that = (ValidationFailure) o;
    return message.equals(that.message) && type.equals(that.type) &&
      Objects.equals(correctiveAction, that.correctiveAction) &&
      properties.equals(that.properties);
  }

  @Override
  public int hashCode() {
    return Objects.hash(message, type, correctiveAction, properties);
  }

  @Override
  public String toString() {
    return "ValidationFailure{" +
      "message='" + message + '\'' +
      ", type='" + type + '\'' +
      ", correctiveAction='" + correctiveAction + '\'' +
      ", properties=" + properties +
      '}';
  }
}

ValidationException.java

/**
 * Validation exception that carries multiple validation failures.
 */
@Beta
public class ValidationException extends RuntimeException {
  private List<ValidationFailure> failures;

  public ValidationException(List<ValidationFailure> failures) {
    super(failures.isEmpty() ? "Validation Exception occurred." : failures.iterator().next().getMessage());
    this.failures = failures;
  }

  /**
   * Returns list of failures.
   */
  public List<ValidationFailure> getFailures() {
    return failures;
  }
}

API usage in plugins

@Override
public void configurePipeline(PipelineConfigurer pipelineConfigurer) {
  pipelineConfigurer.createDataset(conf.destinationFileset, FileSet.class);
  StageConfigurer stageConfigurer = pipelineConfigurer.getStageConfigurer();
  // get the name of the stage 
  String stageName = stageConfigurer.getStageName();
  try {
    Pattern.compile(conf.filterRegex);
  } catch (Exception e) {  
    // add validation failure to stage configurer
    stageConfigurer.addValidationFailure(ValidationFailure.createConfigPropertyFailure(e.getMessage(), stageName, "filterRegex", "Make sure the file regex is correct"));
    // plugin can choose to terminate processing here
    stageConfigurer.throwIfFailure();
  }
  if (conf.sourceFileset.equals(conf.destinationFileset)) {
    // add validation failure to stage configurer
    stageConfigurer.addValidationFailure(ValidationFailure.createStageFailure("source and destination filesets must be different", stageName, "Provide different source and destination filesets"));
  }
}

Approach - 2

Validation error represents an error with various causes with different attributes for each cause. For example, when the input schema field type does not match the underlying sink schema, the cause is input field mismatch with attributes such as stage name, field name, suggested type etc. Each error message can be associated to more than one causes. This can happen for plugins such as joiner and splitter where there are multiple input or output schemas from a given stage. For example, when input schemas for joiner are not compatible, the causes will include mismatching fields from input schemas of incoming stages. This means that a validation error can be represented as a list of causes where each cause is a map of cause attribute to its value as shown below.

public interface StageConfigurer {

  ...

/**
 * Add validation failure to this configurer.
 *
 * @param message failure message
 * @param correctiveAction corrective action
 * @return a validation failure
 */
ValidationFailure addFailure(String message, @Nullable String correctiveAction);

/**
 * Throws validation exception if there are any failures that are added to the configurer through
 * {@link #addFailure(String, String)}.
 *
 * @throws ValidationException if there are any validation failures
 */
void throwIfFailure() throws ValidationException;

ValidationException.java

/**
 * Validation exception that carries multiple validation failures.
 */
@Beta
public class ValidationException extends RuntimeException {
  private List<ValidationFailure> failures;

  /**
   * Creates a validation exception with list of failures.
   *
   * @param failures list of validation failures
   */
  public ValidationException(List<ValidationFailure> failures) {
    super(failures.isEmpty() ? "Validation Exception occurred." : failures.iterator().next().getMessage());
    this.failures = failures;
  }

  /**
   * Returns a list of validation failures.
   */
  public List<ValidationFailure> getFailures() {
    return failures;
  }
}

ValidationFailure.java

/**
 * Represents a failure condition occurred during validation.
 */
@Beta
public class ValidationFailure {
  private final String message;
  private final String correctiveAction;
  private final List<Cause> causes;

  /**
   * Creates a validation failure with provided message and corrective action.
   *
   * @param message validation failure message
   * @param correctiveAction corrective action
   */
  public ValidationFailure(String message, String correctiveAction) {
    this.message = message;
    this.correctiveAction = correctiveAction;
    this.causes = new ArrayList<>();
  }

  /**
   * Adds provided cause to this validation failure.
   *
   * @param cause cause of validation failure
   * @return validation failure with provided cause
   */
  public ValidationFailure withCause(Cause cause) {
    causes.add(cause);
    return this;
  }

  /**
   * Adds cause attributes that represents plugin not found failure cause.
   *
   * @param pluginId plugin id
   * @param pluginName plugin name
   * @param pluginType plugin type
   * @return validation failure with plugin not found cause
   */
  public ValidationFailure withPluginNotFoundCause(String pluginId, String pluginName, String pluginType) {
    causes.add(new Cause().with(CauseAttributes.PLUGIN_ID, pluginId).with(CauseAttributes.PLUGIN_NAME, pluginName)
                 .with(CauseAttributes.PLUGIN_TYPE, pluginType));
    return this;
  }

  /**
   * Adds cause attributes that represents plugin configure failure cause.
   *
   * @param pluginConfig plugin config property
   * @return validation failure with invalid plugin config property cause
   */
  public ValidationFailure withPluginConfigCause(String pluginConfig) {
    causes.add(new Cause().with(CauseAttributes.PLUGIN_CONFIG, pluginConfig));
    return this;
  }

  /**
   * Adds cause attributes that represents invalid input schema field failure cause.
   *
   * @param fieldName name of the input schema field
   * @param inputStage stage name
   * @return validation failure with invalid input schema field cause
   */
  public ValidationFailure withInvalidInputSchemaCause(String fieldName, @Nullable String inputStage) {
    causes.add(new Cause().with(CauseAttributes.INPUT_STAGE, inputStage)
                 .with(CauseAttributes.INPUT_SCHEMA_FIELD, fieldName));
    return this;
  }

  /**
   * Adds cause attributes that represents invalid output schema field failure cause.
   *
   * @param fieldName name of the output schema field
   * @param outputPort stage name
   * @return validation failure with invalid output schema field cause
   */
  public ValidationFailure withInvalidOutputSchemaCause(String fieldName, @Nullable String outputPort) {
    causes.add(new Cause().with(CauseAttributes.OUTPUT_PORT, outputPort)
                 .with(CauseAttributes.OUTPUT_SCHEMA_FIELD, fieldName));
    return this;
  }

  /**
   * Returns failure message.
   */
  public String getMessage() {
    return message;
  }

  /**
   * Returns corrective action for this failure.
   */
  @Nullable
  public String getCorrectiveAction() {
    return correctiveAction;
  }

  /**
   * Returns causes that caused this failure.
   */
  public List<Cause> getCauses() {
    return causes;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    ValidationFailure failure = (ValidationFailure) o;
    return message.equals(failure.message) && 
      Objects.equals(correctiveAction, failure.correctiveAction) && causes.equals(failure.causes);
  }

  @Override
  public int hashCode() {
    return Objects.hash(message, correctiveAction, causes);
  }

  /**
   * Represents a cause of a failure.
   */
  @Beta
  public static class Cause {
    private final Map<String, String> attributes;

    /**
     * Creates a failure cause.
     */
    public Cause() {
      this.attributes = new HashMap<>();
    }

    /**
     * Adds attributes to this cause.
     *
     * @param attribute cause attribute name
     * @param value cause attribute value
     * @return this cause
     */
    public Cause with(String attribute, String value) {
      attributes.put(attribute, value);
      return this;
    }

    /**
     * Returns cause attributes.
     */
    public Map<String, String> getAttributes() {
      return attributes;
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      Cause cause = (Cause) o;
      return attributes.equals(cause.attributes);
    }

    @Override
    public int hashCode() {
      return Objects.hash(attributes);
    }
  }
}

All the attributes of a cause can be tracked at central location as below:

CauseAttributes.java

/**
 * Cause attributes constants.
 */
@Beta
public final class CauseAttributes {
  // represents plugin configuration property failure
  public static final String PLUGIN_CONFIG = "pluginConfig";
  // represents id of the plugin
  public static final String PLUGIN_ID = "pluginId";
  // represents type of the plugin
  public static final String PLUGIN_TYPE = "pluginType";
  // represents name of the plugin
  public static final String PLUGIN_NAME = "pluginName";
  // represents input stage
  public static final String INPUT_STAGE = "inputStage";
  // represents field of input stage schema
  public static final String INPUT_SCHEMA_FIELD = "inputField";
  // represents a port of stage output
  public static final String OUTPUT_PORT = "outputPort";
  // represents a field of output port schema
  public static final String OUTPUT_SCHEMA_FIELD = "outputField";
}

API usage in plugins

@Override
public void configurePipeline(PipelineConfigurer pipelineConfigurer) {
  pipelineConfigurer.createDataset(conf.destinationFileset, FileSet.class);
  StageConfigurer stageConfigurer = pipelineConfigurer.getStageConfigurer();
  try {
    Pattern.compile(conf.filterRegex);
  } catch (Exception e) {  
    // add validation error to stage configurer
    stageConfigurer.addFailure(new ValidationFailure(e.getMessage(), "Provide a valid regex for property 'filterRegex'.").withPluginConfigCause("filterRegex"));
  }
  if (conf.sourceFileset.equals(conf.destinationFileset)) {
    // add validation error to stage configurer
    stageConfigurer.addFailure(new ValidationFailure("source and destination filesets must be different", "Provide different fileset for source and destination.")
            .withPluginConfigCause("sourceFileset").withPluginConfigCause("sourceFileset");
    stageConfigurer.addValidationFailure(new InvalidStageFailure("source and destination filesets must be different", stageName));
  }
}

Impact on UI

Type	Description	Scenario	Approach - 1 - Json Response	Approach - 2 - Json Response
StageError	Represents validation error while configuring the stage	If there is any error while connecting to sink while getting actual schema	{ "failures": [ { "type": "StageError", "message": "Could not load jdbc driver class.", "correctiveAction": "Make sure correct driver is available.", "properties": { "stage": "src" } } ] }	{ "errors": [ { "message": "Could not load jdbc driver class.", "correctiveAction" : "Make sure correct driver is available.", "causes": [ { "stage": "src" } ] } ] }
InvalidProperty	Represents invalid configuration property	If config property value contains characters that are not allowed by underlying source or sink	{ "failures": [ { "type": "InvalidProperty", "message": "Property 'millis' should be more than 0.", "correctiveAction": "Make sure 'millis' is greater than 0.", "properties": { "stage": "transform", "configProperty": "millis" } } ] }	{ "errors": [ { "message": "Property 'millis' should be more than 0.", "correctiveAction" : "Make sure 'millis' is greater than 0.", "causes": [ { "stage": "transform", "stageConfig": "millis" } ] } ] }
PluginNotFound	Represents plugin not found error for a stage. This error will be added by the data pipeline app	If the plugin was not found. This error will be thrown from the data pipeline app	{ "failures": [ { "type": "PluginNotFound", "message": "Plugin named 'Mock' of type 'batchsource' not found.", "correctiveAction": "Please make sure the 'Mock' plugin is installed.", "properties": { "stage": "src", "pluginType": "batchsource", "pluginName": "Mock", "pluginId": "Mock" } } ] }	{ "errors": [ { "message": "Plugin named 'Mock' of type 'batchsource' not found.", "correctiveAction" : "Please make sure the 'Mock' plugin is installed.", "causes": [ { "stage": "src", "pluginType": "batchsource", "pluginName": "Mock", "pluginId" : "Mock" } ] } ] }
InvalidInputSchema	Represents invalid schema field in input schema	If the input schemas for joiner plugin is of different types	{ "failures": [ { "type": "InvalidInputSchema", "message": "Invalid schema field 'id'. Different types of join keys found in source1 and source2.", "correctiveAction": "Type of join keys from source1 and source2 must be of same type string", "properties": { "stage": "joiner", "field": "id", "inputStage": "source1" } }, { "type": "InvalidInputSchema", "message": "Invalid schema field 'id'. Different types of join keys found in source1 and source2.", "correctiveAction": "Type of join keys from source1 and source2 must be of same type string", "properties": { "stage": "joiner", "field": "id", "inputStage": "source2" } } ] }	{ "failures": [ { "message": "Different types of join keys found.", "correctiveAction" : "Type of join keys from all the sources must be same.", "causes": [ { "stage": "joiner", "joinKey": "source1.id,source2.id" }, { "stage": "joiner", "inputStage": "source1" "inputField": "id" }, { "stage": "joiner", "inputStage": "source2" "inputField": "id" } ] } ] }
InvalidOutputSchema	Represents invalid schema field in output schema	If the output schema for the plugin is not compatible with underlying sink	{ "failures": [ { "type": "InvalidOutputSchema", "message": "Invalid schema field 'email'.", "correctiveAction": "Schema should be of type 'string' at output port 'port'", "properties": { "stage": "splitter", "field": "email", "outputPort": "port" } } ] }	{ "errors": [ { "message": "Invalid schema field 'email'.", "correctiveAction" : "Schema should be of type 'string' at output port 'port'", "causes": [ { "stage": "splitter", "outputPort": "port", "outputField": "email" } ] } ] }
InvalidFieldInProperty	Represents an invalid field in property list	If the property represents list of fields, the failure should include the property name along with invalid field	{ "failures": [ { "type": "InvalidFieldInProperty", "message": "Unique field 'name' does not exist in the input schema.", "correctiveAction": "Make sure 'name' field is a correct field.", "properties": { "stage": "Deduplicate", "field": "uniqueFields", "configElement": "name" } } ] }	{ "errors": [ { "message": "Unique field 'name' does not exist in the input schema.", "correctiveAction" : "Make sure 'name' field is a correct field.", "causes": [ { "stage": "Deduplicate", "outputPort": "uniqueFields", "outputField": "name" } ] } ] }

Conclusion

There are 2 contracts in this design. Programmatic contract between data pipeline app and plugins and another between data pipeline app and UI. Approach 2 does not introduce concept of failure type. This means that contract with UI will be based on the cause attributes rather than the type. This means that if plugins creates a custom failure and uses any of the UI compatible attributes, the UI can still highlight them. Approach 2 also provides association between causes which represents the failure better in case there are multiple causes causing this failure. Hence, Approach 2 is suggested.

Related Jira

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