Introduction 

CDAP pipeline is composed of various CDAP plugins. These plugins handle error situations in case of invalid inputs or configurations. While developing CDAP pipeline, pipeline developer can provide invalid plugin configurations. For example, the bigquery sink plugin can have schema which does not match with an underlying bigquery table. In such situations, providing clear error message is helpful to guide user in right direction. Also, when such situation happens, providing all the error messages at once is important for better user experience.

Wrangler provides interactive way for users to apply directives to the data. However, while applying these directives, user may run into error situations. For example, the input json file may be corrupted which can fail parse-as-json directive. In such error situations, user should be provided clear error message so that further actions can be taken.

Goals

There are four goals which needs to be achieved to improve error handling:

• Guideline Have a guideline on how an error message should be formulated that makes it easier for end user to interpret the error situation.

• Improve error messages in Wrangler directives.

• Validate To fail fast, validate fields and plugin schema at the deploy time to fail fast.

• Improve error messages in CDAP plugins.

User Stories

1. As a CDAP pipeline developer, if a pipeline contains plugin configurations which are invalid, I will like it to fail early with appropriate error message.

2. As a Wrangler user, if directive is provided invalid parametersan ETL engineer, if I run into error situation while applying directives, I will like it to fail the operation with see appropriate error message which clearly indicates the error.

Guidelines for Error Messages

An error message is the text used to provide information about error situations. Poorly written error messages can increase support costs and can be a source of frustration for users. Well-written error messages are very important for better user experience. Below is the guideline on writing better error messages. 

1. Error messages should be contextual.

Contextual error messages provide specific information particular to error situation. Error messages without any context are very hard to interpret by users. Contextual information may include information such as why the error happened, what is the error value, what is the expected value, how user can fix the error etc.

For example, if there is a mismatch in data type of a field, providing more contextual information to user in error message would help user understand the problem and fix it if needed. 

Error Message:
Data type mismatch for field 'X'. 

Better Error Message:
Field 'X' is expected to be of data type 'int'. However, provided data type is 'string'.

2. Do not include implementation details in user facing error messages.

Exposing implementation details to end users can be confusing and users may not be able to take any action to solve error situation. Thats why user facing error messages should not include implementation details. Below are some of the cases where we can avoid exposing implementation details:

• Avoid using class hashes in error messages. For example:

  No Format
  Error Message: co.cask.directives.language.SetCharset@781ecbac : Invalid type 'java.lang.String' of column 'body'. Should be of type String. Better Error Message: Error executing 'set-charset' directive: The 'body' column was expected to be a byte array or ByteBuffer, but is of type 'String'.

• Avoid using exception class names in user facing error messages. For example:

  No Format
  Error Message: java.lang.IllegalArgumentException: Database driver 'cloudsql-postgresql' not found. Better Error Message: Database driver 'cloudsql-postgresql' not found. Please make sure correct database driver is deployed.

• Avoid using technical implementation details in user facing error messages. For example:

  No Format
  Error Message: Failed to configure pipeline: valueOf operation on abc failed. Better Error Message: Failed to configure pipeline: Expected type of field 'X' is either int/double but found 'abc'.

3. Error message should provide direction to user if action is needed from user.

An error message has 3 parts, problem identification, cause details if helpful, and a solution if possible. Whenever error situation occurs, users would like to fix it immediately. The error message should have enough information to guide the user in right direction.

4. Provide complete concise error message to user and avoid ambiguity.

An error message should be a complete sentence which provides clear message. User should be able to understand the problem by reading the error message. For example:

Error Message:
io.cdap.directives.transformation.Decode@c2e00f5 : Failed to decode hex value.

Better Error Message:
Error while decoding field 'X' as hex value. Please make sure the provided field is encoded as hex.

5. Always prefer error message specific to the error situation instead of generic error messages

Whenever possible, use specific error message instead of generic error message. For example:

Error Message:
Failed to decode hex value.

Better Error Message:
Error while decoding field 'X' as hex value. Please make sure the provided field is encoded as hex.

Scope

Dataprep

• Improve error messages in all Directives
  • Remove usages of object hashes in the error messages
  • Update error messages to be more contextual
  • In Http Handlers, add cause to the thrown exception for debugging so that the cause is not lost

Plugins

• Improve error messages in plugins (core-plugins and google-cloud plugins to start with)
• Fail Fast
  • Validation should include multiple errors per schema field
  • Validation should include multiple errors per stage config property

Platform

• Improve user facing error messages from HttpHandlers
• When a mapreduce job/pipeline fails actual cause of error are logged under WARN level instead of ERROR log level.

Bug Fixes 

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-14378

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15499

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15507

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15040

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15593

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-14797

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15563

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15560

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-11767

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15426

• Jira Legacy
  server Cask Community Issue Tracker columns key,summary,type,created,updated,due,assignee,reporter,priority,status,resolution serverId 45b48dee-c8d6-34f0-9990-e6367dc2fe4b key CDAP-15581

Impact on UI

Approach

Approach #1

Approach #2

API changes

New Programmatic APIs

New Java APIs introduced (both user facing and internal)

Deprecated Programmatic APIs

New REST APIs

Deprecated REST API

CLI Impact or Changes

• Impact #1

• Impact #2

• Impact #3

UI Impact or Changes

• Impact #1

• Impact #2

• Impact #3

Security Impact 

What's the impact on Authorization and how does the design take care of this aspect

Impact on Infrastructure Outages 

System behavior (if applicable - document impact on downstream [ YARN, HBase etc ] component failures) and how does the design take care of these aspect

Test Scenarios

Releases

Release 6.1.0

Related Work

• Work #1

• Work #2

• Work #3

Future work