iwf

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iWF project - main & server repo

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iWF will make you a 10x developer!

iWF is an all-in-one platform for developing long-running business processes. It offers a convenient abstraction layer for utilizing databases, ElasticSearch, message queues, durable timers, and more, with a clean, simple, and user-friendly interface.

iWF is a versatile WorkflowAsCode engine that is both simple and powerful. By utilizing Cadence/Temporal as an interpreter on the backend, iWF preserves all the capabilities of Cadence/Temporal, while maintaining the same level of scalability and reliability.

Related projects:

Table of contents

Community & Help

What is iWF

Architecture

An iWF application is composed of several iWF workflow workers. These workers host two REST APIs for WorkflowState start and decide. The application utilizes the iWF SDKs to communicate with an iWF server and perform actions on workflow executions, such as starting, stopping, signaling, and retrieving results

The iWF server provides the APIs, which are also RESTful, as a iWF API service. Internally, this API service communicates with the Cadence/Temporal service as its backend.

In addition to hosting the iWF API service, the iWF server includes Cadence/Temporal workers that host an interpreter workflow. This interpreter workflow interprets any iWF workflows into the Cadence/Temporal workflow. It then invokes the two application worker APIs (WorkflowState start and decide) through Cadence/Temporal activities. As a result, all REST API requests and responses are recorded as history events, which can be useful for debugging and troubleshooting purposes. This means that there's no need to replay the application workflow code.

architecture diagram

Basic Concepts

Workflow and WorkflowState definition

A long-running process is called Workflow.

iWF enables the building of long-running applications by implementing the Workflow interface in either Golang or Java. An implementation of the interface is referred to as a WorkflowDefinition.

A WorkflowDefinition consists of multiple WorkflowStates, which can be implemented using either the Java WorkflowState interface or Golang WorkflowState interface. A WorkflowState is implemented using two APIs: the start API and the decide API:

  • The start API is invoked as soon as a WorkflowState is started. It returns a set of Commands to the server, and once these commands are completed, the decide API is triggered. The number of commands can range from zero to multiple.
  • The decide API determines the next set of states to be executed. The next states can range from zero to multiple.

The same WorkflowState can be re-executed as different stateExecutions.

workflow diagram example

Workflow execution and WorkflowState execution

An application can initiate a workflow instance for any WorkflowDefinition using a workflowId. The instance of a workflow is referred to as a WorkflowExecution. The iWF server returns a runId, which is a universally unique identifier (UUID), as the identifier for the WorkflowExecution. The runId is guaranteed to be globally unique.

⚠ Note:

Depending on the context, the term "workflow" may refer to a WorkflowExecution (most commonly), a WorkflowDefinition, or both.

For a running WorkflowExecution, there must be at least one WorkflowState being executed, and if there are none, the WorkflowExecution will be marked as completed. An instance of a WorkflowState's execution is referred to as a StateExecution and is identified by a StateExecutionId. The StateExecutionId is formatted as <StateId>-<Number>, where the StateId is defined by the WorkflowState definition and the Number represents the number of times the StateId has been started. The StateExecutionId is unique only within the context of a specific WorkflowExecution.

Uniqueness and Reuse of WorkflowId: At any given time, there can be only one WorkflowExecution running for a specific workflowId. A new WorkflowExecution can be initiated using the same workflowId by setting the appropriate IdReusePolicy in WorkflowOptions.

  • ALLOW_IF_NO_RUNNING
    • Allow starting workflow if there is no execution running with the workflowId
    • This is the default policy if not specified in WorkflowOptions
    • Equivalent to ALLOW_DUPLICATE in Cadence/Temporal IdReusePolicy
  • ALLOW_IF_PREVIOUS_EXISTS_ABNORMALLY
    • Allow starting workflow if a previous Workflow Execution with the same Workflow Id does not have a Completed status. Use this policy when there is a need to re-execute a Failed, Timed Out, Terminated or Cancelled workflow execution.
    • Equivalent to ALLOW_DUPLICATE_FAILED_ONLY in Cadence/Temporal IdReusePolicy
  • DISALLOW_REUSE
    • Not allow to start a new workflow execution with the same workflowId.
    • Equivalent to REJECT_DUPLICATE in Cadence/Temporal IdReusePolicy
  • TERMINATE_IF_RUNNING
    • Always allow starting workflow no matter what -- iWF server will terminate the current running one if it exists.
Commands

The following are the three types of commands:

  • SignalCommand: will wait for a signal to be published to the workflow signal channel. External application can use SignalWorkflow API to signal a workflow.
  • TimerCommand: will wait for a durable timer to fire.
  • InterStateChannelCommand: will wait for a value to be published from another state in the same workflow execution

The start API can return multiple commands and choose a different DeciderTriggerType to trigger the decide API. The available options for the DeciderTriggerType are:

  • AllCommandCompleted: This option waits for all commands to be completed.

  • AnyCommandCompleted: This option waits for any of the commands to be completed.

  • AnyCommandCombinationCompleted: This option waits for any combination of the commands in a specified list to be completed.

Persistence

iWF offers a highly simplified persistence abstraction, which eliminates the need for developers to interact with any database systems to register or maintain schemas. The only schema that needs to be defined is in the workflow code.

  • DataObject
    • are used for sharing data values across the workflow.
    • can be retrieved by external application using GetDataObjects API
    • can be viewed in Cadence/Temporal WebUI in QueryHandler tab
  • SearchAttribute:
    • are used for sharing data values across the workflow similarly to DataObjects
    • can be retrieved by external application using GetSearchAttributes API
    • are used for searching for workflows by external application using SearchWorkflow API
    • are used for searching for workflows in Cadence/Temporal WebUI in Advanced tab
    • any search attribute type must be registered in Cadence/Temporal server before using for searching because it is backed up ElasticSearch
    • See Temporal doc and Cadence doc to understand more about SearchAttribute
  • StateLocals
    • are used for passing data values from the start API to the decide API within the same StateExecution, thereby reducing the need to use DataObjects
  • RecordEvents
    • are used to record events within the state execution and are useful for debugging using the Workflow history. They can be used to record the input and output of dependency RPC calls, for example

Logically, each workflow type will have a persistence schema like below:

+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
| workflowId  | runId | dataObject key1 | dataObject key2 | searchAttribute key1 | searchAttribute key2 | ... |
+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
| your-wf-id1 | uuid1 | valu1           | value2          | keyword-value1       | 123(integer)         | ... |
+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
| your-wf-id1 | uuid2 | value3          | value4          | keyword-value2       | 456(integer)         | ... |
+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
| your-wf-id2 | uuid3 | value5          | value5          | keyword-value3       | 789(integer)         | ... |
+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
| ...         | ...   | ...             | ...             | ...                  | ...                  | ... |
+-------------+-------+-----------------+-----------------+----------------------+----------------------+-----+
Communication

iWF has two primary communication mechanisms:

  • SignalChannel: is used for receiving input from external sources asynchronously. It is employed with the SignalCommand.
  • InterStateChannel: is used for communication between state executions. It is employed with the InterStateChannelCommand.
iWF workflow design diagram

When creating an iWF workflow, utilizing state diagrams similar to this template can be beneficial for visualizing the process.

state diagram template

For example, the subscription workflow diagram:

subscription state diagram

Client APIs

Client APIs are hosted by iWF server for user workflow application to interact with their workflow executions.

  • Start workflow: start a new workflow execution
  • Stop workflow: stop a workflow execution
  • Signal workflow: send a signal to a workflow execution
  • Search workflow: search for workflows using a query language like SQL with search attributes
  • Get workflow: get basic information about a workflow like status and results(if completed or waiting for completed)
  • Get workflow data objects: get the dataObjects of a workflow execution
  • Get workflow search attributes: get the search attributes of a workflow execution
  • Reset workflow: reset a workflow to previous states
  • Skip timer: skip a timer of a workflow (usually for testing or operation)

Why iWF

If you are familiar with Cadence/Temporal/AWS SWF/Azure Durable Functions

Check iWF vs Cadence/Temporal for comparison with Cadence/Temporal.

The article should still apply to AWS SWF and Azure Durable Functions:

  • AWS SWF is the predecessor of Cadence/Temporal and shares the same API, but its capabilities and features are more limited when compared.
    • For a comparison between SWF and Cadence, refer to this post
  • Azure Durable Functions shared the same programming model(replay based workflow execution engine) but also with limited features compared to Cadence/Temporal.
    • Additionally, it is recommended to read this article about the pitfall about the programming model

If you are not

Check out this article to understand difference between iWF and other workflow engines.

TL;DR:

  • WorkflowAsCode for highly flexible/customizable business logic, highly testable and easy to maintain
  • Parallel execution of multiple threads of business
  • Persistence storage for intermediate states stored as "dataObjects"
  • Persistence searchable attributes that can be used for flexible searching, even full text searching, backed by ElasticSearch
  • Receiving data from external system by Signal
  • Durable timer, and cron job scheduling
  • Reset workflow to let you recover the workflows from bad states easily
  • Troubleshooting/debugging is easy
  • Scalability/reliability
  • ...

How to run this server

Using docker image & docker-compose

Checkout this repo, go to the docker-compose folder and run it:

cd docker-compose && docker-compose up

This by default will run Temporal server with it. And it will also register a default Temporal namespace and required search attributes by iWF. Link to the Temporal WebUI: http://localhost:8233/namespaces/default/workflows

By default, iWF server is serving port 8801, server URL is http://localhost:8801/ )

NOTE:

Use docker pull iworkflowio/iwf-server:latest to update the latest image.Or update the docker-compose file to specify the version tag.

How to build & run locally

  • Run make bins to build the binary iwf-server
  • Make sure you have registered the system search attributes required by iWF server:
    • Keyword: IwfWorkflowType
    • Int: IwfGlobalWorkflowVersion
    • Keyword: IwfExecutingStateIds
    • See Contribution for more detailed commands.
    • For Cadence without advancedVisibility enabled, set disableSystemSearchAttributes to true
  • Then run ./iwf-server start to run the service . This defaults to serve workflows APIs with Temporal interpreter implementation. It requires to have local Temporal setup. See Run with local Temporal.
  • Alternatively, run ./iwf-server --config config/development_cadence.yaml start to run with local Cadence. See below instructions for setting up local Cadence.

How to use in production

You can customize the docker image, or just use the api and interpreter that are exposed as the api service and workflow service.

  • Also make sure you have registered the system search attributes required by iWF server:
    • Keyword: IwfWorkflowType
    • Int: IwfGlobalWorkflowVersion
    • Keyword: IwfExecutingStateIds
    • See Contribution for more detailed commands.
    • For Cadence without advancedVisibility enabled, set disableSystemSearchAttributes to true

For more info, contact qlong.seattle@gmail.com

Monitoring and Operations

iWF server

There are two components for iWF server: API service and interpreter worker service.

For API service, set up monitors/dashboards:

  • API availability
  • API latency

The interpreter worker service is just a standard Cadence/Temporal workflow application. Follow the developer guides:

iWF application

As you may realize, iWF application is a typical REST microservice. You just need the standard ways to operate it.

Usually, you need to set up monitors/dashboards:

  • API availability
  • API latency

Troubleshooting

When something goes wrong in your applications, here are the tips:

  • Use query handlers like (DumpAllInternal or GetCurrentTimerInfos) in Cadence/Temporal WebUI to quickly understand the current status of the workflows.
    • DumpAllInternal will return all the internal status or the pending states
    • GetCurrentTimerInfos will return all the timers of the pending states
  • Let your worker service return error stacktrace as the response body to iWF server. E.g. like this example of Spring Boot using ExceptionHandler.
  • If you return the full stacktrace in response body, the pending activity view will show it to you! Then use Cadence/Temporal WebUI to debug your application.
  • All the input/output to your workflow are stored in the activity input/output of history event. The input is in ActivityTaskScheduledEvent, output is in ActivityTaskCompletedEvent or in pending activity view if having errors.

Operation

In additional of using Cadence/Temporal CLI, you can just use some HTTP script like this to operate on workflows to:

  • Start a workflow
  • Stop a workflow
  • Reset a workflow
  • Skip a timer
  • etc, any APIs supported by the iWF server API schema

How to migrate from Cadence/Temporal

Check this wiki for how to migrate from Cadence/Temporal.

Development Plan

1.0
  • Start workflow API
  • Executing start/decide APIs and completing workflow
  • Parallel execution of multiple states
  • Timer command
  • Signal command
  • SearchAttributeRW
  • DataObjectRW
  • StateLocal
  • Signal workflow API
  • Get DataObjects/SearchAttributes API
  • Get workflow info API
  • Search workflow API
  • Stop workflow API
  • Reset workflow API
  • Command type(s) for inter-state communications (e.g. internal channel)
  • AnyCommandCompleted Decider trigger type
  • More workflow start options: IdReusePolicy, cron schedule, retry
  • StateOption: Start/Decide API timeout and retry policy
  • Reset workflow by stateId or stateExecutionId
  • StateOption.PersistenceLoadingPolicy: LOAD_PARTIAL_WITHOUT_LOCKING
1.1
  • More Search attribute types: Datetime, double, bool, keyword array, text
  • More workflow start options: initial search attributes
1.2
  • Skip timer API for testing/operation
  • Decider trigger type: any command combination
1.3
  • Support failing workflow with results
  • Support differentiate different uncompleted workflow closed status for GetWorkflow
Future
  • Auto continueAsNew(WIP)
  • WaitForMoreResults in StateDecision
  • LongRunningActivityCommand
  • More Decider trigger type
  • Failing workflow details
  • StateOption.PersistenceLoadingPolicy: LOAD_ALL_WITH_EXCLUSIVE_LOCK and LOAD_PARTIAL_WITH_EXCLUSIVE_LOCK

Some history

AWS introduced SWF in 2012, but later switched to Step Functions in 2016 because they found it difficult to support. Cadence and Temporal picked up where SWF left off and extend with more features and more robust, but keeping the same programming models. Programming with SWF/Cadence/Temporal is challenging because it exposes too many internal details. iWF was created to offer the same level of power as Cadence and Temporal, but with a clean and simple API that hides all the underlying complexity.

For more information, please see the document.

history diagram

Posts & Articles

Directories

Path Synopsis
cmd
server
server/iwf
gen
iwfidl
workflow/any_command_close
workflow/any_command_combination
workflow/any_timer_signal
workflow/basic
workflow/common
workflow/interstate
workflow/parallel
workflow/persistence
workflow/signal
workflow/timer
workflow/wf_force_fail
workflow/wf_state_api_fail
workflow/wf_state_api_timeout
api
api/cadence
api/temporal
common/config
common/errors
common/log
common/log/loggerimpl
common/log/tag
common/mapper
common/ptr
common/retry
common/timeparser
interpreter
interpreter/cadence
interpreter/temporal

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