Composed Task Runner

A task that executes a tasks in a directed graph as specified by a DSL that is passed in via the --graph command line argument.

Overview

The Composed Task Runner parses the graph DSL and for each node in the graph it will execute a restful call against a specified Spring Cloud Data Flow instance to launch the associated task definition. For each task definition that is executed the Composed Task Runner will poll the database to verify that the task completed. Once complete the Composed Task Runner will either continue to the next task in the graph or fail based on how the DSL specified the sequence of tasks should be executed.

Graph DSL

The Graph DSL is comprised of Task Definitions that have been defined within the Spring Cloud Data Flow server referenced by the data-flow-uri (default: http://localhost:9393). These definitions can be placed into a derived graph based on a DSL through the use of sequences, transitions, splits, or a combination therein.

Traversing the graph

Composed Task Runner is built using Spring Batch to execute the directed graph. As such each node in the graph is a Step. As discussed in the overview, each step in the graph will post a request to a Spring Cloud Data Flow Server to execute a task definition. If the task launched by the step fails to complete within the time specified by the maxWaitTime property, a org.springframework.cloud.task.app.composedtaskrunner.support.TimeoutException will be thrown. Once task launched by the step completes, the ComposedTaskRunner will set the ExitStatus of that step based on the following rules:

• If the TaskExecution has an ExitMessage that will be used as the ExitStatus

• If no ExitMessage is present and the ExitCode is set to 0 then the ExitStatus for the step will be COMPLETED.

• If no ExitMessage is present and the ExitCode is set to 1 then the ExitStatus for the step will be FAILED.

If the state of any step in the graph is set to FAILED and is not handled by the DSL the Directed Graph execution will terminate.

Sequences

The Composed Task Runner supports the ability to traverse sequences of task definitions. This is represented by a task definition name followed by the && symbol then the next task definition to be launched. For example if we have tasks AAA, BBB and CCC to be launched in sequence it will look like this:

AAA && BBB && CCC

You can execute the same task multiple times in a sequence. For example:

AAA && AAA && AAA

If an ExitStatus 'FAILED' is returned in a sequence the Composed Task Runner will terminate. For example if AAA && BBB && CCC composed task is executed and BBB fails. Then CCC will not be launched.

Transitions

The Composed Task Runner supports the ability to control what tasks get executed based on the ExitStatus of the previous task. This is done by specifying ExitStatus after the task definition followed by the → operator and the task definition that should be launched based on the result. For example:

AAA 'FAILED' -> BBB 'COMPLETED' -> CCC

Will launch AAA and if AAA fails then BBB will be launched. Else if AAA completes successfully then CCC will launch.

You can also have a sequence that follows a transition. For example:

AAA 'FAILED' -> BBB && CCC && DDD

Will launch AAA and for any ExitStatus that is returned other than 'FAILED' then CCC && DDD will be launched. However if AAA returns 'FAILED' then BBB will be launched, but CCC && DDD will not.

Wildcard

Wildcards are also supported in transitions. For example:

AAA 'FAILED' -> BBB '*'->CCC

In the case above AAA will launch and any ExitStatus other than FAILED will launch CCC.

Splits

Allows a user to execute tasks in parallel. For example:

<AAA || BBB || CCC>

Will launch AAA, BBB and CCC in parallel. When launching splits as a part of a composed task all elements of the split must finish successfully before the next task definition can be launched for example:

<AAA || BBB || CCC> && DDD && EEE

In the case above once AAA, BBB and CCC complete sucessfully then DDD and EEE will be launched in the sequence enumerated above. However if one of the task definitions fails in the split then DDD and EEE will not fire. For example if BBB fails then AAA and CCC will be marked successful and BBB will be marked a failure and DDD and EEE will not be launched.

If any child task within a split returns an ExitMessage other than COMPLETED the split will have an ExitStatus of FAILED. To ignore the ExitMessage of a child task, add the ignoreExitMessage=true for each app that will return an ExitMessage within the split. When using this flag, the ExitStatus of the task will be COMPLETED if the ExitCode of the child task is zero. The split will have an ExitStatus of FAILED if the ExitCode`s is non zero. There are 2 ways to set the `ignoreExitMessage flag:

1. Setting the property for each of the apps that need to have their exitMessage ignored within the split. For example a split like <AAA || BBB> where BBB will return an exitMessage, you would set the ignoreExitMessage property like app.BBB.ignoreExitMessage=true

2. You can also set it for all apps using the composed-task-arguments property, for example: --composed-task-arguments=--ignoreExitMessage=true.

Configuration

See the Configuring Composed Task Runner in the Spring Cloud Data Flow reference guide.