Running Tasks

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This topic describes how to run tasks in Cloud Foundry. A task is an app or script whose code is included as part of a deployed app, but runs independently in its own container.

About Tasks

In contrast to a long-running process (LRP), tasks run for a finite amount of time, then stop. Tasks run in their own containers and are designed to use minimal resources. After a task runs, Cloud Foundry destroys the container running the task.

As a single-use object, a task can be checked for its state and for a success or failure message.

Note: Running a task consumes an app instance, and will be billed accordingly.

Use Cases for Tasks

Tasks are used to perform one-off jobs, which include:

  • Migrating a database
  • Sending an email
  • Running a batch job
  • Running a data processing script
  • Processing images
  • Optimizing a search index
  • Uploading data
  • Backing-up data
  • Downloading content

How Tasks Are Run

Tasks are always executed asynchronously, meaning that they run independently from the parent app or other tasks that run on the same app.

The lifecycle of a task is as follows:

  1. A user initiates a task in Cloud Foundry using one of the following mechanisms:

  2. Cloud Foundry creates a container specifically for the task.

  3. Cloud Foundry runs the task on the container using the value passed to the cf run-task command.

  4. Cloud Foundry destroys the container.

The container also inherits environment variables, service bindings, and security groups bound to the app.

Note: You cannot SSH into the container running a task.

Task Logging and Execution History

Any data or messages the task outputs to STDOUT or STDERR is available on the app’s firehose logs. A syslog drain attached to the app receives the task log output.

The task execution history is retained for one month.

Manage Tasks

At the system level, a user with admin-level privileges can use the Cloud Controller v3 API to view all tasks that are running within an org or space. For more information, see List tasks in the Cloud Foundry API documentation.

Additionally, admins can set the default memory and disk usage quotas for tasks on a global level. Initially, tasks use the same memory and disk usage defaults as apps. However, the default memory and disk allocations for tasks can be defined separately from the default app memory and disk allocations.

The default memory and disk allocations are defined using the Default App Memory and Default Disk Quota per App fields. These fields are available in the Application Developer Controls configuration screen of Pivotal Application Service (PAS).

Run a Task on an App

You can use the Cloud Foundry Command Line Interface (cf CLI) to run a task in the context of an app.

Note: To run tasks with the cf CLI, you must install cf CLI v6.23.0 or later. For information about downloading, installing, and uninstalling the cf CLI., see Installing the Cloud Foundry Command Line Interface.

Note: To run a task without starting the app, push the app with cf push -i 0 and then run the task. You can run the app later by scaling up its instance count.

To run a task on an app:

  1. Push your app by running:

    cf push APP-NAME
  2. Run your task on the deployed app by running:

    cf run-task APP-NAME "TASK" --name TASK-NAME

    The following example runs a database migration as a task on the my-app app:

    $ cf run-task my-app "bin/rails db:migrate" --name my-task
    Creating task for app my-app in org jdoe-org / space development as
    Task 1 has been submitted successfully for execution.

    Note: To re-run a task, you must run it as a new task using the above command.

  3. To display the recent logs of the app and all its tasks, run:

    cf logs APP-NAME --recent

    The following example displays the logs of a successful task:

    $ cf logs my-app --recent
    2017-01-03T15:58:06.57-0800 [APP/TASK/my-task/0]OUT Creating container
    2017-01-03T15:58:08.45-0800 [APP/TASK/my-task/0]OUT Successfully created container
    2017-01-03T15:58:13.32-0800 [APP/TASK/my-task/0]OUT D, [2017-01-03T23:58:13.322258 #7] DEBUG -- :    (15.9ms)  CREATE TABLE "schema_migrations" ("version" character varying PRIMARY KEY)
    2017-01-03T15:58:13.33-0800 [APP/TASK/my-task/0]OUT D, [2017-01-03T23:58:13.337723 #7] DEBUG -- :    (11.9ms)  CREATE TABLE "ar_internal_metadata" ("key" character varying PRIMARY KEY, "value" character varying, "created_at" timestamp NOT NULL, "updated_at" timestamp NOT NULL)
    2017-01-03T15:58:13.34-0800 [APP/TASK/my-task/0]OUT D, [2017-01-03T23:58:13.340234 #7] DEBUG -- :    (1.6ms)  SELECT pg_try_advisory_lock(3720865444824511725);
    2017-01-03T15:58:13.35-0800 [APP/TASK/my-task/0]OUT D, [2017-01-03T23:58:13.351853 #7] DEBUG -- :   ActiveRecord::SchemaMigration Load (0.7ms)  SELECT "schema_migrations".* FROM "schema_migrations"
    2017-01-03T15:58:13.35-0800 [APP/TASK/my-task/0]OUT I, [2017-01-03T23:58:13.357294 #7]  INFO -- : Migrating to CreateArticles (20161118225627)
    2017-01-03T15:58:13.35-0800 [APP/TASK/my-task/0]OUT D, [2017-01-03T23:58:13.359565 #7] DEBUG -- :    (0.5ms)  BEGIN
    2017-01-03T15:58:13.35-0800 [APP/TASK/my-task/0]OUT == 20161118225627 CreateArticles: migrating ===================================
    2017-01-03T15:58:13.50-0800 [APP/TASK/my-task/0]OUT Exit status 0
    2017-01-03T15:58:13.56-0800 [APP/TASK/my-task/0]OUT Destroying container
    2017-01-03T15:58:15.65-0800 [APP/TASK/my-task/0]OUT Successfully destroyed container
    The following example displays the logs of a failed task:
    $ cf logs my-app --recent
    2016-12-14T11:09:26.09-0800 [APP/TASK/my-task/0]OUT Creating container
    2016-12-14T11:09:28.43-0800 [APP/TASK/my-task/0]OUT Successfully created container
    2016-12-14T11:09:28.85-0800 [APP/TASK/my-task/0]ERR bash: bin/rails: command not found
    2016-12-14T11:09:28.85-0800 [APP/TASK/my-task/0]OUT Exit status 127
    2016-12-14T11:09:28.89-0800 [APP/TASK/my-task/0]OUT Destroying container
    2016-12-14T11:09:30.50-0800 [APP/TASK/my-task/0]OUT Successfully destroyed container
    If your task name is unique, you can grep the output of the cf logs command for the task name to view task-specific logs.

List Tasks Running on an App

To list the tasks for a given app, run cf tasks APP-NAME. For example:

$ cf tasks my-app
Getting tasks for app my-app in org jdoe-org / space development as

id   name       state       start time                      command
2    339044ef   FAILED      Wed, 23 Nov 2016 21:52:52 UTC   echo foo; sleep 100; echo bar
1    8d0618cf   SUCCEEDED   Wed, 23 Nov 2016 21:37:28 UTC   bin/rails db:migrate

Each task has one of the following states:

State Description
RUNNING The task is currently in progress.
FAILED The task did not complete. This state occurs when a task does not work correctly or a user cancels the task.
SUCCEEDED The task completed successfully.

Cancel a Task

After running a task, you may be able to cancel it before it finishes. To cancel a running task, run cf terminate-task APP-NAME TASK-ID. For example:

$ cf terminate-task my-app 2
Terminating task 2 of app my-app in org jdoe-org / space development as