Software Heritage - Job scheduler¶
Task manager for asynchronous/delayed tasks, used for both recurrent (e.g., listing a forge, loading new stuff from a Git repository) and one-off activities (e.g., loading a specific version of a source package).
This module provides a scheduler service for the Software Heritage platform. It allows to define tasks with a number of properties. In this documentation, we will call these swh-tasks to prevent confusion. These swh-tasks are stored in a database, and a HTTP-based RPC service is provided to create or find existing swh-task declarations.
The execution model for these swh-tasks is using Celery. Thus, each swh-task type defined in the database must have a (series of) celery worker capable of executing such a swh-task.
Then a number of services are also provided to manage the scheduling of these swh-tasks as Celery tasks.
The scheduler-runner service is a daemon that regularly looks for swh-tasks in the database that should be scheduled. For each of the selected swh-task, a Celery task is instantiated.
The scheduler-listener service is a daemon that listen to the Celery event bus and maintain scheduled swh-tasks workflow status.
SWH Task Model¶
Each swh-task-type is the declaration of a type of swh-task. Each swh-task-type have the following fields:
type: Name of the swh-task type; can be anything but must be unique,
description: Human-readable task description
backend_name: Name of the task in the job-running backend,
default_interval: Default interval for newly scheduled tasks,
min_interval: Minimum interval between two runs of a task,
max_interval: Maximum interval between two runs of a task,
backoff_factor: Adjustment factor for the backoff between two task runs,
max_queue_length: Maximum length of the queue for this type of tasks,
num_retries: Default number of retries on transient failures,
retry_delay: Retry delay for the task,
Existing swh-task-types can be listed using the swh scheduler command line tool:
$ swh scheduler task-type list Known task types: check-deposit: Pre-checking deposit step before loading into swh archive index-fossology-license: Fossology license indexer task load-git: Update an origin of type git load-hg: Update an origin of type mercurial
You can see the details of a swh-task-type:
$ swh scheduler task-type list -v -t load-git Known task types: load-git: swh.loader.git.tasks.UpdateGitRepository Update an origin of type git interval: 64 days, 0:00:00 [12:00:00, 64 days, 0:00:00] backoff_factor: 2.0 max_queue_length: 5000 num_retries: None retry_delay: None
An swh-task is an ‘instance’ of such a swh-task-type, and consists in:
arguments: Arguments passed to the underlying job scheduler,
next_run: Next run of this task should be run on or after that time,
- current_interval: Interval between two runs of this task, taking into
account the backoff factor,
policy: Whether the task is “one-shot” or “recurring”,
- retries_left: Number of “short delay” retries of the task in case of
priority: Priority of the task,
id: Internal task identifier,
type: References task_type table,
- status: Task status ( among “next_run_not_scheduled”, “next_run_scheduled”,
So a swh-task consist basically in:
a set of parameters defining how the scheduling of the swh-task is handled,
a set of parameters to specify the retry policy in case of transient failure upon execution,
a set of parameters that defines the job to be done (bakend_name + arguments).
You can list pending swh-tasks (tasks that are to be scheduled ASAP):
$ swh scheduler task list-pending load-git --limit 2 Found 1 load-git tasks Task 9052257 Next run: 15 days ago (2019-06-25 10:35:10+00:00) Interval: 2 days, 0:00:00 Type: load-git Policy: recurring Args: 'https://github.com/turtl/mobile' Keyword args:
Looking for existing swh-task can be done via the command line tool:
$ swh scheduler task list -t load-hg --limit 2 Found 2 tasks Task 168802702 Next run: in 4 hours (2019-07-10 17:56:48+00:00) Interval: 1 day, 0:00:00 Type: load-hg Policy: recurring Status: next_run_not_scheduled Priority: Args: 'https://bitbucket.org/kepung/pypy' Keyword args: Task 169800445 Next run: in a month (2019-08-10 17:54:24+00:00) Interval: 32 days, 0:00:00 Type: load-hg Policy: recurring Status: next_run_not_scheduled Priority: Args: 'https://bitbucket.org/lunixbochs/pypy-1' Keyword args:
Writing a new worker for a new swh-task-type¶
When you want to add a new swh-task-type, you need a celery worker backend capable of executing this new task-type instances.
Celery workers for swh-scheduler based tasks should be started using the Celery app in swh.scheduler.celery_config. This later, among other things, provides a loading mechanism for task types based on pkg_resources declared plugins under the [swh.workers] entry point.
TODO: add a fully working example of a dumb task.
- Command-line interface
- Software Heritage Scheduler Simulator
- swh.scheduler package
- swh.scheduler.api package
- swh.scheduler.celery_backend package
- swh.scheduler.cli package
- swh.scheduler.simulator package
- swh.scheduler.backend module
- swh.scheduler.backend_es module
- swh.scheduler.cli_utils module
- swh.scheduler.elasticsearch_memory module
- swh.scheduler.exc module
- swh.scheduler.interface module
- swh.scheduler.journal_client module
- swh.scheduler.model module
- swh.scheduler.pytest_plugin module
- swh.scheduler.task module
- swh.scheduler.utils module