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* play, block, task: New attribute forks With this it is possible to limit the number of concurrent task runs. forks can now be used in play, block and task. If forks is set in different levels in the chain, then the smallest value will be used for the task. The attribute has been added to the Base class as a list to easily provide all the values that have been set in the different levels of the chain. A warning has been added because of the conflict with run_once. forks will be ignored in this case. The forks limitation in StrategyBase._queue_task is not used for the free strategy. Signed-off-by: Thomas Woerner <twoerner@redhat.com> * Handle forks in free strategy The forks attribute for the free strategy is handled in run in the free StrategyModule. This is dony by counting the amount of tasks where the uuid is the same as the current task, that should be queued next. If this amount is bigger or equal to the forks attribute from the chain (task, block, play), then it will be skipped to the next host. Like it is also done with blocked_hosts. Signed-off-by: Thomas Woerner <twoerner@redhat.com> * Test cases for forks with linear and free strategy With ansible_python_interpreter defined in inventory file using ansible_playbook_python. Signed-off-by: Thomas Woerner <twoerner@redhat.com> * Changing forks keyword to throttle and adding some more docs
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Controlling playbook execution: strategies and more
By default, Ansible runs each task on all hosts affected by a play
before starting the next task on any host, using 5 forks. If you want to
change this default behavior, you can use a different strategy plugin,
change the number of forks, or apply one of several play-level keywords
like serial.
Selecting a strategy
The default behavior described above is the linear strategy<linear_strategy>. Ansible offers
other strategies, including the debug strategy<debug_strategy> (see also playbook_debugger) and the
free strategy<free_strategy>, which allows each
host to run until the end of the play as fast as it can:
- hosts: all
strategy: free
tasks:
...You can select a different strategy for each play as shown above, or
set your preferred strategy globally in ansible.cfg, under
the defaults stanza:
[defaults]
strategy = freeAll strategies are implemented as strategy plugins<strategy_plugins>. Please
review the documentation for each strategy plugin for details on how it
works.
Setting the number of forks
If you have the processing power available and want to use more
forks, you can set the number in ansible.cfg:
[defaults]
forks = 30or pass it on the command line: ansible-playbook -f 30 my_playbook.yml.
Using keywords to control execution
Several play-level keyword<playbook_keywords> also affect play
execution. The most common one is serial, which sets a
number, a percentage, or a list of numbers of hosts you want to manage
at a time. Setting serial with any strategy directs Ansible
to 'batch' the hosts, completing the play on the specified number or
percentage of hosts before starting the next 'batch'. This is especially
useful for rolling updates<rolling_update_batch_size>.
The second keyword to affect execution is throttle,
which can also be used at the block and task level. This keyword limits
the number of workers up to the maximum set via the forks setting or
serial. This can be useful in restricting tasks that may be
CPU-intensive or interact with a rate-limiting API:
tasks:
- command: /path/to/cpu_intensive_command
throttle: 1Other keywords that affect play execution include
ignore_errors, ignore_unreachable, and
any_errors_fatal. Please note that these keywords are not
strategies. They are play-level directives or options.
about_playbooks-
An introduction to playbooks
playbooks_reuse_roles-
Playbook organization by roles
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