No concurrency when using delegate_to

[bmerry]

Background: we have a playbook that loads a new BIOS on a server, using a command-line tool that runs on the controller and remotely uploads the BIOS. This takes about 20-30 minutes. Since it runs on the controller, we use delegate_to: localhost.

With the standard ansible strategy, this works fine, but when using mitogen, the executions are serialised, and it takes much longer to update a fleet.

I've put a minimal example below.

• Which version of Ansible are you running? ansible-10.6.0, ansible-core-2.17.6

• Is your version of Ansible patched in any way? No, installed directly from pip in a fresh virtualenv.

• Are you running with any custom modules, or module_utils loaded? No

• Have you tried the latest master version from Git? No, using 0.3.18

• Do you have some idea of what the underlying problem may be? No

• Mention your host and target OS and versions: Ubuntu 24.04 on host (targets are not connected to)

• Mention your host and target Python versions: Python 3.12.3

To reproduce

ansible.cfg:

[defaults]
inventory = inventory
strategy_plugins = <YOUR PATH HERE>

[ssh_connection]
pipelining = True

play.yml:

- hosts: all
  gather_facts: false
  tasks:
    - name: sleep on localhost
      delegate_to: localhost
      ansible.builtin.command: "sleep 20"

inventory:

host1
host2

Running ansible-playbook play.yml takes ±20s as the sleeps run in parallel.

Running ANSIBLE_STRATEGY=mitogen_linear takes ±40s as the sleeps run serially.