Running operation on another host?

[dvdkon]

Hi, we're (together with @yagarea) looking at rewriting our home server's setup scripts from Ansible to pyinfra. One thing we ran into is that we didn't find any way to run operations on another host (a replacement for Ansible's delegate_to).

Our main usecase for this is a script that creates a new Incus container. It needs to run commands on the host, to create the container and change its config, then in the container itself, to set up networking and install basic packages.

Is there some straightforward way to do this I just missed, or is there some reason this can't be don with pyinfra?

[Dexmachi]

This can probably be done with pure python

idk how, but this would be great for Pyinfra scalling

[maisim]

Is there some straightforward way to do this I just missed, or is there some reason this can't be don with pyinfra?

Hi, what about something like this ?

# inventory.fr

incus_servers = [
    ("my-incus-host", {}),
]

containers = ['("c1", {})]

# deploy.py

from pyinfra import host
from pyinfra.operations import ...

# Use Hostname

if host.name == "my-incus-host"
  incus.instance(
      name="Create container c1",
      instance="c1
  )

if "containers" in  host.groups:
    apt.packages(
        name="Install base packages",
        packages=["vim", "curl"]
    )

[maisim]

I think I finally understood the key point about delegate_to, and why you couldn’t find an equivalent in pyinfra.

In Ansible, a task still belongs to the current host (loop/context), but is executed on another host via delegate_to. So you get this mix of “who the task is for” vs “where it runs”.

In pyinfra, there’s no such split: an operation always runs on the host it targets. If you want something to happen on another host, you just target that host directly. There’s no concept of “delegating” mid-task.

So rather than trying to replicate delegate_to, the intended approach in pyinfra is to structure your deploy so that each operation is applied to the right hosts explicitly (and split stages if needed).

---

Key difference

Concept	Ansible (delegate_to)	pyinfra
Model	task-centric	host-centric
Execution context	stays on current host	tied to target host
Where it runs	can be delegated	always runs on target
Implicit loop	yes	no
Mental model	"run for A on B"	"run on B"

[dvdkon]

Thanks for your insight. The idea with conditionally executing operations based on hostname looks like a good workaround, and I didn't think of that. I'd rather not use it forever, though.

I'll probably end up writing a wrapper over pyinfra using its Python API, since I was already looking into doing that to better support our workflow (one script per container, and minimal horizontal scaling). At that level, "delegating" should hopefully be straightforward.