Podman driver silently ignores `memory`, `memory_swap`, and `pids_limit` platform fields

[hackaholic]

Prerequisites

• This was not already reported in the past (duplicate check)
• It does reproduce it with code from main branch (latest unreleased version)
• I include a minimal example for reproducing the bug
• The bug is not trivial, as for those a direct pull-request is preferred
• Running pip check does not report any conflicts
• I was able to reproduce the issue on a different machine
• The issue is not specific to any driver other than 'default' one

Environment

molecule 26.6.0
molecule-plugins 25.8.12
containers.podman collection 1.16.2
podman version 4.6.2
Operating system: Ubuntu 22.04.5 LTS (Jammy Jellyfish)
Kernel: Linux 5.19.17-051917-generic
Architecture: x86_64
Python: 3.10.12
rootless: true
cgroup version: v2
cgroup filesystem: cgroup2fs
cgroup manager: systemd

What happened

The bundled Molecule Podman create playbook silently ignores the platform fields
memory, memory_swap, and pids_limit. The same platform's ulimits field is
forwarded correctly.

Reproducing example

## Summary

The bundled Molecule Podman create playbook silently ignores the platform fields
`memory`, `memory_swap`, and `pids_limit`. The same platform's `ulimits` field is
forwarded correctly.

The underlying `containers.podman.podman_container` module supports all four
parameters, and passing the missing limits through the Podman driver's
`extra_opts` produces the expected container configuration.

The bundled Docker create playbook already forwards `memory` and `memory_swap`,
making equivalent Molecule platform configuration inconsistent between Docker
and Podman.

## Minimal reproduction


---
driver:
  name: podman

platforms:
  - name: molecule-podman-limits-repro
    image: docker.io/geerlingguy/docker-ubuntu2204-ansible:latest
    pre_build_image: true
    command: sleep infinity
    memory: 268435456
    memory_swap: 536870912
    pids_limit: 1234
    ulimits:
      - nofile=4096:4096
      - nproc=8192:8192

provisioner:
  name: ansible

scenario:
  create_sequence:
    - create
  destroy_sequence:
    - destroy


Run:


molecule create -s default
podman inspect molecule-podman-limits-repro \
  --format 'Memory={{.HostConfig.Memory}} MemorySwap={{.HostConfig.MemorySwap}} PidsLimit={{.HostConfig.PidsLimit}} Ulimits={{json .HostConfig.Ulimits}}'


## Actual result


Memory=0
MemorySwap=0
PidsLimit=16384
Ulimits=[
  {"Name":"RLIMIT_NOFILE","Soft":4096,"Hard":4096},
  {"Name":"RLIMIT_NPROC","Soft":8192,"Hard":8192}
]


`PidsLimit=16384` is the user's Podman `containers.conf` default. The requested
value `1234` was not applied. Memory and swap are unlimited (`0`). Both ulimits
were applied correctly.

## Source evidence

Installed bundled Podman playbook:


molecule_plugins/podman/playbooks/create.yml


The `containers.podman.podman_container` task maps:


ulimits: "{{ item.ulimits | default(omit) }}"


It has no mappings for:


memory: "{{ item.memory | default(omit) }}"
memory_swap: "{{ item.memory_swap | default(omit) }}"
pids_limit: "{{ item.pids_limit | default(omit) }}"


By comparison, the installed bundled Docker playbook maps at least:


memory: "{{ item.memory | default(omit) }}"
memory_swap: "{{ item.memory_swap | default(omit) }}"
ulimits: "{{ item.ulimits | default(omit) }}"


The underlying `containers.podman.podman_container` module supports `memory`,
`memory_swap`, `pids_limit`, and `ulimits`, so the values are lost in the Molecule
Podman adapter rather than Podman or the Ansible collection.

## Control test using `extra_opts`

Adding:


extra_opts:
  - --memory=268435456
  - --memory-swap=536870912
  - --pids-limit=1234


and recreating the container produced:


Memory=268435456
MemorySwap=536870912
PidsLimit=1234
Ulimits=[
  {"Name":"RLIMIT_NOFILE","Soft":4096,"Hard":4096},
  {"Name":"RLIMIT_NPROC","Soft":8192,"Hard":8192}
]


This confirms Podman accepts the limits and isolates the omission to the bundled
Molecule Podman create playbook.

## Expected behavior

The Podman driver should either:

1. Forward these platform fields to `podman_container`, consistently with the
   Docker driver and the underlying module; or
2. Validate/reject unsupported platform fields instead of silently ignoring them,
   and document `extra_opts` as the required interface.

Preferred mapping:


memory: "{{ item.memory | default(omit) }}"
memory_swap: "{{ item.memory_swap | default(omit) }}"
pids_limit: "{{ item.pids_limit | default(omit) }}"


## Workaround

Use per-platform `extra_opts`:


extra_opts:
  - --memory=4g
  - --memory-swap=4g
  - --pids-limit=16384


`ulimits` can continue using the native platform field:


ulimits:
  - nofile=65536:65536
  - nproc=16384:16384


Do not conflate `nproc` with `pids_limit`: `nproc` is an RLIMIT passed through
`ulimits`, while `pids_limit` controls the container's cgroup PID limit.