Disable discard_unpacked_layers for containerd >= 2.1 (#12821)

Only set `discard_unpacked_layers` in the CRI image config for containerd
versions earlier than 2.1.0.

Starting with containerd v2.1, the CRI plugin uses the Transfer Service for
image pulls by default. The `discard_unpacked_layers` option is incompatible
with the Transfer Service and triggers containerd to fall back to local
image pulls, logging a warning.

This change prevents unsupported configuration from being applied on newer
containerd versions, avoiding runtime warnings and ensuring default image
pull behavior.

Signed-off-by: Ali Afsharzadeh <afsharzadeh8@gmail.com>

Author: guoard

roles/container-engine/containerd/defaults/main.yml

@@ -35,8 +35,8 @@ containerd_default_base_runtime_spec_patch:
         hard: "{{ containerd_base_runtime_spec_rlimit_nofile }}"
         soft: "{{ containerd_base_runtime_spec_rlimit_nofile }}"
 
-# Can help reduce disk usage
-# https://github.com/containerd/containerd/discussions/6295
+# Only for containerd < 2.1; discard unpacked layers to save disk space
+# https://github.com/containerd/containerd/blob/release/2.1/docs/cri/config.md#image-pull-configuration-since-containerd-v21
 containerd_discard_unpacked_layers: true
 
 containerd_base_runtime_specs:

roles/container-engine/containerd/templates/config.toml.j2

@@ -76,7 +76,9 @@ oom_score = {{ containerd_oom_score }}
 
   [plugins."io.containerd.cri.v1.images"]
     snapshotter = "{{ containerd_snapshotter }}"
+{% if containerd_discard_unpacked_layers and containerd_version is version('2.1.0', '<') %}
     discard_unpacked_layers = {{ containerd_discard_unpacked_layers | lower }}
+{% endif %}
     image_pull_progress_timeout = "{{ containerd_image_pull_progress_timeout }}"
   [plugins."io.containerd.cri.v1.images".pinned_images]
     sandbox = "{{ pod_infra_image_repo }}:{{ pod_infra_image_tag }}"