feat: add possibility to customize containerd with additional files

docs/runtime.md

@@ -42,6 +42,22 @@ Finally, if you want to change CRI look into:
     runtime = "runc"
 ```
 
+### Alternative method
+
+In case you don't want to change the original `/etc/k0s/containerd.toml` file, then you can easily add your customizations under the `/etc/k0s/containerd.d/` directory.
+
+Files under this path must have a `.toml` extention in order to get read by containerd:
+
+```shell
+cat << EOF > /etc/k0s/containerd.d/debug.toml
+[debug]
+  address = "/run/containerd/debug.sock"
+  uid = 0
+  gid = 0
+  level = "info"
+EOF
+```
+
 ## Using gVisor
 
 [gVisor](https://gvisor.dev/docs/) is an application kernel, written in Go, that implements a substantial portion of the Linux system call interface. It provides an additional layer of isolation between running applications and the host operating system.

pkg/component/worker/containerd.go

@@ -32,13 +32,17 @@ import (
 	"github.com/k0sproject/k0s/pkg/supervisor"
 )
 
-const confTmpl = `
+const confPath = "/etc/k0s/containerd.toml"
+const confPathContainerd = "/etc/k0s/containerd.d"
+
+var confTmpl = fmt.Sprintf(`
 # This is a placeholder configuration for k0s managed containerD.
 # If you wish to customize the config replace this file with your custom configuration.
 # For reference see https://github.com/containerd/containerd/blob/main/docs/man/containerd-config.toml.5.md
 version = 2
-`
-const confPath = "/etc/k0s/containerd.toml"
+
+imports = ["%s/*.toml"]
+`, confPathContainerd)
 
 // ContainerD implement the component interface to manage containerd as k0s component
 type ContainerD struct {
@@ -98,6 +102,9 @@ func (c *ContainerD) setupConfig() error {
 	if err := dir.Init(filepath.Dir(confPath), 0755); err != nil {
 		return err
 	}
+	if err := dir.Init(confPathContainerd, 0755); err != nil {
+		return err
+	}
 	return file.WriteContentAtomically(confPath, []byte(confTmpl), 0644)
 }