containerd, crictl, ctr

[Justin Hopper]

Hello,

I'm sure this will be a question that comes up a lot as Kubernetes uses switch away from Docker and to just containerd.  Most documentation references crictl for interacting with container runtimes, and I had been used to using that after leaving the docker cli.  However, just recently I noticed that ctr was there and ships with containerd. Why use crictl when there's ctr, I thought?

Well, the first problem I see, that must simply be a misconfiguration on my end, is that while crictl properly lists images and pods, ctr gives me nothing.  All while talking to the same containerd socket.

cat /etc/crictl.yaml 

runtime-endpoint: unix:///run/containerd/containerd.sock

image-endpoint: unix:///run/containerd/containerd.sock

timeout: 10

debug: true

crictl version

DEBU[0000] VersionRequest: &VersionRequest{Version:v1alpha2,} 

DEBU[0000] VersionResponse: &VersionResponse{Version:0.1.0,RuntimeName:containerd,RuntimeVersion:v1.4.1,RuntimeApiVersion:v1alpha2,} 

Version:  0.1.0

RuntimeName:  containerd

RuntimeVersion:  v1.4.1

RuntimeApiVersion:  v1alpha2

/opt/bin/ctr version

Client:

  Version:  v1.4.1

  Revision: c623d1b36f09f8ef6536a057bd658b3aa8632828

  Go version: go1.13.15

Server:

  Version:  v1.4.1

  Revision: c623d1b36f09f8ef6536a057bd658b3aa8632828

  UUID: 3afdd32d-747d-4ef3-b051-41922ff6afb0

ctr says the default socket location is, correctly: /run/containerd/containerd.sock

But doing a simple image list with ctr returns:

/opt/bin/ctr images ls

REF TYPE DIGEST SIZE PLATFORMS LABELS

But yet with crictl:

crictl images

DEBU[0000] <...snip> 

IMAGE                                TAG                 IMAGE ID            SIZE

k8s.gcr.io/coredns                   1.6.7               67da37a9a360e       13.6MB

k8s.gcr.io/etcd                      3.4.3-0             303ce5db0e90d       101MB

k8s.gcr.io/kube-apiserver            v1.18.9             e9585e7d08492       51.1MB

<...snip>

Having no experience with ctr prior to this, I'm thinking something is misconfigured for it, but I'm not sure what?  Also, interesting that ctr supports listing containers, but crictl only supports listing by pods, so it's of note that they don't seem to provide the same functionality.

Thanks,

Justin

[Rodrigo Campos]

On Thu, Dec 10, 2020 at 9:11 PM Justin Hopper <justin....@gmail.com> wrote:
>
> Well, the first problem I see, that must simply be a misconfiguration on my end, is that while crictl properly lists images and pods, ctr gives me nothing. All while talking to the same containerd socket.

containerd uses namespaces. Images, containers, etc. created via the
CRI are in one namespace (usually it is called k8s.io IIRC).

> But doing a simple image list with ctr returns:
> /opt/bin/ctr images ls
> REF TYPE DIGEST SIZE PLATFORMS LABELS
>

If you list the namespaces with cri, then choose the one about
kubernetes and list the images as you did, but specifying the
namespace, you will see them there :)


Rodrigo Campos
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