Conventionally, container engines come equipped with a command-line tool to help users debug applications and simplify troubleshooting. For instance, when Docker is employed as the container runtime, you can use the docker command to inspect the status of containers and images and verify the accuracy of a container's configuration. But what if you're using other container engines? Here's when crictl comes in as an outstanding substitute for the docker tool.
Crictl is a part of cri-tools and functions much like the docker command line. It offers the direct advantage of being able to communicate with the container runtime via CRI, without the need for Kubelet. Designed specifically for Kubernetes, it is efficient at managing resources such as Pods, containers, and images. It aids both developers and users in debugging application issues and troubleshooting anomalies. Crictl can be used with all container runtimes implementing CRI interfaces.
But don't mistake crictl as a substitution for kubectl; it solely communicates with the container runtime via the CRI and is useful for debugging and troubleshooting, not for executing containers. While crictl does have commands to run Pods and containers, it's recommended to use them for debugging purposes only. Be cautious; if you create new Pods on a Kubernetes Node, Kubelet will stop and delete them.
Moving beyond crictl, cri-tools also provides a validation test tool critest, which checks whether the container runtime has implemented the necessary CRI features. Critest ensures that the implementation of the container runtime aligns with Kubelet's requirements by conducting an array of tests. This highly recommended tool should run its tests on all container runtimes before release. In most cases, critest is a part of integrated container runtime testing, ensuring that any code updates won't damage CRI functionality.
$ crictl ps -a
CONTAINER ID IMAGE CREATED STATE NAME ATTEMPT
1f73f2d81bf98 busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47 7 minutes ago Running sh 1
9c5951df22c78 busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47 8 minutes ago Exited sh 0
87d3992f84f74 nginx@sha256:d0a8828cccb73397acb0073bf34f4d7d8aa315263f1e7806bf8c55d8ac139d5f 8 minutes ago Running nginx 0
1941fb4da154f k8s-gcrio.azureedge.net/hyperkube-amd64@sha256:00d814b1f7763f4ab5be80c58e98140dfc69df107f253d7fdd714b30a714260a 18 hours ago Running kube-proxy 0
$ crictl exec -i -t 1f73f2d81bf98 ls
bin dev etc home proc root sys tmp usr var
