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Kubernetes alternatives to docker commands

Context​

Nowadays, Docker environment is very common in the software engineering:

  • most of the getting started explain how to start the official image of the software in your local docker engine
  • most of the engineering environments, especially on the software developer laptops, includes docker engine
  • Docker has been launch a long time before kubernetes

However, Docker suffers from several limitations:

  • the docker licensing model has changed, forcing some enterprise to subscribe to expensive licenses
  • kubernetes brings additional concepts that are not include with docker, such as ingresses or storage classes
  • limited high availability

That's why in some cases, it could be interesting to adapt some very common docker commands to kubernetes; and then benefits from k8saas.

Docker pull​

Docker pull downloads a docker image from a remote artefact repository to your internal docker artefact repository:

docker pull repository name/docker image name

ex:

docker pull wallarm/gotestwaf

The kubernetes alternative consists of downloading the docker image and starting the image on your remote kubernetes cluster using an infinite loop:

kubectl create deployment --image=repository name/docker image name kubernetes deployment name -- /bin/sh -ec "while :; do echo '.'; sleep 5 ; done"

ex:

# in default namespace
kubectl create deployment --image=wallarm/gotestwaf gotestwaf -- /bin/sh -ec "while :; do echo '.'; sleep 5 ; done"

# in dev namespace
kubectl hns create dev -n customer-namespaces
kubectl create deployment --image=wallarm/gotestwaf gotestwaf -n dev -- /bin/sh -ec "while :; do echo '.'; sleep 5 ; done"
caution

this method works only if your docker image contains /bin/sh

Docker run​

Docker run command starts the image and execute the command you requests.

docker run repository name/docker image name command args

ex:

docker run wallarm/gotestwaf /app/gotestwaf --url=https://MY_URL.com

The kubernetes alternatives just executes the command you request directly on the running container.

kubectl exec -it docker pod name -- command args

ex:

kubectl -n dev -c gotestwaf exec -it gotestwaf-757955bdcf-bkkr7 -- /app/gotestwaf --url=https://MY_URL.com
note

in the previous example:

  • the namespace is dev
  • the pod contains multiple containers, so the container must be specified with -c
  • pod name is different from deployment name. Check the correct name using kubectl get pods

Tips​

Copy remote files to local​

If you use the previous commands, you may need to get access to generated files on the container. To do so:

kubectl cp namespace/docker pod name:/YOUR_ABSOLUTE_PATH LOCAL_PATH

ex:

kubectl -n dev cp dev/gotestwaf-757955bdcf-bkkr7:/app/reports/waf-evaluation-report-2022-May-03-09-25-35.pdf /tmp/waf-evaluation-report-2022-May-03-09-25-35.pdf -c gotestwaf
caution

kubectl cp should be used only to get only small files (few MBs)