Dream IT Enterprises

Tag: tips

  • Add `allowVolumeExpansion: true` to your storage class

    StorageClass

    If you have a Kubernetes cluster running for couple of years, you would probably have legacy StorageClass defined which does not contain allowVolumeExpansion: true bit set. If this bit is not set on your storageClass, then you cannot expand your PVCs which are using this storageClass.

    But, if you try to edit storage class to add this attribute to the specs, kubernetes does not allow you to do so saying that this field is immutable and cannot be changed after definition.

    So now, how do we expand these PVCs which are created using legacy storage class without allowVolumeExpansion bit set?

    It turns out – its quite easy. You can delete your old storage class without affecting your PVCs. And recreate it again, with same name, but this time with allowVolumeExpansion: true in the sepcs.

    Now the old PVCs which were creating using the said StorageClass can now be expanded, automatically!!

    That’s it for today!

  • push / pull images without Docker

    Increasingly, docker is being replaced with containerd in kubernetes clusters. These days, in my daily work, I am dealing with clusters almost exclusively with containerd as CRI. In such cases, sometimes there is a need to pull or push some images to say, internal / private registries. without docker cli installed and docker daemon running, how do we achieve this? Read on.

    Option 1 – use ctr – the containerd CLI

    ContainerD gets installed with its own CLI – ctr – which is lot more minimal than docker cli. But fortunately, push and pull commands are available. I am yet to find a way to see the logs and exec into a containers ( at least in v1.4)

    # pull image using ctr 
sudo ctr i pull docker.io/utkuozdemir/pv-migrate-sshd:1.0.0

# tag the image for your internal container registry
sudo ctr i tag docker.io/utkuozdemir/pv-migrate-sshd:1.0.0 my-internal-nexus:5002/pv-migrate-sshd:1.0.0

# Push to internal container registry server
sudo ctr i push --platform linux/amd64 my-internal-nexus:5002/pv-migrate-sshd:1.0.0

    One thing to remember about ctr is that it expects that you have image for all the platforms to push. If you have downloaded the image, it would only be for one platform say.. linux-amd64. So in push command, we must specify --platform linux/amd64. If we don’t do this, ctr push command fails with very cryptic error about not having image content.

    Option 2 – use crictl

    kubernetes CRI team has created crictl which you can download and install and it provides docker like CLI to deal with containers.

    crictl is certainly much easier to use than ctr but downloading arbitary things on your servers is not an option in many places, rightfully, due to security concerns. In such cases, ctr is the only option you are left with.

    That’s it for now.