OpenShift Container Platform

Set the default maximum container root partition size for Overlay with CRI-O

You can use a ContainerRuntimeConfig custom resource (CR) to set a maximum partition size for the root disk of all containers.

The root partition of each container shows all of the available disk space of the underlying host.

To configure the maximum Overlay size, as well as other CRI-O options like the log level, you can create the following ContainerRuntimeConfig custom resource definition (CRD):

apiVersion: machineconfiguration.openshift.io/v1
kind: ContainerRuntimeConfig
metadata:
 name: overlay-size
spec:
 machineConfigPoolSelector:
   matchLabels:
     custom-crio: overlay-size
 containerRuntimeConfig:
   logLevel: debug
   overlaySize: 8G

Procedure

Create the configuration object:
```
$ oc apply -f overlaysize.yml
```
To apply the new CRI-O configuration to your worker nodes, edit the worker machine config pool:
```
$ oc edit machineconfigpool worker
```

Add the custom-crio label based on the matchLabels name you set in the ContainerRuntimeConfig CRD:

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfigPool
metadata:
  creationTimestamp: "2020-07-09T15:46:34Z"
  generation: 3
  labels:
    custom-crio: overlay-size
    machineconfiguration.openshift.io/mco-built-in: ""

Save the changes, then view the machine configs:

$ oc get machineconfigs

New 99-worker-generated-containerruntime and rendered-worker-xyz objects are created:

Example output

99-worker-generated-containerruntime  4173030d89fbf4a7a0976d1665491a4d9a6e54f1   3.5.0             7m42s
rendered-worker-xyz                   4173030d89fbf4a7a0976d1665491a4d9a6e54f1   3.5.0             7m36s

After those objects are created, monitor the machine config pool for the changes to be applied:

$ oc get mcp worker

The worker nodes show UPDATING as True, as well as the number of machines, the number updated, and other details:

Example output

NAME   CONFIG              UPDATED   UPDATING   DEGRADED  MACHINECOUNT  READYMACHINECOUNT  UPDATEDMACHINECOUNT   DEGRADEDMACHINECOUNT   AGE
worker rendered-worker-xyz False True False     3             2                   2                    0                      20h

When complete, the worker nodes transition back to UPDATING as False, and the UPDATEDMACHINECOUNT number matches the MACHINECOUNT:

Example output

NAME   CONFIG              UPDATED   UPDATING   DEGRADED  MACHINECOUNT  READYMACHINECOUNT  UPDATEDMACHINECOUNT   DEGRADEDMACHINECOUNT   AGE
worker   rendered-worker-xyz   True      False      False      3         3            3             0           20h

Looking at a worker machine, you see that the new 8 GB max size configuration is applied to all of the workers:

Example output

head -n 7 /etc/containers/storage.conf
[storage]
  driver = "overlay"
  runroot = "/var/run/containers/storage"
  graphroot = "/var/lib/containers/storage"
  [storage.options]
    additionalimagestores = []
    size = "8G"

Looking inside a container, you see that the root partition is now 8 GB:

Example output

~ $ df -h
Filesystem                Size      Used Available Use% Mounted on
overlay                   8.0G      8.0K      8.0G   0% /