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29 April 2019

Modifying node configurations in OpenShift 4.X

by Juan Antonio Osorio Robles

OpenShift 4.X relies heavily on operators in order to configure… just about everything. This includes the configuration of the hosts that run the OpenShift installation. In order to configure the aforementioned hosts, the installation comes with a running instance of the “machine-config-operator”, which is an operator that applies host configurations and restarts the host whenever it detects configuration changes.

So, to learn how to use this, lets change /etc/chrony.conf and set up some specific servers.

First of all, lets look at the configuration we want to apply to chrony.conf:

server 0.fedora.pool.ntp.org
server 1.fedora.pool.ntp.org
server 2.fedora.pool.ntp.org
driftfile /var/lib/chrony/drift
makestep 1.0 3
rtcsync
keyfile /etc/chrony.keys
leapsectz right/UTC
logdir /var/log/chrony

This configuration is based on what’s shipped by default in OpenShift, except that we made the deployment get its time from the three specific fedora nodes in ntp.org.

Prerequisites

The machine-config-operator gives us a construct named MachineConfig, which allows us to apply configuration changes to specific files and to specific roles.

What are these roles?

Well, the machine-config-operator works with so called MachineConfigPools which are sets of nodes that have a specific role in your system. Most likely these nodes will run different services, and serve different purposes.

To view all of the roles in your system, do:

oc get machineconfigpools

In my basic deployment, I see the following:

NAME     CONFIG                                             UPDATED   UPDATING   DEGRADED
master   rendered-master-f0718d88f154089eae3b199e387696d4   True      False      False
worker   rendered-worker-3c907e9ae475284d33eadfa3bc6117a5   True      False      False

The main thing to note here are the names of the roles, which we’ll use in our configuration.

Another thing to note is that currently, the configurations need URL encoding in our MachineConfig definition.

For this, we can use the following snippet:

cat example-chrony.conf | python3 -c "import sys, urllib.parse; print(urllib.parse.quote(''.join(sys.stdin.readlines())))"

This will output the contents of the configuration file (in this case called exmaple-chrony.conf), and read it in a python script which will encode the contents, including newlines.

This will give us the following output:

server%200.fedora.pool.ntp.org%0Aserver%201.fedora.pool.ntp.org%0Aserver%202.fedora.pool.ntp.org%0Adriftfile%20/var/lib/chrony/drift%0Amakestep%201.0%203%0Artcsync%0Akeyfile%20/etc/chrony.keys%0Aleapsectz%20right/UTC%0Alogdir%20/var/log/chrony%0A

With this in mind, lets apply the aforementioned configuration!

Apply the configuration

apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 50-worker-chrony
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:,server%200.fedora.pool.ntp.org%0A%0Aserver%201.fedora.pool.ntp.org%0A%0Aserver%202.fedora.pool.ntp.org%0A%0Adriftfile%20/var/lib/chrony/drift%0A%0Amakestep%201.0%203%0A%0Artcsync%0A%0Akeyfile%20/etc/chrony.keys%0A%0Aleapsectz%20right/UTC%0A%0Alogdir%20/var/log/chrony%0A
        filesystem: root
        mode: 0644
        path: /etc/chrony.conf

We’ll call this yaml file chrony-enable-worker.yaml.

Note that we specified the role via the machineconfiguration.openshift.io/role label in the MachineConfig’s metadata. We also gave it a name that reflects the application order (50 will be applied in the middle), the role’s name, and the configuration we’re applying.

Lets see all of the MachineConfig objects that are currently applied to our system:

$ oc get machineconfigs                                                                                                                                                                              
NAME                                                        GENERATEDBYCONTROLLER               IGNITIONVERSION   CREATED
00-master                                                   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
00-worker                                                   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
01-master-container-runtime                                 4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
01-master-kubelet                                           4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
01-worker-container-runtime                                 4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
01-worker-kubelet                                           4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
99-master-1f70153f-6a5e-11e9-ae85-021543e42872-registries   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
99-master-ssh                                                                                   2.2.0             72m
99-worker-1f718afb-6a5e-11e9-ae85-021543e42872-registries   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
99-worker-ssh                                                                                   2.2.0             72m
rendered-master-f0718d88f154089eae3b199e387696d4            4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m
rendered-worker-591c18e125b4a536c8574ca84da362f6            4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             71m

Lets now apply our configuration

oc create -f chrony-enable-worker.yaml

Having applied our changes, we’ll see that the new configuration applies fairly in the middle:

NAME                                                        GENERATEDBYCONTROLLER               IGNITIONVERSION   CREATED
00-master                                                   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
00-worker                                                   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
01-master-container-runtime                                 4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
01-master-kubelet                                           4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
01-worker-container-runtime                                 4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
01-worker-kubelet                                           4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
50-worker-chrony                                                                                2.2.0             13s
99-master-1f70153f-6a5e-11e9-ae85-021543e42872-registries   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             73m
99-master-ssh                                                                                   2.2.0             73m
99-worker-1f718afb-6a5e-11e9-ae85-021543e42872-registries   4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             73m
99-worker-ssh                                                                                   2.2.0             73m
rendered-master-f0718d88f154089eae3b199e387696d4            4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m
rendered-worker-591c18e125b4a536c8574ca84da362f6            4.0.0-alpha.0-269-g0ae25d4c-dirty   2.2.0             72m

Going back to our MachineConfig declaration, lets also note that the configuration was applied to the source key, and had the data:, prefix in it. This details are important things to remember if you want your configuration to be applied correctly, as they’re things that the machine-config-operator expects.

If we want to apply the configuration to other hosts, we’ll need a MachineConfig object per-role (This might be fixed in the future).

Verifying our configuration changes

Lets log into our node to check that the changes were successfully applied (Note that it might take some time for the changes to apply, since they need to be picked up by the operator first).

Lets first choose one node to view.

To check the nodes in your system, do:

$ oc get nodes
NAME                                         STATUS   ROLES    AGE   VERSION
ip-10-0-135-81.eu-west-1.compute.internal    Ready    master   96m   v1.13.4+4fd195e58
ip-10-0-138-158.eu-west-1.compute.internal   Ready    worker   89m   v1.13.4+4fd195e58
ip-10-0-154-149.eu-west-1.compute.internal   Ready    worker   89m   v1.13.4+4fd195e58
ip-10-0-157-220.eu-west-1.compute.internal   Ready    master   95m   v1.13.4+4fd195e58
ip-10-0-169-234.eu-west-1.compute.internal   Ready    worker   89m   v1.13.4+4fd195e58
ip-10-0-173-147.eu-west-1.compute.internal   Ready    master   96m   v1.13.4+4fd195e58

Notice that the roles of the host are specified in their own column.

So, given that it’s a worker node, lets choose ip-10-0-138-158.eu-west-1.compute.internal.

To log into the node, we do:

$ oc debug node/ip-10-0-138-158.eu-west-1.compute.internal
$ chroot /host

Once in the node, you can do the following command:

chronyc -4 -n sources

This should show that there are 3 sources that chronyd is using, and the IP addresses to all of them.

The ultimate source of truth

Another feature of the machine-config-operator, is that it allows you to query an aggregated structure with all of the configurations that have been rendered into the host.

Remember the output of getting the MachineConfigPools? Lets get it again:

oc get machineconfigpools                                                                                                                                                                          
NAME     CONFIG                                             UPDATED   UPDATING   DEGRADED
master   rendered-master-f8b48d03fe36cf056b547e294deafb44   True      False      False
worker   rendered-worker-3c907e9ae475284d33eadfa3bc6117a5   True      False      False

You will note two things:

To look at the render, we can do the following:

oc get machineconfig/rendered-worker-3c907e9ae475284d33eadfa3bc6117a5 -o yaml

This will show us a yaml representation of all of the configurations that have been applied to that role.

tags: openshift

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