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Customizing nodes - Installation configuration | Installing | OpenShift Container Platform 4.4
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Customizing nodes

Although directly making changes to OpenShift Container Platform nodes is discouraged, there are times when it is necessary to implement a required low-level security, networking, or performance feature. Direct changes to OpenShift Container Platform nodes can be done by:

  • Creating machine configs that are included in manifest files to start up a cluster during openshift-install.

  • Creating machine configs that are passed to running OpenShift Container Platform nodes via the Machine Config Operator.

The following sections describe features that you might want to configure on your nodes in this way.

Adding day-1 kernel arguments

ALthough it is often preferable to modify kernel arguments as a day-2 activity, you might want to add kernel arguments to all master or worker nodes during initial cluster installation. Here are some reasons you might want to add kernel arguments during cluster installation so they take effect before the systems first boot up:

  • You want to disable a feature, such as SELinux, so it has no impact on the systems when they first come up.

  • You need to do some low-level network configuration before the systems start.

To add kernel arguments to master or worker nodes, you can create a MachineConfig object and inject that object into the set of manifest files used by Ignition during cluster setup.

For a listing of arguments you can pass to a RHEL 8 kernel at boot time, see Kernel.org kernel parameters. It is best to only add kernel arguments with this procedure if they are needed to complete the initial OpenShift Container Platform installation.

Procedure

  1. Generate the Kubernetes manifests for the cluster:

    $ ./openshift-install create manifests --dir=<installation_directory>

  2. Decide if you want to add kernel arguments to worker or master nodes.

  3. In the openshift directory, create a file (for example, 99-openshift-machineconfig-master-kargs.yaml) to define a MachineConfig object to add the kernel settings. This example adds a loglevel=7 kernel argument to master nodes:

    $ cat << EOF > 99-openshift-machineconfig-master-kargs.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: master
  name: 99-openshift-machineconfig-master-kargs
spec:
  kernelArguments:
    - 'loglevel=7'
EOF

    You can change master to worker to add kernel arguments to worker nodes instead. Create a separate YAML file to add to both master and worker nodes.

You can now continue on to create the cluster.

Adding kernel modules to nodes

For most common hardware, the Linux kernel includes the device driver modules needed to use that hardware when the computer starts up. For some hardware, however, modules are not available in Linux. Therefore, you must find a way to provide those modules to each host computer. This procedure describes how to do that for nodes in an OpenShift Container Platform cluster.

When a kernel module is first deployed by following these instructions, the module is made available for the current kernel. If a new kernel is installed, the kmods-via-containers software will rebuild and deploy the module so a compatible version of that module is available with the new kernel.

The way that this feature is able to keep the module up to date on each node is by:

  • Adding a systemd service to each node that starts at boot time to detect if a new kernel has been installed and

  • If a new kernel is detected, the service rebuilds the module and installs it to the kernel

For information on the software needed for this procedure, see the kmods-via-containers github site.

A few important issues to keep in mind:

  • This procedure is Technology Preview.

  • Software tools and examples are not yet available in official RPM form and can only be obtained for now from unofficial github.com sites noted in the procedure.

  • Third-party kernel modules you might add through these procedures are not supported by Red Hat.

  • In this procedure, the software needed to build your kernel modules is deployed in a RHEL 8 container. Keep in mind that modules are rebuilt automatically on each node when that node gets a new kernel. For that reason, each node needs access to a yum repository that contains the kernel and related packages needed to rebuild the module. That content is best provided with a valid RHEL subscription.

Building and testing the kernel module container

Before deploying kernel modules to your OpenShift Container Platform cluster, you can test the process on a separate RHEL system. Gather the kernel module’s source code, the KVC framework, and the kmod-via-containers software. Then build and test the module. To do that on a RHEL 8 system, do the following:

Procedure

  1. Get a RHEL 8 system, then register and subscribe it:

    # subscription-manager register
Username: yourname
Password: ***************
# subscription-manager attach --auto

  2. Install software needed to build the software and container:

    # yum install podman make git -y

  3. Clone the kmod-via-containers repository:

    $ mkdir kmods; cd kmods
$ git clone https://github.com/kmods-via-containers/kmods-via-containers

  4. Install a KVC framework instance on your RHEL 8 build host to test the module. This adds a kmods-via-container systemd service and loads it:

    $ cd kmods-via-containers/
$ sudo make install
$ sudo systemctl daemon-reload

  5. Get the kernel module source code. The source code might be used to build a third-party module that you do not have control over, but is supplied by others. You will need content similar to the content shown in the kvc-simple-kmod example that can be cloned to your system as follows:

    $ cd ..
$ git clone https://github.com/kmods-via-containers/kvc-simple-kmod

  6. Edit the configuration file, simple-kmod.conf, in his example, and change the name of the Dockerfile to Dockerfile.rhel so the file appears as shown here:

    $ cd kvc-simple-kmod
$ cat simple-kmod.conf

KMOD_CONTAINER_BUILD_CONTEXT="https://github.com/kmods-via-containers/kvc-simple-kmod.git"
KMOD_CONTAINER_BUILD_FILE=Dockerfile.rhel
KMOD_SOFTWARE_VERSION=dd1a7d4
KMOD_NAMES="simple-kmod simple-procfs-kmod"

  7. Create an instance of kmods-via-containers@.service for your kernel module, simple-kmod in this example, and enable it:

    $ sudo make install
$ sudo kmods-via-containers build simple-kmod $(uname -r)

  8. Enable and start the systemd service, then check the status:

    $ sudo systemctl enable kmods-via-containers@simple-kmod.service
$ sudo systemctl start kmods-via-containers@simple-kmod.service
$ sudo systemctl status kmods-via-containers@simple-kmod.service
● kmods-via-containers@simple-kmod.service - Kmods Via Containers - simple-kmod
   Loaded: loaded (/etc/systemd/system/kmods-via-containers@.service;
          enabled; vendor preset: disabled)
   Active: active (exited) since Sun 2020-01-12 23:49:49 EST; 5s ago...

  9. To confirm that the kernel modules are loaded, use the lsmod command to list the modules:

    $ lsmod | grep simple_
simple_procfs_kmod     16384  0
simple_kmod            16384  0

  10. The simple-kmod example has a few other ways to test that it is working. Look for a "Hello world" message in the kernel ring buffer with dmesg:

    $ dmesg | grep 'Hello world'
[ 6420.761332] Hello world from simple_kmod.

    Check the value of simple-procfs-kmod in /proc:

    $ sudo cat /proc/simple-procfs-kmod
simple-procfs-kmod number = 0

    Run the spkut command to get more information from the module:

    $ sudo spkut 44
KVC: wrapper simple-kmod for 4.18.0-147.3.1.el8_1.x86_64
Running userspace wrapper using the kernel module container...
+ podman run -i --rm --privileged
   simple-kmod-dd1a7d4:4.18.0-147.3.1.el8_1.x86_64 spkut 44
simple-procfs-kmod number = 0
simple-procfs-kmod number = 44

Going forward, when the system boots this service will check if a new kernel is running. If there is a new kernel, the service builds a new version of the kernel module and then loads it. If the module is already built, it will just load it.

Provisioning a kernel module to OpenShift Container Platform

Depending on whether or not you must have the kernel module in place when OpenShift Container Platform cluster first boots, you can set up the kernel modules to be deployed in one of two ways:

  • Provision kernel modules at cluster install time (day-1): You can create the content as a MachineConfig object and provide it to openshift-install by including it with a set of manifest files.

  • Provision kernel modules via Machine Config Operator (day-2): If you can wait until the cluster is up and running to add your kernel module, you can deploy the kernel module software via the Machine Config Operator (MCO).

In either case, each node needs to be able to get the kernel packages and related software packages at the time that a new kernel is detected. There are a few ways you can set up each node to be able to obtain that content.

  • Provide RHEL entitlements to each node.

  • Get RHEL entitlements from an existing RHEL host, from the /etc/pki/entitlement directory and copy them to the same location as the other files you provide when you build your Ignition config.

  • Inside the Dockerfile, add pointers to a yum repository containing the kernel and other packages. This must include new kernel packages as they are needed to match newly installed kernels.

Provision kernel modules via a MachineConfig object

By packaging kernel module software with a MachineConfig object, you can deliver that software to worker or master nodes at installation time or via the Machine Config Operator.

First create a base Ignition config that you would like to use. At installation time, the Ignition config will contain the ssh public key to add to the authorized_keys file for the core user on the cluster. To add the MachineConfig object later via the MCO instead, the SSH public key is not required. For both type, the example simple-kmod service creates a systemd unit file, which requires a kmods-via-containers@simple-kmod.service.

The systemd unit is a workaround for an upstream bug and makes sure that the kmods-via-containers@simple-kmod.service gets started on boot:

  1. Get a RHEL 8 system, then register and subscribe it:

    # subscription-manager register
Username: yourname
Password: ***************
# subscription-manager attach --auto

  2. Install software needed to build the software:

    # yum install podman make git -y

  3. Create an Ignition config file that creates a systemd unit file:

    $ mkdir kmods; cd kmods
$ cat <<EOF > ./baseconfig.ign
{
  "ignition": { "version": "2.2.0" },
  "passwd": {
    "users": [
      {
        "name": "core",
        "groups": ["sudo"],
        "sshAuthorizedKeys": [
          "ssh-rsa AAAA"
        ]
      }
    ]
  },
  "systemd": {
    "units": [{
      "name": "require-kvc-simple-kmod.service",
      "enabled": true,
      "contents": "[Unit]\nRequires=kmods-via-containers@simple-kmod.service\n[service]\nType=oneshot\nExecStart=/usr/bin/true\n\n[Install]\nWantedBy=multi-user.target"
    }]
  }
}
EOF

    You must add your public SSH key to the baseconfig.ign file to use the file during openshift-install. The public SSH key is not needed if you create the MachineConfig object using the MCO.

  4. Create a base MCO YAML snippet that looks like:

$ cat <<EOF > mc-base.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 10-kvc-simple-kmod
spec:
  config:
EOF

+

The mc-base.yaml is set to deploy the kernel module on worker nodes. To deploy on master nodes, change the role from worker to master. To do both, you could repeat the whole procedure using different file names for the two types of deployments.

  1. Get the kmods-via-containers software:

    $ git clone https://github.com/kmods-via-containers/kmods-via-containers
$ git clone https://github.com/kmods-via-containers/kvc-simple-kmod

  2. Get your module software. In this example, kvc-simple-kmod is used:

  3. Create a fakeroot directory and populate it with files that you want to deliver via Ignition, using the repositories cloned earlier:

    $ FAKEROOT=$(mktemp -d)
$ cd kmods-via-containers
$ make install DESTDIR=${FAKEROOT}/usr/local CONFDIR=${FAKEROOT}/etc/
$ cd ../kvc-simple-kmod
$ make install DESTDIR=${FAKEROOT}/usr/local CONFDIR=${FAKEROOT}/etc/

  4. Get a tool called filetranspiler and dependent software:

    $ cd ..
$ sudo yum install -y python3
git clone https://github.com/ashcrow/filetranspiler.git

  5. Generate a final machine config YAML (mc.yaml) and have it include the base Ignition config, base machine config, and the fakeroot directory with files you would like to deliver:

    $ ./filetranspiler/filetranspile -i ./baseconfig.ign \
     -f ${FAKEROOT} --format=yaml --dereference-symlinks \
     | sed 's/^/     /' | (cat mc-base.yaml -) > 99-simple-kmod.yaml

  6. If the cluster is not up yet, generate manifest files and add this file to the openshift directory. If the cluster is already running, apply the file as follows:

    $ oc create -f 99-simple-kmod.yaml

    Your nodes will start the kmods-via-containers@simple-kmod.service service and the kernel modules will be loaded.

  7. To confirm that the kernel modules are loaded, you can log in to a node (using oc debug node/<openshift-node>, then chroot /host). To list the modules, use the lsmod command:

    $ lsmod | grep simple_
simple_procfs_kmod     16384  0
simple_kmod            16384  0

Encrypting disks during installation

During OpenShift Container Platform installation, you can enable disk encryption on all master and worker nodes. This feature:

  • Is available for installer-provisioned infrastructure and user-provisioned infrastructure deployments

  • Is supported on Red Hat Enterprise Linux CoreOS (RHCOS) systems only

  • Sets up disk encryption during the manifest installation phase so all data written to disk, from first boot forward, is encrypted

  • Encrypts data on the root filesystem only (/dev/mapper/coreos-luks-root on /)

  • Requires no user intervention for providing passphrases

  • Uses AES-256-CBC encryption

  • Should be enabled for your cluster to support FIPS.

There are two different supported encryption modes:

  • TPM v2: This is the preferred mode. TPM v2 stores passphrases in a secure cryptoprocessor. To implement TPM v2 disk encryption, create an Ignition config file as described below.

  • Tang: To use Tang to encrypt your cluster, you need to use a Tang server. Clevis implements decryption on the client side. Tang encryption mode is only supported for bare metal installs.

Follow one of the two procedures to enable disk encryption for the nodes in your cluster.

Enabling TPM v2 disk encryption

Use this procedure to enable TPM v2 mode disk encryption during OpenShift Container Platform deployment.

Procedure

  1. Check to see if TPM v2 encryption needs to be enabled in the BIOS on each node. This is required on most Dell systems. Check the manual for your computer.

  2. Generate the Kubernetes manifests for the cluster:

    $ ./openshift-install create manifests --dir=<installation_directory>

  3. In the openshift directory, create a master and/or worker file to encrypt disks for those nodes. Here are examples of those two files:

    $ cat << EOF > ./99-openshift-worker-tpmv2-encryption.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  name: worker-tpm
  labels:
    machineconfiguration.openshift.io/role: worker
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;base64,e30K
        filesystem: root
        mode: 420
        path: /etc/clevis.json
EOF
    $ cat << EOF > ./99-openshift-master-tpmv2-encryption.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  name: master-tpm
  labels:
    machineconfiguration.openshift.io/role: master
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;base64,e30K
        filesystem: root
        mode: 420
        path: /etc/clevis.json
EOF

  4. Make a backup copy of the YAML file. You should do this because the file will be deleted when you create the cluster.

  5. Continue with the remainder of the OpenShift Container Platform deployment.

Enabling Tang disk encryption

Use this procedure to enable Tang mode disk encryption during OpenShift Container Platform deployment.

Procedure

  1. Access a Red Hat Enterprise Linux server from which you can configure the encryption settings and run openshift-install to install a cluster and oc to work with it.

  2. Set up or access an existing Tang server. See Network-bound disk encryption for instructions. See Securing Automated Decryption New Cryptography and Techniques for a presentation on Tang.

  3. Add kernel arguments to configure networking when you do the Red Hat Enterprise Linux CoreOS (RHCOS) installations for your cluster. For example, to configure DHCP networking, identify ip=dhcp, or set static networking when you add parameters to the kernel command line. For both DHCP and static networking, you also must provide the rd.neednet=1 kernel argument.

Skipping this step causes the second boot to fail.

  1. Generate the thumbprint. Install the clevis package, it is not already installed, and generate a thumbprint from the Tang server. Replace the value of url with the Tang server URL:

    $ sudo yum install clevis -y
$ echo nifty random wordwords \
     | clevis-encrypt-tang \
       '{"url":"https://tang.example.org"}'

The advertisement contains the following signing keys:

PLjNyRdGw03zlRoGjQYMahSZGu9

Do you wish to trust these keys? [ynYN] y
eyJhbmc3SlRyMXpPenc3ajhEQ01tZVJiTi1oM...

  2. Create a Base64 encoded file, replacing the URL of the Tang server (url) and thumbprint (thp) you just generated:

    $ (cat <<EOM
{
 "url": "https://tang.example.com",
 "thp": "PLjNyRdGw03zlRoGjQYMahSZGu9"
}
EOM
) | base64 -w0

ewogInVybCI6ICJodHRwczovL3RhbmcuZXhhbXBsZS5jb20iLAogInRocCI6ICJaUk1leTFjR3cwN3psVExHYlhuUWFoUzBHdTAiCn0K

  3. Replace the “source” in the TPM2 example with the Base64 encoded file for one or both of these examples for worker and/or master nodes:

    You must add the rd.neednet=1 kernel argument.

    		 
    $ cat << EOF > ./99-openshift-worker-tang-encryption.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  name: worker-tang
  labels:
    machineconfiguration.openshift.io/role: worker
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;base64,e30K
          source: data:text/plain;base64,ewogInVybCI6ICJodHRwczovL3RhbmcuZXhhbXBsZS5jb20iLAogInRocCI6ICJaUk1leTFjR3cwN3psVExHYlhuUWFoUzBHdTAiCn0K
        filesystem: root
        mode: 420
        path: /etc/clevis.json
  kernelArguments:
    - rd.neednet=1 (1)
EOF
    1 Required. 
    $ cat << EOF > ./99-openshift-master-tang-encryption.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  name: master-tang
  labels:
    machineconfiguration.openshift.io/role: master
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
      - contents:
          source: data:text/plain;base64,e30K
          source: data:text/plain;base64,ewogInVybCI6ICJodHRwczovL3RhbmcuZXhhbXBsZS5jb20iLAogInRocCI6ICJaUk1leTFjR3cwN3psVExHYlhuUWFoUzBHdTAiCn0K
        filesystem: root
        mode: 420
        path: /etc/clevis.json
  kernelArguments:
    - rd.neednet=1 (1)
EOF
    1 Required.

  4. Continue with the remainder of the OpenShift Container Platform deployment.

Configuring chrony time service

You can set the time server and related settings used by the chrony time service (chronyd) by modifying the contents of the chrony.conf file and passing those contents to your nodes as a machine config.

Procedure

  1. Create the contents of the chrony.conf file and encode it as base64. For example:

    $ cat << EOF | base64
    server clock.redhat.com iburst
    driftfile /var/lib/chrony/drift
    makestep 1.0 3
    rtcsync
    logdir /var/log/chrony
    EOF

ICAgIHNlcnZlciBjbG9jay5yZWRoYXQuY29tIGlidXJzdAogICAgZHJpZnRmaWxlIC92YXIvbGli
L2Nocm9ueS9kcmlmdAogICAgbWFrZXN0ZXAgMS4wIDMKICAgIHJ0Y3N5bmMKICAgIGxvZ2RpciAv
dmFyL2xvZy9jaHJvbnkK

  2. Create the MachineConfig object file, replacing the base64 string with the one you just created yourself. This example adds the file to master nodes. You can change it to worker or make an additional MachineConfig object for the worker role:

    $ cat << EOF > ./masters-chrony-configuration.yaml
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: master
  name: masters-chrony-configuration
spec:
  config:
    ignition:
      config: {}
      security:
        tls: {}
      timeouts: {}
      version: 2.2.0
    networkd: {}
    passwd: {}
    storage:
      files:
      - contents:
          source: data:text/plain;charset=utf-8;base64,ICAgIHNlcnZlciBjbG9jay5yZWRoYXQuY29tIGlidXJzdAogICAgZHJpZnRmaWxlIC92YXIvbGliL2Nocm9ueS9kcmlmdAogICAgbWFrZXN0ZXAgMS4wIDMKICAgIHJ0Y3N5bmMKICAgIGxvZ2RpciAvdmFyL2xvZy9jaHJvbnkK
          verification: {}
        filesystem: root
        mode: 420
        path: /etc/chrony.conf
  osImageURL: ""
EOF

  3. Make a backup copy of the configuration file.

  4. If the cluster is not up yet, generate manifest files, add this file to the openshift directory, then continue to create the cluster.

  5. If the cluster is already running, apply the file as follows:

     $ oc apply -f ./masters-chrony-configuration.yaml

Additional resources

See Support for FIPS cryptography for information on FIPS support.