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Configuration

The MicroShift configuration file must be located at /etc/microshift/config.yaml. A sample /etc/microshift/config.yaml.default configuration file is installed by the MicroShift RPM and it can be used as a template when customizing MicroShift.

The format of the config.yaml configuration file is as follows.

apiServer:
    advertiseAddress: ""
    auditLog:
        maxFileAge: 0
        maxFileSize: 0
        maxFiles: 0
        profile: ""
    namedCertificates:
        - certPath: ""
          keyPath: ""
          names:
            - ""
    subjectAltNames:
        - ""
debugging:
    logLevel: ""
dns:
    baseDomain: ""
etcd:
    memoryLimitMB: 0
ingress:
    listenAddress:
        - ""
    ports:
        http: 0
        https: 0
    routeAdmissionPolicy:
        namespaceOwnership: ""
    status: ""
kubelet:
manifests:
    kustomizePaths:
        - ""
network:
    clusterNetwork:
        - ""
    serviceNetwork:
        - ""
    serviceNodePortRange: ""
node:
    hostnameOverride: ""
    nodeIP: ""
    nodeIPv6: ""
storage:
    driver: ""
    optionalCsiComponents:
        - ""

Default Settings

In case config.yaml is not provided, the following default settings will be used.

apiServer:
    advertiseAddress: ""
    auditLog:
        maxFileAge: 0
        maxFileSize: 200
        maxFiles: 10
        profile: Default
    namedCertificates:
        - certPath: ""
          keyPath: ""
          names:
            - ""
    subjectAltNames:
        - ""
debugging:
    logLevel: Normal
dns:
    baseDomain: example.com
etcd:
    memoryLimitMB: 0
ingress:
    listenAddress:
        - ""
    ports:
        http: 80
        https: 443
    routeAdmissionPolicy:
        namespaceOwnership: InterNamespaceAllowed
    status: Managed
kubelet:
manifests:
    kustomizePaths:
        - /usr/lib/microshift/manifests
        - /usr/lib/microshift/manifests.d/*
        - /etc/microshift/manifests
        - /etc/microshift/manifests.d/*
network:
    clusterNetwork:
        - 10.42.0.0/16
    serviceNetwork:
        - 10.43.0.0/16
    serviceNodePortRange: 30000-32767
node:
    hostnameOverride: ""
    nodeIP: ""
    nodeIPv6: ""
storage:
    driver: ""
    optionalCsiComponents:
        - ""

Service NodePort range

The serviceNodePortRange setting allows the extension of the port range available to NodePort Services. This option is useful when specific standard ports under the 30000-32767 need to be exposed. i.e., your device needs to expose the 1883/tcp MQTT port on the network because some client devices cannot use a different port.

If you use this option, you must be careful; NodePorts can overlap with system ports, causing malfunction of the system or MicroShift. Take the following considerations into account:

  • Do not create any NodePort service without an explicit nodePort selection, in this case the port is assigned randomly by the kube-apiserver.
  • Do not create any NodePort service for any system service port, MicroShift port, or other services you expose on your device HostNetwork.

List of ports that you must avoid:

Port Description
22/tcp SSH port
80/tcp OpenShift Router HTTP endpoint
443/tcp OpenShift Router HTTPS endpoint
1936/tcp Metrics service for the openshift-router, not exposed today
2379/tcp etcd port
2380/tcp etcd port
6443 kubernetes API
8445/tcp openshift-route-controller-manager
9537/tcp cri-o metrics
10250/tcp kubelet
10248/tcp kubelet healthz port
10259/tcp kube scheduler
--------------- -----------------------------------------------------------------

Etcd Memory Limit

By default, etcd will be allowed to use as much memory as it needs to handle the load on the system; however, in memory constrained systems, it may be preferred or necessary to limit the amount of memory etcd is allowed to use at a given time.

Setting the memoryLimitMB to a value greater than 0 will result in a soft memory limit being applied to etcd; etcd will be allowed to go over this value during operation, but memory will be more aggresively reclaimed from it if it does. A value of 128 megabytes is the configuration floor - attempting to set the limit below 128 megabytes will result in the configuration being 128 megabytes.

Please note that values close to the floor may be more likely to impact etcd performance - the memory limit is a trade-off of memory footprint and etcd performance. The lower the limit, the more time etcd will spend on paging memory to disk and will take longer to respond to queries or even timing requests out if the limit is low and the etcd usage is high.

Auto-applying Manifests

MicroShift leverages kustomize for Kubernetes-native templating and declarative management of resource objects. Upon start-up, it searches /etc/microshift/manifests, /etc/microshift/manifests.d/*, /usr/lib/microshift/manifests, and /usr/lib/microshift/manifests.d/* directories for a kustomization.yaml, kustomization.yml, or Kustomization file. If it finds one, it automatically runs kubectl apply -k command to apply that manifest.

Loading from multiple directories allows you to manage MicroShift workloads more flexibly. Different workloads can be independent of each other, instead of having to be loaded from a merged set of inputs.

Location Intent
/etc/microshift/manifests Read-write location for configuration management systems or development
/etc/microshift/manifests.d/* Read-write location for configuration management systems or development
/usr/lib/microshift/manifests Read-only location for embedding configuration manifests on ostree based systems
/usr/lib/microshift/manifestsd./* Read-only location for embedding configuration manifests on ostree based systems

To override the list of paths, set manifests.kustomizePaths in the configuration file.

manifests:
    kustomizePaths:
        - "/opt/alternate/path"

The values of kustomizePaths may be glob patterns.

manifests:
    kustomizePaths:
        - "/opt/alternative/path.d/*"

To disable loading manifests, set the configuration option to an empty list.

manifests:
    kustomizePaths: []

Manifest Example

The example demonstrates automatic deployment of a busybox container using kustomize manifests in the /etc/microshift/manifests directory.

Run the following command to create the manifest files.

MANIFEST_DIR=/etc/microshift/manifests
sudo mkdir -p ${MANIFEST_DIR}

sudo tee ${MANIFEST_DIR}/busybox.yaml &>/dev/null <<EOF
apiVersion: v1
kind: Namespace
metadata:
  name: busybox
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: busybox-deployment
  namespace: busybox
spec:
  selector:
    matchLabels:
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      containers:
      - name: busybox
        image: BUSYBOX_IMAGE
        command:
          - sleep
          - "3600"
EOF

sudo tee ${MANIFEST_DIR}/kustomization.yaml &>/dev/null <<EOF
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

namespace: busybox
resources:
  - busybox.yaml
images:
  - name: BUSYBOX_IMAGE
    newName: busybox:1.35
EOF

Restart the MicroShift service to apply the manifests and verify that the busybox pod is running.

sudo systemctl restart microshift
oc get pods -n busybox

Storage Configuration

MicroShift's included CSI plugin manages LVM LogicalVolumes to provide persistent workload storage. For LVMS configuration, refer to the dedicated documentation.

Opt-Out of LVMS / Snapshotting Components

Users may prevent either the LVMS CSI driver or the CSI Snapshotter, or both, from being deployed. This is done by specifying supported values under .storage node of the MicroShift config in the following ways:

  storage
    driver: **ENUM**
  • Accepted values: "none", "lvms"
  • Empty value or null field defaults to deploying LVMS.
storage
  optionalCsiComponents: **ARRAY**.
  • Expected values are: ['csi-snapshot-controller', 'csi-snapshot-webhook', 'none']. 'none' is mutually exclusive with all other values.
  • Empty array defaults to deploying snapshot-controller and snapshot-webhook.

Automated Uninstallation is Not Supported

Automated uninstallation is not supported because it poses a risk of orphaning provisioned volumes. Without the LVMS CSI driver, the cluster has no knowledge of the underlying storage interface and thus cannot perform provisioning/deprovisioning or mount/unmount operations. Workloads with attached volumes must be manually stopped, and those volumes must then be manually deleted by the user. Once the MicroShift config storage section is specified with supported values, the user may restart MicroShift. They should see that MicroShift does not redeploy the disabled components after restart.

Drop-in configuration directory

In addition to the existing /etc/microshift/config.yaml configuration file there is a /etc/microshift/config.d configuration directory where you can place fragments of configuration.

At runtime, /etc/microshift/config.yaml and .yaml files inside /etc/microshift/config.d are merged together to create one configuration file which overrides the defaults.

Files in /etc/microshift/config.d are sorted lexicographilly. It is recommended to use numerical prefix for easy reasoning about the priority of the fragments.

For example, given following files:

  • /etc/microshift/config.yaml
  • /etc/microshift/config.d/10-subjectAltNames.yaml
  • /etc/microshift/config.d/20-kubelet.yaml

The final user config will be created by using config.yaml as a base, and then overwriting it with 10-subjectAltNames.yaml, and then overwriting it with 20-kubelet.yaml:

20-kubelet.yaml
     ||
     \/
10-subjectAltNames.yaml
     ||
     \/
config.yaml

Some additional rules:

  • Lists are not merged together, they are overwritten. For example: 
    # 10-san.yaml
apiServer:
  subjectAltNames:
    - host1
    - host2

# 20-san.yaml
apiServer:
  subjectAltNames:
    - hostZ

# end result
apiServer:
  subjectAltNames:
    - hostZ
  • Contents of kubelet: configuration are merged together (unless specific field is a list). For example: 
    # 10-kubelet.yaml
kubelet:
  some_setting: True

# 20-kubelet.yaml
kubelet:
  another_setting: True

# end result
kubelet:
  some_setting: True
  another_setting: True