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TCR Hosts Updater

Last updated: 2024-12-19 20:02:52

    Overview

    TCR Hosts Updater, a component of TCR Addon, helps you deploy the hosts file on K8s cluster worker nodes in regions without VPC DNS service.

    How It Works

    Hosts Updater mounts a specific ConfigMaps in the K8s cluster as the Volume of a worker node, watches the changes of the config file via inotify (inode notify) of Linux OS, and updates the /etc/hosts file of the worker node accordingly. As we need to edit the /etc/hosts file of the worker node, Daemonset workload is usually used for deployment, and it should be run on each node that you need to update hosts. To allow the DaemonSet workload runs on nodes in the cluster as many as possible, the following tolerations are set in the YAML file of the DaemonSet:
    tolerations:
    - key: node-role.kubernetes.io/master
    effect: NoSchedule
    - key: node.kubernetes.io/disk-pressure
    effect: NoSchedule
    - key: node.kubernetes.io/memory-pressure
    effect: NoSchedule
    - key: node.kubernetes.io/network-unavailable
    effect: NoSchedule
    - key: node.kubernetes.io/not-ready
    effect: NoExecute
    - key: node.kubernetes.io/pid-pressure
    effect: NoSchedule
    - key: node.kubernetes.io/unreachable
    effect: NoExecute
    - key: node.kubernetes.io/unschedulable
    effect: NoSchedule

    Deployment and Usage

    Before the deployment, please create a ConfigMaps resource named updater-config under Namespace of Host Updater (e.g. kube-system), and then create DaemonSet.
    To add or delete entries in hosts, simply edit the updater-config. See below for examples:
    apiVersion: v1
    kind: ConfigMap
    metadata:
    name: updater-config
    namespace: kube-system
    data:
    hosts.yaml: |
    - domain: demo.tencentcloudcr.com
    ip: 10.0.0.2
    disabled: false
    - domain: vpc-demo.tencentcloudcr.com
    ip: 10.0.0.2
    disabled: false
    Note:
    As K8s ConfigMaps Volume is used, after the modification of updater-config, the effective time of the hosts update depends on the sync period of worker node kubelet (default to 1 min) and the Cache TTL of ConfigMaps (default to 1 min). For details, see Mounted ConfigMaps are updated automatically.
    
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