Use a custom image to create a Container Service for Kubernetes cluster

Create a Container Service for Kubernetes cluster

We recommend that you first create a dedicated Kubernetes cluster with no worker node or a managed Kubernetes cluster with two worker nodes and then add worker nodes that use a custom image to the cluster. This saves time and decreases the error probability.

1. Create a dedicated Kubernetes cluster with three or five master nodes and no worker node by using a default system image. For more information, see Create a Kubernetes cluster.
   Note If you create a managed Kubernetes cluster, select at least two worker nodes. For more information, see Create a managed Kubernetes cluster.
2. Add worker nodes that use a custom image to the cluster. For more information, see Expand clusters.
   If you want to run an initialization script after you add the worker nodes to the cluster, you can configure the user data for Elastic Compute Service (ECS) instances.

   Note To use custom images and configure the user data, submit a ticket.

The following sections describe how to use ack-image-builder to create a custom image.

Use ack-image-builder

The ack-image-builder tool is developed based on the open-source tool HashiCorp Packer. The ack-image-builder tool provides the default configuration template and verification script for you to create custom images.

With ack-image-builder, you can reduce the error probability caused by manual operations. In addition, the ack-image-builder tool records changes on images to facilitate troubleshooting. To use the ack-image-builder tool to create a custom image for a Container Service for Kubernetes cluster, follow these steps:

1. Install Packer.
   Download Packer from its official website. Make sure that the version is compatible with your operating system. Then, install and verify Packer by following its installation documentation.

   Run the packer version command. If the version number of Packer is returned, Packer is installed successfully.

   $ packer version
   Packer v1.4.1

2. Create a Packer template.
   To use Packer to create a custom image, you must create a template in JSON format. In the template, you must specify the image builder and provisioner that are used to create the custom image. In this example, Alicloud Image Builder and the shell provisioner are used.

   {
     "variables": {
       "region": "cn-hangzhou",
       "image_name": "test_image{{timestamp}}",
       "source_image": "centos_7_06_64_20G_alibase_20190711.vhd",
       "instance_type": "ecs.n1.large",
       "access_key": "{{env `ALICLOUD_ACCESS_KEY`}}",
       "secret_key": "{{env `ALICLOUD_SECRET_KEY`}}"
     },
     "builders": [
       {
         "type": "alicloud-ecs",
         "access_key": "{{user `access_key`}}",
         "secret_key": "{{user `secret_key`}}",
         "region": "{{user `region`}}",
         "image_name": "{{user `image_name`}}",
         "source_image": "{{user `source_image`}}",
         "ssh_username": "root",
         "instance_type": "{{user `instance_type`}}",
         "io_optimized": "true"
       }
     ],
     "provisioners": [
       {
         "type": "shell",
         "scripts": [
           "config/default.sh",
           "scripts/updateDNS.sh",
           "scripts/reboot.sh",
           "scripts/verify.sh"
         ],
         "expect_disconnect": true
       }
     ]
   }

   Parameter	Description
   access_key	Your AccessKey ID.
   secret_key	Your AccessKey secret.
   region	The region of the intermediate instance that is used to create the custom image.
   image_name	The name of the custom image.
   source_image	The name of the source image used to create the custom image. Set this parameter to the name of a public image provided by Alibaba Cloud.
   instance_type	The type of the intermediate instance used to create the custom image.
   provisioners	The provisioner used to create the custom image.

3. Create a Resource Access Management (RAM) user and generate an AccessKey.
   Creating custom images requires high permissions. We recommend that you create a RAM user and use a RAM policy to grant the permissions required by Packer to the RAM user. Then, generate an AccessKey for the RAM user. For more information, see Create an AccessKey.
4. Add the AccessKey information to the template and create a custom image.
   1. Run the following commands to add the AccessKey information:

      export ALICLOUD_ACCESS_KEY=XXXXXX
      export ALICLOUD_SECRET_KEY=XXXXXX

   2. Run the following commands to create a custom image:

      $ packer build alicloud.json
      alicloud-ecs output will be in this color.
      
      ==> alicloud-ecs: Prevalidating source region and copied regions...
      ==> alicloud-ecs: Prevalidating image name...
          alicloud-ecs: Found image ID: centos_7_06_64_20G_alibase_20190711.vhd
      ==> alicloud-ecs: Creating temporary keypair: xxxxxx
      ==> alicloud-ecs: Creating vpc...
          alicloud-ecs: Created vpc: xxxxxx
      ==> alicloud-ecs: Creating vswitch...
          alicloud-ecs: Created vswitch: xxxxxx
      ==> alicloud-ecs: Creating security group...
          alicloud-ecs: Created security group: xxxxxx
      ==> alicloud-ecs: Creating instance...
          alicloud-ecs: Created instance: xxxxxx
      ==> alicloud-ecs: Allocating eip...
          alicloud-ecs: Allocated eip: xxxxxx
          alicloud-ecs: Attach keypair xxxxxx to instance: xxxxxx
      ==> alicloud-ecs: Starting instance: xxxxxx
      ==> alicloud-ecs: Using ssh communicator to connect: 47.111.127.54
      ==> alicloud-ecs: Waiting for SSH to become available...
      ==> alicloud-ecs: Connected to SSH!
      ==> alicloud-ecs: Provisioning with shell script: scripts/verify.sh
          alicloud-ecs: [20190726 11:04:10]: Check if kernel version >= 3.10.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if systemd version >= 219.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if sshd is running and listen on port 22.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if cloud-init is installed.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if wget is installed.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if curl is installed.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if kubeadm is cleaned up.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if kubelet is cleaned up.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if kubectl is cleaned up.  Verify Passed!
          alicloud-ecs: [20190726 11:04:10]: Check if kubernetes-cni is cleaned up.  Verify Passed!
      ==> alicloud-ecs: Stopping instance: xxxxxx
      ==> alicloud-ecs: Waiting instance stopped: xxxxxx
      ==> alicloud-ecs: Creating image: test_image1564110199
          alicloud-ecs: Detach keypair xxxxxx from instance: xxxxxxx
      ==> alicloud-ecs: Cleaning up 'EIP'
      ==> alicloud-ecs: Cleaning up 'instance'
      ==> alicloud-ecs: Cleaning up 'security group'
      ==> alicloud-ecs: Cleaning up 'vSwitch'
      ==> alicloud-ecs: Cleaning up 'VPC'
      ==> alicloud-ecs: Deleting temporary keypair...
      Build 'alicloud-ecs' finished.
      
      ==> Builds finished. The artifacts of successful builds are:
      --> alicloud-ecs: Alicloud images were created:
      
      cn-hangzhou: m-bp1aifbnupnaktj00q7s

      The scripts/verify.sh script is used to verify the custom image.

Use a custom operating system kernel

Container Service for Kubernetes requires a Linux operating system with the kernel of V3.10 or later. We recommend that you only update the RPM packages to be customized. In addition, you must set the boot parameters for the kernel.

$ cat scripts/updateOSKernel.sh
#! /bin/bash
VERSION_KERNEL="3.10.0-1062.4.3.el7"
yum  localinstall -y  http://xxx.xxx.xxx.xxx/kernel-${VERSION_KERNEL}.x86_64.rpm   http://xxx.xxx.xxx.xxx/kernel-devel-${VERSION_KERNEL}.x86_64.rpm   http://xxx.xxx.xxx.xxx/kernel-headers-${VERSION_KERNEL}.x86_64.rpm
grub_num=$(cat /etc/grub2.cfg |awk -F\' '$1=="menuentry " {print i++ " : " $2}' |grep $VERSION_KERNEL |awk -F ':' '{print $1}')
grub2-set-default $grub_num

Customize the operating system kernel

["vm.max_map_count"]="262144"
["kernel.softlockup_panic"]="1"
["kernel.softlockup_all_cpu_backtrace"]="1"
["net.core.somaxconn"]="32768"
["net.core.rmem_max"]="16777216"
["net.core.wmem_max"]="16777216"
["net.ipv4.tcp_wmem"]="4096 12582912 16777216"
["net.ipv4.tcp_rmem"]="4096 12582912 16777216"
["net.ipv4.tcp_max_syn_backlog"]="8096"
["net.ipv4.tcp_slow_start_after_idle"]="0"
["net.core.netdev_max_backlog"]="16384"
["fs.file-max"]="2097152"
["fs.inotify.max_user_instances"]="8192"
["fs.inotify.max_user_watches"]="524288"
["fs.inotify.max_queued_events"]="16384"
["net.ipv4.ip_forward"]="1"
["net.bridge.bridge-nf-call-iptables"]="1"
["fs.may_detach_mounts"]="1"
["net.ipv4.conf.default.rp_filter"]="0"
["net.ipv4.tcp_tw_reuse"]="0"
["net.ipv4.tcp_tw_recycle"]="0"

Use a custom DNS service

Use a custom Yum repository

Preload the container images of DaemonSet components

If you may add more than 1,000 worker nodes to the cluster at a time, we recommend that you preload the container images of DaemonSet components when creating the custom image. This saves the operations for pulling these container images when nodes start and improves the efficiency of cluster scale-outs.

1. Compress the required container images to TAR packages and stores them in the custom image.
   Assume that the Container Service for Kubernetes cluster uses the Terway network plug-in and Container Storage Interface (CSI) storage plug-in and resides in the China (Hangzhou) region. The sample script for preloading the container images of the preceding plug-ins is as follows:

   $ cat scripts/prepare-images.sh
   #! /bin/bash
   set -x -e
   EXPORT_PATH=/preheated
   
   # Install Docker.
   yum install -y docker
   systemctl start docker
   
   # Pull and save images.
   images=(
   registry-vpc.cn-hangzhou.aliyuncs.com/acs/csi-plugin:v1.14.5.60-5318afe-aliyun
   registry-vpc.cn-hangzhou.aliyuncs.com/acs/terway:v1.0.10.78-g97729ee-aliyun
   )
   
   mkdir -p ${EXPORT_PATH}
   
   for image in "${images[@]}"; do
       echo "preheating ${image}"
       docker pull ${image}
       docker save -o ${EXPORT_PATH}/$(echo ${image}| md5sum | cut -f1 -d" ").tar ${image}
   done
   
   # Uninstall Docker.
   yum erase -y docker
   rm -rf /var/lib/docker

2. Log on to the Container Service console. Go to the cluster creation page, click Show Advanced Options, and then enter the following script in the User Data field:

   ls /preheated/ | xargs -n 1 -i docker load -i /preheated/{}
   rm -rf /preheated

Edit the configuration file of the custom image

Add the following configurations about provisioners to the alicloud.json file for creating the custom image:

  "provisioners": [
    {
      "type": "shell",
      "scripts": [
        "config/default.sh",
        "scripts/updateOSKernel.sh",
        "scripts/updateDNS.sh",
        "scripts/add-yum-repo.sh",
        "scripts/prepare-images.sh",
        "scripts/reboot.sh",
        "scripts/verify.sh"
      ],
      "expect_disconnect": true
    }
  ]

After you edit the configuration file of the custom image, you can create the custom image and use it to create or scale out a Container Service for Kubernetes cluster.