examples.md

Examples

Here you can find a bunch of simple examples for using ct, with some explanations about what they do. The examples here are in no way comprehensive, for a full list of all the options present in ct check out the configuration specification.

Users and groups

passwd:
  users:
    - name: core
      password_hash: "$6$43y3tkl..."
      ssh_authorized_keys:
        - key1

This example modifies the existing core user, giving it a known password hash (this will enable login via password), and setting its ssh key.

passwd:
  users:
    - name: user1
      password_hash: "$6$43y3tkl..."
      ssh_authorized_keys:
        - key1
        - key2
    - name: user2
      ssh_authorized_keys:
        - key3

This example will create two users, user1 and user2. The first user has a password set and two ssh public keys authorized to log in as the user. The second user doesn't have a password set (so log in via password will be disabled), but have one ssh key.

passwd:
  users:
    - name: user1
      password_hash: "$6$43y3tkl..."
      ssh_authorized_keys:
        - key1
      home_dir: /home/user1
      no_create_home: true
      groups:
        - wheel
        - plugdev
      shell: /bin/bash

This example creates one user, user1, with the password hash $6$43y3tkl..., and sets up one ssh public key for the user. The user is also given the home directory /home/user1, but it's not created, the user is added to the wheel and plugdev groups, and the user's shell is set to /bin/bash.

Generating a password hash

If you choose to use a password instead of an SSH key, generating a safe hash is extremely important to the security of your system. Simplified hashes like md5crypt are trivial to crack on modern GPU hardware. Here are a few ways to generate secure hashes:

# On Debian/Ubuntu (via the package "whois")
mkpasswd --method=SHA-512 --rounds=4096

# OpenSSL (note: this will only make md5crypt.  While better than plantext it should not be considered fully secure)
openssl passwd -1

# Python
python -c "import crypt,random,string; print(crypt.crypt(input('clear-text password: '), '\$6\$' + ''.join([random.choice(string.ascii_letters + string.digits) for _ in range(16)])))"

# Perl (change password and salt values)
perl -e 'print crypt("password","\$6\$SALT\$") . "\n"'

Using a higher number of rounds will help create more secure passwords, but given enough time, password hashes can be reversed. On most RPM based distributions there is a tool called mkpasswd available in the expect package, but this does not handle "rounds" nor advanced hashing algorithms.

Storage and files

Files

storage:
  files:
    - path: /opt/file1
      filesystem: root
      contents:
        inline: Hello, world!
      mode: 0644
      user:
        id: 500
      group:
        id: 501

This example creates a file at /opt/file with the contents Hello, world!, permissions 0644 (so readable and writable by the owner, and only readable by everyone else), and the file is owned by user uid 500 and gid 501.

storage:
  files:
    - path: /opt/file2
      filesystem: root
      contents:
        remote:
          url: http://example.com/file2
          compression: gzip
          verification:
            hash:
              function: sha512
              sum: 4ee6a9d20cc0e6c7ee187daffa6822bdef7f4cebe109eff44b235f97e45dc3d7a5bb932efc841192e46618f48a6f4f5bc0d15fd74b1038abf46bf4b4fd409f2e
      mode: 0644

This example fetches a gzip-compressed file from http://example.com/file2, makes sure that it matches the provided sha512 hash, and writes it to /opt/file2.

Filesystems

storage:
  filesystems:
    - name: filesystem1
      mount:
        device: /dev/disk/by-partlabel/ROOT
        format: btrfs
        wipe_filesystem: true
        label: ROOT

This example formats the root filesystem to be btrfs, and names it filesystem1 (primarily for use in the files section).

systemd units

systemd:
  units:
    - name: etcd-member.service
      dropins:
        - name: conf1.conf
          contents: |
            [Service]
            Environment="ETCD_NAME=infra0"

This example adds a drop-in for the etcd-member unit, setting the name for etcd to infra0 with an environment variable. More information on systemd dropins can be found in the docs.

systemd:
  units:
    - name: hello.service
      enabled: true
      contents: |
        [Unit]
        Description=A hello world unit!

        [Service]
        Type=oneshot
        ExecStart=/usr/bin/echo "Hello, World!"

        [Install]
        WantedBy=multi-user.target

This example creates a new systemd unit called hello.service, enables it so it will run on boot, and defines the contents to simply echo "Hello, World!".

networkd units

networkd:
  units:
    - name: static.network
      contents: |
        [Match]
        Name=enp2s0

        [Network]
        Address=192.168.0.15/24
        Gateway=192.168.0.1

This example creates a networkd unit to set the IP address on the enp2s0 interface to the static address 192.168.0.15/24, and sets an appropriate gateway. More information on networkd units in CoreOS can be found in the docs.

etcd

etcd:
  version:                     "3.0.15"
  name:                        "{HOSTNAME}"
  advertise_client_urls:       "http://{PRIVATE_IPV4}:2379"
  initial_advertise_peer_urls: "http://{PRIVATE_IPV4}:2380"
  listen_client_urls:          "http://0.0.0.0:2379"
  listen_peer_urls:            "http://{PRIVATE_IPV4}:2380"
  initial_cluster:             "{HOSTNAME}=http://{PRIVATE_IPV4}:2380"

This example will create a dropin for the etcd-member systemd unit, configuring it to use the specified version and adding all the specified options. This will also enable the etcd-member unit.

This is referencing dynamic data that isn't known until an instance is booted. For more information on how this works, please take a look at the referencing dynamic data document.

Updates and Locksmithd

update:
  group:  "beta"
locksmith:
  reboot_strategy: "etcd-lock"
  window_start:    "Sun 1:00"
  window_length:   "2h"

This example configures the Container Linux instance to be a member of the beta group, configures locksmithd to acquire a lock in etcd before rebooting for an update, and only allows reboots during a 2 hour window starting at 1 AM on Sundays.