rancher-agent registration with terraform on coreos container linux

container-config.tpl

storage:
  files:
    - filesystem: "root"
      path:       "/etc/hostname"
      mode:       0644
      contents:
        inline: ${hostname}
    - filesystem: "root"
      path:       "/etc/hosts"
      mode:       0644
      contents:
        inline:  "127.0.0.1 ${hostname} localhost\n
                 ::1 ${hostname} localhost"
    - filesystem: "root"
      path:       "/opt/rancher/rancher.sh"
      mode:       0755
      contents:
        inline: |
          #!/bin/sh
          set -e
          umask 077
          ${registration_command}


passwd:
  users:
    - name: core
      ssh_authorized_keys:
        - some key

systemd:
  units:
    - name: register-rancher-agent.service
      enabled: true
      mask: false
      contents: |
        [Unit]
        Description=Setup rancher agent

        [Service]
        Type=oneshot
        ExecStart=/opt/rancher/rancher.sh
        RemainAfterExit=true

        [Install]
        WantedBy=multi-user.target

rancher.jsonnet

function (rancher) {
  provider: {
    rancher: {
      api_url: rancher.api_url,
      access_key: rancher.access_key,
      secret_key: rancher.secret_key
    }
  },
  resource: {
    rancher_environment: {
      target_environment: {
        name: rancher.environment,
        orchestration: "cattle"
      }
    },
    rancher_registration_token: {
      registration_token: {
        count: "${local.count}",
        environment_id: "${rancher_environment.target_environment.id}",
        name: "registration_token",
        description: "Host registration token for specified environment"
      }
    },
    data: {
      template_file: {
        container_config: {
          count: "${local.count}",
          template: '${file("./templates/rancher_agents/container-config.tpl")}',
          vars: {
            hostname: "${lookup(local.hosts, count.index)}",
            registration_command: "${element(rancher_registration_token.registration_token.*.command, count.index)}"
          }
        }
      }
    }
  }
}

For those who are new to jsonnet, you can convert the above to json. Just hard code your rancher info (keys/url).