Ansible playbook to deploy a DHCP server for private networking on Exoscale

On Exoscale, you can attach a private network to your VMs, which comes unmanaged. To ease the communication between your instances on this private link, let's setup a DHCP server answering requests on the private interface for all your VMs using this second network.

We are going to use Ansible to ease the process of deploying one DHCP server and 3 sample virtual machines to validate the setup.

If you're not familiar with Ansible, it's an open source automation tool for your infrastructure as a code. The only language you'll need is YAML to write the configuration files.

Setup

First you have to clone the repository:

$ git clone https://github.com/marcaurele/ansible-exoscale-privnet.git
$ cd ansible-exoscale-privnet

Create a new virtual environment for Python:

# For python 2
$ virtualenv -p <location_of_python_2.7> venv
# For python 3
$ python3 -m venv venv
# Activate the virtual environment
$ . ./venv/bin/activate

Install the requirements for the playbook (ansible (>=2.4), cs, sshpubkeys):

$ pip install -r requirements.txt

In your shell you need to export those 3 variables, as per cs documentation:

• export CLOUDSTACK_ENDPOINT=https://api.exoscale.ch/compute
• export CLOUDSTACK_KEY=<your-api-key>
• export CLOUDSTACK_SECRET=<your-api-secret-key>

Or if you're alread using a .cloudstack.ini file, you only need to export:

• export CLOUDSTACK_REGION=<section_name>

Your API key can be found at https://portal.exoscale.ch/account/profile/api.

Now you are all set to run the playbook. To verify the setup, from your terminal run:

$ cs listZones

You should get a JSON output of the current zones available on Exoscale.

{
  "count": 3, 
  "zone": [
    {
      "allocationstate": "Enabled", 
      "dhcpprovider": "VirtualRouter", 
      "id": "1128bd56-b4d9-4ac6-a7b9-c715b187ce11", 
      "localstorageenabled": true, 
      "name": "ch-gva-2", 
      "networktype": "Basic", 
      "securitygroupsenabled": true, 
      "tags": [], 
      "zonetoken": "ccb0a60c-79c8-3230-ab8b-8bdbe8c45bb7"
    }, 
    {
      "allocationstate": "Enabled", 
      "dhcpprovider": "VirtualRouter", 
      "id": "91e5e9e4-c9ed-4b76-bee4-427004b3baf9", 
      "localstorageenabled": true, 
      "name": "ch-dk-2", 
      "networktype": "Basic", 
      "securitygroupsenabled": true, 
      "tags": [], 
      "zonetoken": "fe63f9cb-ff75-31d3-8c46-3631f7fcd533"
    }, 
    {
      "allocationstate": "Enabled", 
      "dhcpprovider": "VirtualRouter", 
      "id": "4da1b188-dcd6-4ff5-b7fd-bde984055548", 
      "localstorageenabled": true, 
      "name": "at-vie-1", 
      "networktype": "Basic", 
      "securitygroupsenabled": true, 
      "tags": [], 
      "zonetoken": "26d84c22-f66d-377e-93ab-987ef477cab3"
    }
  ]
}

Quick run

I will discuss the playbook setup afterwards. If you're eager to run the playbook and see the result, run:

$ ansible-playbook deploy-privnet-dhcp.yml

If you wish to deploy those virtual machines in another zone/region, for example de-fra-1 you can overwrite the zone variable on the command line:

$ ansible-playbook deploy-privnet-dhcp.yml -e "zone=de-fra-1"

Playbook roles

Common

This role creates an SSH key "privnet" to be used on all virtual machines deployed by this playbook to authenticate, instead of using a password. This new key generated by CloudStack is saved under ~/.ssh/id_rsa_privnet on your local machine.

Infra

This role provisions the VMs on Exoscale, as well as a new SSH key, security groups, and adds the private networking interface to each of them. What you might not see often is the user_data provided for the VM deployment in create_vm.yml which is used to let cloud-init manage the hostname nicely as done when starting a VM from Exsocale portal:

    user_data: |
      #cloud-config
      manage_etc_hosts: true
      fqdn: {{ zone }}-{{ dhcp_name }}

The private networking interface is added through create_private_nic.yml using Ansible cs_instance_nic module:

- name: "dhcp server : add privnet nic"
  local_action:
    module: cs_instance_nic
    network: "{{ private_network }}"
    vm: "{{ zone }}-{{ dhcp_name }}"
    zone: "{{ zone }}"

It can also be directly attached to the VM on the deployment step in create_vm.yml with the networks attribute:

- name: "dhcp server : create"
  local_action:
    module: cs_instance
    name: "{{ zone }}-{{ dhcp_name }}"
    template: "{{ template }}"
    root_disk_size: "{{ root_disk_size }}"
    service_offering: "{{ instance_type }}"
    ssh_key: "{{ ssh_key }}"
    security_groups: [ '{{ security_group_name }}' ]
    networks:
      - "{{ private_network }}"
    user_data: |
      #cloud-config
      manage_etc_hosts: true
      fqdn: {{ zone }}-{{ dhcp_name }}
    zone: "{{ zone }}"

This instructs Ansible to attach a new NIC to VM {{ dhcp_name }} in the {{zone }} zone on the privNetForBasicZone network. A new eth1 interface comes up on your Linux Ubuntu box for the DHCP server to bind to.

DHCP/server

This role configures the DHCP server. We configure a static IP address for its privnet interface eth1 in configure_private_nic.yml and activate the interface:

- name: upload network interface configuration
  template:
    src: privnet.cfg.j2
    dest: /etc/network/interfaces.d/01-privnet.cfg
    force: yes
  register: privnet_cfg

- name: enable privnet interface
  shell: "ifup eth1"
  when: privnet_cfg.changed

In setup_dhcp_server.yml we install ISC DHCP server with a basic configuration to serve IP addresses in the range 10.11.12.2 - 10.11.12.30:

- name: install packages
  apt:
    name:
      - isc-dhcp-server
    state: present

- name: set listening interfaces
  lineinfile:
    path: /etc/default/isc-dhcp-server
    line: "INTERFACES=\"eth1\""
    regexp: "^INTERFACES"
  notify: restart dhcp server

- name: set configuration
  template:
    dest: /etc/dhcp/dhcpd.conf
    src: dhcpd.conf.j2
    owner: root
    group: root
  notify: restart dhcp server

DHCP/client

This role is the simplest through configure_private_nic.yml: it uploads the network interface configuration file for the privnet and enables it:

- name: copy network interface configuration
  copy:
    src: privnet.cfg
    dest: /etc/network/interfaces.d/01-privnet.cfg
    force: yes
  register: privnet_cfg

- name: enable privnet interface
  shell: "ifup eth1"
  when: privnet_cfg.changed

Going further

This setup could be extended to also configure the DHCP server with static DHCP mappings for your VMs based on their private interface MAC address.