ISC DHCP server deployment with Ansible

Over the last few weeks I built a new home lab based on the Supermicro A1SAi–2750F motherboard. Instead of manually configuring the required infrastructure services like DNS, NTP, OpenVPN and DHCP, I’m using Ansible to do all of it, in an easy and repeatable fashion. As a reminder Ansible is a YAML based configuration management tool, it’s agentless, use SSH as a communication medium. It’s simple and efficient. Read our intro article for more details. In this article I’ll details how to install a ISC DHCP server using Ansible. ISC DHCP is production-grade software that offers a complete solution for implementing DHCP servers, relay agents, and clients for small local networks to large enterprises.

Requirements

On your management node, you’ll need Python 2.7, Ansible and it’s dependencies (paramiko, PyYAML, jinja2, httplib2). The target node, where we’ll install the DHCP server, should be installed with a barebone Ubuntu 14.04 but any Debian based distribution should work too.

DepOps ISC DHCP Role

When I said Ansible is efficient, I mean it. Just run the following command from your management node to get a DebOps Playbook for DHCPd :

# ansible-galaxy install debops.dhcpd

Ansible Galaxy offers hundreds of reusable Roles for Ansible.

By the way, DebOps team is offering lots of Ansible Playbook to the community. I’m grateful to the DepOps team. For example they offer Roles to Install and Configure :

Java, Golang, NodeJS, PHP, Ruby
ElasticSearch, Redis, Mysql, Postgresql
GitLab
LXC, KVM, OpenVZ
nginx
iptables, SSHd, NFS, Samba, NTP, Rsyslog
and many more stuff.

Variables

Before applying the Playbook to your target node, you need to tune it to your need by using a YAML variable file, vars-dhcpd.yml, mine look like this :

---

dhcpd_authoritative: True
dhcpd_interfaces: [ eth0 ]
ansible_domain: bulb.int

# where to ask for DNS Server / dhcpd_dns_servers
ansible_default_ipv4.address: 192.168.2.1

dhcpd_shared_networks:
  - name: 'ls-bulb-net'
    comment: "Remote shared network"
    subnets: '{{ dhcpd_subnets_local }}'
    options: |
      default-lease-time 600;
      max-lease-time 900;

dhcpd_subnets_local:
 - subnet: '192.168.2.0'
   netmask: '255.255.255.0'
   routers: [ '192.168.2.1' ]
   pools:
     - comment: "ls-web pool"
       range: '192.168.2.100 192.168.2.199'

 - subnet: '192.168.3.0'
   netmask: '255.255.255.0'
   routers: '192.168.3.1'
   options: |
     default-lease-time 300;
     max-lease-time 7200;
   pools:
     - comment: "ls-db pool"
       range: '192.168.3.100 192.168.3.199'

Consult the dhcpd server documentation to get a better understanding of the overall configuration parameters to update this file according to your needs.

dhcpd_authoritative authoritative servers respond with DHCPNAK when getting requests for address he knows nothing about. Otherwise he will remain silent.
dhcpd_shared_networks inform the DHCP server that some IP subnets actually share the same physical network.
subnet required for every subnet which will be served, and for every subnet to which the dhcp server is connected. If a range section is present, it will enable your server to serve addresses.
pools The pool declaration can be used to specify a pool of addresses that will be treated differently than another pool of addresses, even on the same network segment or subnet.

Playbook

To apply the debops.dhcpd role to your target node. Just create a Playbook named infra.yml

---
# This playbook just apply debops.dhcpd Role to a target node. 
- name: Infrastructure Services [DHCP server]
  hosts: target-node

  vars_files:
    - vars-dhcpd.yml

  roles:
     - debops.dhcpd

Inventory

To allow Ansible to connect to your target-node, update your /etc/ansible/hosts inventory file

[target-node]
<IP ADDRESS>

This node should be SSH accessible as root or you’ll have to specify the user and/or private key to use

[target-node]
<IP ADDRESS> ansible_ssh_user=<USERNAME> ansible_ssh_private_key_file=<PRIVATE KEY PATH>

Note: It’s not recommended to put variables in your inventory file, to better comply with Ansible best practice place this in a filename named after your node name (target-node here) in the /etc/ansible/host_vars/ directory. If you always use the same username/private key pair, you can also edit /etc/ansible/ansible.cfg to update the corresponding variables remote_user and private_key_file.

Run the Playbook

You are now ready to run your Ansible Playbook :

# ansible-playbook infra.yml

You should now have a fully operational DHCP server.

Summary

We’ve seen how easy Ansible allows us to configure Infrastructure services like a DHCP server.

It’s done in 4 easy steps :

install an Ansible Galaxy Role
Tune the Role to your need by default value in a YAML variable file
Create a Playbook to apply the role and your variable file to your target node
Run the Playbook

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