dhcp-server-pb

An Ansible playbook to create an LDAP backed DHCP server

HISTORY

A decade ago I wrote a blog post about how to create an ISC DHCP server backed by an OpenLDAP database. The goal was to allow the DHCP lease reservations to be managed just by modifying the database. For normal use, DHCP host records change rarely and are almost always added rather than removed or modified. In a lab space, especially when using DHCP to initate PXE network boot and OS installation, the hosts may cycle through much more quickly, and asking lab users to manually edit the DHCP server configuration file is undesirable. The ISC DHCP server is able to pull its configuration from an LDAP server and offers a way to create a more user-friendly update method using either a web or CLI interface.

I recently revisited that post and I found that a couple of small things had changed and some new options have appeared since then.

The simple change was that I had to look harder to find the LDAP DHCP schema file in the available packages and convert it to LDIF format. It's still in the ISC Github repository, but it's not always included in the DHCP server packages.

One new option was Ansible, which, while it existed in 2014, it wasn't yet widely used, since its release in Feb 2012. The other is software containers. Again they weren't yet widely used. The final change will completely obsolete this exercise; ISC has deprecated ISC DHCP in favor of ISC Kea. Kea comes native with the ability to manage the configuration from either MariaDB (aka MySQL) or PostgreSQL.

In this repo I make use of Ansible, but so far remain with ISC DHCP and OpenLDAP slapd. I have created an ISC DHCP server container, but I haven't containerized OpenLDAP yet and given the move to ISC Kea and a relational database, I probably won't go much farther in this direction.

The original post used Red Hat Enterprise Linux or Fedora Linux as the OS base. The current version is built using Ubuntu, though the hooks exist to implement it on RPM based systems as well.

Usage

The DHCP server with its attached LDAP server are deployed using the ansible playbook dhcp-server-pb.yaml.

ansible-playbook --vault-secrets-file vault-secrets dhcp-server-pb.yaml

Preparation

git clone https://github.com/markllama/dhcp-server-pb
cd dhcp-server-pb

Host Initialization

I am starting currently with a minimal installation of Ubuntu Server. I have installed it from USB live installer and set a static IP address. I created a non-root user, granted that user sudo access with NOPASSWD and installed an SSH public key. With this, I can configure logins from my deployment system using SSH to a user with sudo privileges to execute the Ansible commands.

• Ubuntu Server
  • Minimal Installation
  • Fixed IP Address
  • SSH server installed
• Local user
  • SSH Public key in .ssh/authorized_keys
  • sudo access with NOPASSWD

Ansible Setup

On the deployment server,

Host Variables

Managing Secrets - Ansible Vault

Execution

Implementation

TODO

• Adapt to RPM based systems
• Convert to use software containers
• Re-implement with ISC Kea and MariaDB

References

• ISC DHCP - https://www.isc.org/dhcp/

• OpenLDAP slapd - https://www.openldap.org/

• ISC Kea - https://www.isc.org/kea/

• MariaDB - https://mariadb.com/