When considering high availability for network services, DHCP is often a critical component. The question arises: how can you achieve DHCP server redundancy, especially when running DHCP in containers? Let’s explore setting up redundant DHCP servers and how containerization plays a role.
One common approach involves leveraging DHCP helper addresses on your network’s Layer 3 devices. These helpers forward DHCP requests to designated DHCP servers. The key to redundancy here is the order in which you specify these server addresses. The network device attempts to contact the first server on the list, and if it’s unavailable, it proceeds to the next. This mechanism allows for a degree of automatic failover.
To ensure seamless operation when a DHCP server fails, each server should be configured to check if an IP address is already in use before assigning a new lease. Fortunately, with dhcpd, this behavior is default. If your primary DHCP server goes down, the secondary server will begin issuing leases. Clients renewing their leases will eventually get new IP configurations from the active server.
While lease table synchronization between DHCP servers via tools like rsync is technically possible, it’s often considered unnecessary for basic redundancy. The disruption is usually minimal as devices retain their IPs until lease renewal. For environments utilizing Dynamic DNS (DDNS), ensure both DHCP servers are configured to update your BIND DNS records correctly. This setup manages DNS entries effectively even during a DHCP server switch.
It’s worth noting that dedicated High Availability (HA) DHCP solutions exist, such as the failover feature in Windows DHCP Server. However, these often operate on an active-active split-scope model (e.g., 80/20 range distribution) rather than a true load-balanced or fully automatic takeover system like you might find with web servers and load balancers. Containerizing your DHCP server doesn’t fundamentally change these redundancy principles, but it offers benefits like easier deployment and management of your DHCP server instances, making the implementation of these redundancy strategies more agile and scalable.
