etcDHCP

Ever wondered what was going on with your DHCP leases? Not comfortable looking at /var/lib/dhcp/dhcp.leases? Feel like your DHCP should be a bit higher availablilty, and a little bit more stateless? Prefer GRPC to ARP? Want to make your DHCP server a legitimate microservice? Is dhcpd not cloud native enough for you?

If any of that applies to you, I may have the DHCP server of your dreams, right here. etcDHCP is the worlds first strongly consistent distributed DHCP server (in the absence of any other google results), using CoreOS's etcd to ensure that whatever happens, your leases will remain available. Well, at least, in 49% of cases. Assuming all cases have an independent effect on your etcd nodes.

Install

If you've never built a Go project before, I'm sorry.

$ go get -u github.com/golang/dep/cmd/dep
$ go get github.com/lclarkmichalek/etcdhcp
$ cd $GOPATH/src/github.com/lclarkmichalek/etcdhcp
$ dep ensure
$ go install

Setup

etcd

etcDHCP requires etcd, surprisingly enough. Notably, it requires at least version 3.3.0. However, this version doesn't actually exist yet, so just run master.

etcDHCP

Because running --help is hard, I guess.

$ etcdhcp \
  -etcd.discovery.endpoints localhost:2379 \
  -v=2 \
  -dhcp.router 10.6.9.1 \
  -dhcp.dns 10.6.9.1 \
  -dhcp.server-if wlan0_ap \
  -dhcp.server-ip 10.6.9.1 \
  -dhcp.subnet-mask 255.255.255.0 \
  -dhcp.issue-from 10.6.9.10 \
  -dhcp.issue-to 10.6.9.100 \
I0717 17:39:22.076564   25273 main.go:51] starting dhcp listener
I0717 17:39:22.076564   25273 main.go:45] starting admin server on :9842

There are tons of etcd options, most of which will probably be useless, as if you're not yet running a DHCP server, there's a decent chance that SRV record resolution won't be working. Notably missing is discovery via MAC address. Now that'd be fun..

The DHCP options should be, um, well, let's hope you've configured a DHCP server before. Plenty of things aren't supported, but you can certainly get a lot of stuff working by writing to etcd directly.

Operating concerns

Like all ~~good~~ cloud native software, etcDHCP exports Prometheus metrics on :9842. There's also pprof endpoints exposed. I didn't implement a readiness or liveness endpoint, as um, well they'd be a bit pointless. Also no graceful shutdowns because github.com/krolaw/dhcp4 doesn't support context yet.

etcd structure

$ ./etcdctl get etcdhcp::ips::leased::10.6.9.99
etcdhcp::ips::leased::10.6.9.99
5c:96:56:a4:be:eb
$ ./etcdctl get etcdhcp::ips::free::10.6.9.94
etcdhcp::ips::free::10.6.9.94
10.6.9.94
$ ./etcdctl get etcdhcp::nics::leased::08:9e:08:b5:af:01
etcdhcp::nics::leased::08:9e:08:b5:af:01
10.6.9.97

Want to add more IPs? Either restart the dhcp server with a different range, or..

$ for i in `seq 200 220`; do ./etcdctl put etcdhcp::ips::free::10.6.9.$i 10.6.9.$i; done

Warning: IPs that aren't in the range of a running server will gradually be phased out. They'll be removed when they are picked up by a client, and that client allows the lease to expire.

Want to react to a device connecting? Watch the nic entry for the device's MAC address:

$ etcdctl watch etcdhcp::nics::leased::08:9e:08:b5:af:01

Beware that renewals will cause updates to the nic key (updating/changing the lease to one with a more recent expiry). make sure to watch for creation/deletion events only.

Want to give a specific device a specific ip? Just associate the two, and any DHCP discovery request will pick up the existing association.

$ etcdctl put etcdhcp::nics::leased::08:9e:08:b5:af:01 10.6.9.2
$ etcdctl put etcdhcp::ips::leased::10.6.9.2 08:9e:08:b5:af:01
$ etcdctl delete etcdhcp::ips::free::10.6.9.2

Warning: the leased keys have ttls set when a lease is issued, so you should set this up in a cron or something.