As I’ve mentioned in previous posts, I’m working on build a Kubernetes cluster out of Raspberry Pis. One of my design goals for the cluster is for it to be modular and separate from my home WiFi network.
To do this, I’ve decided to take one of the Pis and make it into a jumpbox for accessing the cluster and a router that grants the cluster Pis access to the internet. Plan is for it to look somewhat like the diagram below, with the Pi Router connected to my regular home router over WiFi and connected to the Pi Cluster’s 8-port switch over ethernet.
I tried following other guides on the internet (particularly ones trying to do the opposite and configure
wlan0 to be a wireless access point) and had some issues. Turns out things change in Raspbian and some configuration options are no longer valid. So my goal with this post is to be less of an exact “step by step” guide and more of a trail of breadcrumbs to provide some general guidance – and help me remember what I did when this Pi inevitably dies.
I assume if you’ve stumbled upon this post that you probably have all the equipment that you need, but I figured it wouldn’t hurt to mention the relevant equipment I used.
- Raspberry Pi 3 Model B+
- C4 Labs “Zebra” Wood Case
- TP-Link 8-port Gigabit Unmanaged Switch
- Silicon Power 32GB Class 10 microSD card (budget-friendly and fast, time will tell if reliable)
- Monoprice SlimRun Cat6 Ethernet Cables (I really like these)
- Miscellaneous other Cat5 and Cat6 ethernet cables
The gigabit switch is probably overkill for this project since the Pis can’t network nearly that fast – could have also done with Cat5 cable all around – but the reviews were good and the prices were right. So now that that’s out of the way, let’s get in to how I transformed this Raspberry Pi and pile of cables into a functioning router for my Pi Kubernetes cluster.
Install Raspbian Linux
You can download the latest version of Raspbian stretch here. I ended up installing full Raspbian on the Pi Router and Raspbian Lite on all of the other clustered Pis. The full Raspbian includes a graphical desktop environment which certainly came in handy for recovery when I broke my
dhcpcd service and
wlan0 interface. 😉
These are the versions of the important bits involved:
pi@porter:~ $ lsb_release -a No LSB modules are available. Distributor ID: Raspbian Description: Raspbian GNU/Linux 9.4 (stretch) Release: 9.4 Codename: stretch pi@porter:~ $ uname -a Linux porter 4.14.50-v7+ #1122 SMP Tue Jun 19 12:26:26 BST 2018 armv7l GNU/Linux pi@porter:~ $ dnsmasq -v Dnsmasq version 2.76 pi@porter:~ $ dhcpcd --version dhcpcd 6.11.5
I used etcher.io to burn the image to my microSD card and added a
ssh file to the root directory of the card to enable ssh with the
After installing, I used plugged the Pi into my TV and used the GUI to connect it to my home WiFi network. I then changed the hostname to be on theme and
pi user’s password to be a little more secure.
Static IP for Pi Router on Home Network
Since I’ll be using this as a jumpbox, I needed a static IP address for it on my home network. I did the following:
- Looked up the MAC address for the
$ ifconfig wlan0
- Logged in to my home router’s admin portal (for me this was at
192.168.1.1) and reserved a static IP address for this MAC address. For my NETGEAR router I followed these instructions and assigned it
Configure Ethernet Interface on Pi Router
Now that the Pi Router was connected to my home network, I was able to
ssh on to it at the address I gave it.
So I initially followed a guide that instructed me to configure a static IP address for
/etc/network/interfaces and this ended up breaking my
dhcpcd daemon. It failed with errors like this:
Job for dhcpcd.service failed because the control process exited with error code. See "systemctl status dhcpcd.service" and "journalctl -xe" for details.
This meant my
wlan0 connection was down and I could no longer
ssh in to the Pi. Luckily, I had installed the desktop environment and was able to salvage things. So I did some digging and found these two posts on the Raspberry Pi forums:
- Rapsberry Pi Forums: Configuring dhcpcd in Raspbian Stretch
- Rapsberry Pi Forums: problems with stretch static ip dhcpcd
They mainly were concerned with the
wlan0 wireless access point use case, but I adapted the information in them for our situation. The secret was to add the following to our
/etc/dhcpcd.conf file. This file configures our dhcp client daemon (more info here). If you’re interested in even more information about
dhcpcd.conf, I recommend reading these Ubuntu docs.
So I added the following to the bottom of the
sudo vim /etc/dhcpcd.conf
interface eth0 static ip_address=10.0.0.1/8 static domain_name_servers=126.96.36.199,188.8.131.52 nolink
This told it to give the
eth0 interface a static IP address of
10.0.0.1/8 on the internal
10.0.0.0 network which the Pis in the Kubernetes cluster will be on. I also added the
nolink option to get it to set up the interface without it necessarily being attached to the cluster.
Next we’ll install dnsmasq to be our DNS/DHCP server for the cluster.
# Install dnsmasq sudo apt install dnsmasq # Move it's default config file for safe-keeping sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.old
I found this sample config file to be very helpful in explaining the options available. This is how I ended up configuring mine:
# Make a new configuration file for dnsmasq sudo vim /etc/dnsmasq.conf
# Our DHCP service will be providing addresses over our eth0 adapter interface=eth0 # We will listen on the static IP address we declared earlier listen-address=10.0.0.1 # My cluster doesn't have that many Pis, but since we'll be using this as # a jumpbox it is nice to give some wiggle-room. # We also declare here that the IP addresses we lease out will be valid for # 12 hours dhcp-range=10.0.0.32,10.0.0.128,12h # Decided to assign static IPs to the kube cluster members # This would make it easier for tunneling, certs, etc. dhcp-host=b8:27:eb:00:00:01,10.0.0.50 dhcp-host=b8:27:eb:00:00:02,10.0.0.51 dhcp-host=b8:27:eb:00:00:03,10.0.0.52 dhcp-host=b8:27:eb:00:00:04,10.0.0.53 dhcp-host=b8:27:eb:00:00:05,10.0.0.54 dhcp-host=b8:27:eb:00:00:06,10.0.0.55 dhcp-host=b8:27:eb:00:00:07,10.0.0.56 # This is where you declare any name-servers. We'll just use Google's server=184.108.40.206 server=220.127.116.11 # Bind dnsmasq to the interfaces it is listening on (eth0) bind-interfaces # Never forward plain names (without a dot or domain part) domain-needed # Never forward addresses in the non-routed address spaces. bogus-priv # Use the hosts file on this machine expand-hosts # Useful for debugging issues # log-queries # log-dhcp
So I intially had issues with getting
dnsmasq to boot up so I found the
log-dhcp options helpful. They log out to
/var/log/syslog by default on Raspbian, but you’ll want to disable them once you get everything working to put less stress on the SD card.
I had some issues getting
dnsmasq to successfully bind to my
eth0 address on boot. Turns out there’s a bit of a race-condition where it will start up before
dhcpcd has finished getting
eth0 ready and fail with an error like this:
-- Unit dnsmasq.service has begun starting up. Jul 01 21:20:56 porter dnsmasq: dnsmasq: syntax check OK. Jul 01 21:20:56 porter dnsmasq: dnsmasq: failed to create listening socket for 192.168.2.1: Cannot assign requested address Jul 01 21:20:56 porter dnsmasq: failed to create listening socket for 10.0.0.1: Cannot assign requested address Jul 01 21:20:56 porter dnsmasq: FAILED to start up Jul 01 21:20:56 porter systemd: dnsmasq.service: Control process exited, code=exited status=2 Jul 01 21:20:56 porter systemd: Failed to start dnsmasq - A lightweight DHCP and caching DNS server.
I ended up drawing inspiration from this Raspberry Pi Forum post and edited the initialization script for
dnsmasq to make it wait a bit for
dhcpcd. Not sure if this is the best way of doing it (doubtful), but other alternative suggestions didn’t work for me. So I modified the beginning of
/etc/init.d/dnsmasq to look like this:
sudo vim /etc/init.d/dnsmasq
#!/bin/sh # Hack to wait until dhcpcd is ready sleep 10 ### BEGIN INIT INFO # Provides: dnsmasq # Required-Start: $network $remote_fs $syslog $dhcpcd # Required-Stop: $network $remote_fs $syslog # Default-Start: 2 3 4 5 # Default-Stop: 0 1 6 # Description: DHCP and DNS server ### END INIT INFO
Notable changes to
/etc/init.d/dnsmasq above were the hacky
sleep 10 and the addition of
$dhcpcd to the “Required-Start” section.
After all of this, it’s time to try rebooting the Pi:
If everything went as planned, you should be able to validate that
dnsmasq is running by doing:
sudo service dnsmasq status
Forward Internet from WiFi (wlan0) to Ethernet (eth0)
I wanted the Pis in my cluster to be able to access the outside internet, so the next step was to set up some internet forwarding!
/etc/sysctl.conf and uncomment the following line:
sudo vim /etc/sysctl.conf
I then added the following
sudo iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE sudo iptables -A FORWARD -i wlan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT sudo iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT
After all this, my
iptables rules looked like the following:
sudo iptables -L -n -v Chain INPUT (policy ACCEPT 1780 packets, 164K bytes) pkts bytes target prot opt in out source destination Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 20 1520 ACCEPT all -- wlan0 eth0 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 20 1520 ACCEPT all -- eth0 wlan0 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT 871 packets, 104K bytes) pkts bytes target prot opt in out source destination
I wanted to make sure these rules survived across reboots, so I installed a package called
sudo apt install iptables-persistent
As part of the installation process it asked me if I wanted to save the current rules to
/etc/iptables/rules.v4 and I said “of course!”
After all of this I did a
sudo reboot again and
sshed in again.
Testing It All Out
After all of this, I plugged the Pi Router into the switch with all of my clustered Pis. I turned the switch on and off again to force them all to try and reacquire a new DHCP lease and then ran the following on the Pi Router to see if any DHCP leases were granted:
Yep, they were all there! Since I added
expand-hosts to the
dnsmasq.conf configuration, I was able to
ssh on to them by hostname like this:
I executed a few
curl commands (e.g.
curl http://example.com) to confirm that they had internet access and everything worked wonderfully! Additionally, from within
blathers I was able to
ssh pi@nook to confirm that the clustered Pis could communicate with each other.
What Didn’t Work
As I mentioned earlier, the editing
/etc/network/interfaces did not work at all for me. My understanding is that it used to work in older versions of Raspbian, but no longer works correctly in Raspbian stretch.
Additionally, I had trouble around
dnsmasq coming up before
10.0.0.1 was available for it to bind to. Adding a sleep to its init script “fixed” this, but it feels hacky. Still on the hunt for a better solution here.
Like I mentioned earlier, these steps worked for me for my particular version of Raspbian stretch and hardware configuration. As I personally found from past guides, these steps may not continue to work. The gist of things should remain the same, however, so with some skilled Binging I’m sure you’ll get your Pi router working as well. Best of luck!