One way to deal with changing IP addresses on my raspberry Pi cluster

One of the annoyances I have with my router (it's actually a hotspot) is that every time I start up my Pi cluster, they all have different IP addresses than they had the day before.

So - I have two ways to deal with this.

The first way - I scp the IP addresses as a file (after the pi's start up) to my work computer, then generate an ssh_config file. The second way, I request the same IP from my hotspot. All my Pi's are running Debian Jessie with systemd.

The first way: 

scp (or you could email it) the IP address after networking has started up.

The links:

Running Services After the Network is up
[Solved] SystemD, how to start a service after network is up.

Overview:

To do this with systemd, I had to create the script to scp the ip, make sure it was executable and then copied to /usr/bin/.

Then, I had to create a systemd service file, copy that to /etc/systemd/system/ and enable the service.

The Details:

The script to scp the IP address:

$cat send_ip_address.sh
#! /bin/bash

IP_ADDR=`ifconfig wlan0 | grep 'inet addr:' | cut -f 12 -d ' ' | cut -c 6-`
echo $IP_ADDR > /tmp/$HOSTNAME

scp -i /home/panchod/.ssh/id_rsa -o StrictHostKeyChecking=no /tmp/$HOSTNAME panchod@192.168.0.174:/home/panchod/lan/ip_addresses/

You'll undoubtedly notice -o StrictHostKeyChecking=no. This is to avoid the nastiness of the host not being in the known_hosts file.

The service file:

$ cat send_ip.service
[Unit]
Description=Send ip address to my Toshiba on startup
After=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/bin/send_ip_address.sh

[Install]
WantedBy=multi-user.target
WantedBy=graphical.target

And then I wrote a script to install everything:

$ cat set_up.sh
#! /bin/bash

sudo cp -iv send_ip_address.sh /usr/bin
sudo cp -iv send_ip.service /etc/systemd/system/send_ip.service
sudo systemctl enable send_ip.service

I made set_up.sh executable. Put them all in the same directory. Tar'd and zip'd the directory. Then, just scp'd the tarball to each pi, untar'd the tarball and ran set_up.sh. Done and done. I should have used ansible - but I'm not there yet.

On my work machine - it's kind of kooky how I have it set up, so it's probably not what you'd do. Because I use ssh for work, and therefore can't mess with .ssh/config (because it's shared) I'll tell you what I do instead.

I have an alias set up for my local lan and use a separate config file.

alias lssh='ssh -F ~/lan/ssh_config'

ssh_config looks like this:

$ cat ~/lan/ssh_config
Host localCluster.*
  User root
  Port 22
  IdentityFile /home/panchod/.ssh/id_rsa-new_pi_net


Host localCluster.bpi-iot-ros-ai
  HostName 192.168.0.198
Host localCluster.raspberry-pi-1
  HostName 192.168.0.144
Host localCluster.raspberry-pi-2
  HostName 192.168.0.154
Host localCluster.raspberry-pi-3
  HostName 192.168.0.153
Host localCluster.raspberry-pi-4
  HostName 192.168.0.117
Host localCluster.raspberry-pi-6
  HostName 192.168.0.131

 and I have bash completion set-up for it:

#=====================================================================
#                       LAN SSH Autocomplete
#=====================================================================

_complete_lssh_hosts()
{
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    comp_lssh_hosts=`cat ~/lan/ssh_config| \
        grep "^Host " | \
        awk '{print $2}' | grep -v "\*"
        `
    COMPREPLY=( $(compgen -W "${comp_lssh_hosts}" -- $cur) )
    return 0
}
complete -F _complete_lssh_hosts lssh

So - when I type lssh <tab> it starts off with localCluster. I can then hit <r><tab> for raspberry-pi and it fills in the rest, then just pick which one I want.

I also had to make a script to generate the ssh_config file. This is a little more complicated than it needs to be, but there was a reason I did it this way.

First - I have all the pi stuff in ~/lan/. As you can see above - the IP addresses are in ~/lan/ip_addresses. I put the header of ssh_config in ~/lan and called it ssh_config_preface.txt. It looks like this:

 Host localCluster.*
  User root
  Port 22
  IdentityFile /home/panchod/.ssh/id_rsa-new_pi_net

The script to generate the config that you see above:
$cat set_up_ssh.sh

#! /bin/bash

BASE_DIR=/home/panchod/lan
SSH_FILE=$BASE_DIR/ssh_config
CLUSTER_FILE=$BASE_DIR/cluster

cat /home/panchod/lan/ssh_config_preface.txt > $SSH_FILE

if grep localCluster $CLUSTER_FILE ;
    then
    echo "Cluster exists in $CLUSTER_FILE - replacing it"
    sed -i 's/localCluster.*/localCluster    /g' $CLUSTER_FILE
else
    echo "Cluster doesn't exists creating it"
    echo "localCluster        " >> $CLUSTER_FILE
fi

for i in /home/panchod/lan/ip_addresses/* ; do

    NAME=`basename $i`
    #echo $NAME
    IP=`cat $i`
    #echo $IP

    echo "Host localCluster.$NAME
    HostName $IP" >> $SSH_FILE
     sed -i "s/^localCluster.*$/& $IP/g" $CLUSTER_FILE
done

echo $SSH_FILE
cat $SSH_FILE
echo; echo
echo $CLUSTER_FILE
cat $CLUSTER_FILE

I also use cssh, so I have an alias for that as well: alias lcssh='cssh -c /home/panchod/lan/cluster'.

I should add a test to ensure that the files exist, but this isn't production, and I only wrote them for me, so if they fail - no one to blame but myself.

[Edit: changed the location of .ssh_config for consistency]