In my specific case, my router leases IPv6 addresses to my VMs running in my server (in premisses) via DHCP and so... I don't need to hardcode or generate any IP configuration. I just need to inform a DNS server about the dynamically generated addresses.
The snippet below (from my cloud-config script) creates /etc/sysctl.conf so that it enables IPv6 on a VM running Centos7. It also creates a shell script which updates the current IPv6 address onto FreeDNS every 15mins, requiring the FQDN and a DDNS key which can be obtained when you setup a AAAA record marked as dynamic.
local fqdn="vm.example.com" local ddnspasswd='obtain-ddns-key-at-dns.he.net' cat > user-data <<EOF # configure IPv6 write_files: - content: | net.ipv6.conf.all.disable_ipv6 = 0 net.ipv6.conf.default.disable_ipv6 = 0 path: /etc/sysctl.conf owner: root:root permissions: 0600 - content: | #!/bin/bash function ddns_update_ipv4 { local fqdn="${fqdn}" local ddnspasswd="${ddnspasswd}" /usr/bin/curl -4 "https://dyn.dns.he.net/nic/update" -d "hostname=\${fqdn}" -d "password=\${ddnspasswd}" >> /dev/null 2>&1 local STATUS=\$? if [[ \$STATUS -ne 0 ]]; then echo "IPv4 DNS update failed, return code: \$STATUS" >> /var/log/ddns.log return 1 fi return 0 } function ddns_update_ipv6 { local fqdn="${fqdn}" local ddnspasswd="${ddnspasswd}" /usr/bin/curl -6 "https://dyn.dns.he.net/nic/update" -d "hostname=\${fqdn}" -d "password=\${ddnspasswd}" >> /dev/null 2>&1 local STATUS=\$? if [[ \$STATUS -ne 0 ]]; then echo "IPv6 DNS update failed, return code: \$STATUS" >> /var/log/ddns.log return 1 fi return 0 } ddns_update_ipv6 path: /sbin/ddns-update owner: root:root permissions: 0500 # Update IPv6 on FreeDNS (http://dns.he.net/) every 15 mins runcmd: - systemctl stop network && systemctl start network - echo "0,15,30,45 * * * * /sbin/ddns-update" | tee -a /etc/crontab - crontab -u root /etc/crontab EOF
