On the Strato customer service website
create a subdomain like mysub.example.com.
Install the ddclient using the -y option to prevent having questions asked.
apt install -y ddclient
Modify configuration file /etc/ddclient.conf .
# Used protocol at Strato.
protocol=dyndns2
# Use the IP from the web because at AWS your are in a local subnet.
use=web
# Communication to Strato shoud be secured.
ssl=yes
# Server URL to Strato service.
server=dyndns.strato.com/nic/update
# Login should be the domain name at Strato.
login=mysub.example.com
# Password given at Strato for the DynDNS service.
password='strato-dyndns-password'
# Domain it is all about.
mysub.example.com
Modify configuration file /etc/default/ddclient to match as bellow.
# Set to "true" if ddclient should be run every time DHCP client ('dhclient'
# from package isc-dhcp-client) updates the systems IP address.
run_dhclient="true"
# Set to "true" if ddclient should be run every time a new ppp connection is
# established. This might be useful, if you are using dial-on-demand.
run_ipup="false"
# Set to "true" if ddclient should run in daemon mode
# If this is changed to true, run_ipup and run_dhclient must be set to false.
run_daemon="true"
# Set the time interval between the updates of the dynamic DNS name in seconds.
# This option only takes effect if the ddclient runs in daemon mode.
daemon_interval="600"
Test if the configuration succeeded using the command ddclient -daemon=0 -debug -verbose -noquiet.
Check for the last line saying SUCCESS like for example:
SUCCESS: mysub.example.com : skipped: IP address was already set to <the-global-ip>
Check if the daemon is running with command service ddclient status.