There were no errors in /var/log/cloud-init-output.log. In fact, when I look at /etc/resolv.config, the changes have been made, but, and the bit I forgot to mention is, the error message "Failed to receive 1 resource signal(s) within the specified duration". Is it possible that certain linux commands don't work well with init-signal in certain situations?

This document describes how to troubleshoot that error when it appears. https://repost.aws/knowledge-center/cloudformation-failed-signal Basically, we recognize that Linux commands can be executed with cloud-init.

ec2.InitCommand.shellCommand('rm -f /etc/securetty'), => file is removed and signal returned to cfn/cdk

ec2.InitCommand.shellCommand('rm -f /etc/resolv.conf') => file is removed and no signal returned to cdk/cfn. As a result, "The following resource(s) failed to create: [myclientami5D1A95132]" was assumed, even though it was up and running before the rollback. Not sure if the troubleshooting doc can help anymore

Are there any errors in logs such as "/var/log/cloud-init.log" and "/var/log/cfn-init.log"?

more /var/log/cloud-init.log | grep resolv

Apr 30 16:06:28 cloud-init[2518]: stages.py[INFO]: Skipping modules ['resolv-conf'] because they are not verified on distro 'amazon'. To run anyway, add them to 'unverified_modules' in config. Apr 30 16:06:28 cloud-init[2518]: stages.py[DEBUG]: Running module resolv-conf (<module 'cloudinit.config.cc_resolv_conf' from '/usr/lib/python2.7/dist-packages/cloudinit/config/cc_resolv_conf.pyc'>) with frequency once-per-instance Apr 30 16:06:28 cloud-init[2518]: util.py[DEBUG]: Writing to /var/lib/cloud/instances/i-0d74593409a869245/sem/config_resolv_conf - wb: [644] 20 bytes Apr 30 16:06:28 cloud-init[2518]: helpers.py[DEBUG]: Running config-resolv-conf using lock (<FileLock using file '/var/lib/cloud/instances/i-0d74593409a869245/sem/config_resolv_conf'>) Apr 30 16:06:28 cloud-init[2518]: cc_resolv_conf.py[DEBUG]: Skipping module named resolv-conf, no 'manage_resolv_conf' key in configuration