Missing chrony package in Ubuntu Bionic

I am using HashiCorp Packer to build a new AWS AMI. I want to preinstall the NTP client Chrony (it's popular in our organization and it will get config support from people outside our team). But when I use the AMI and do apt-get update apt-get install -y chrony I get Package 'chrony' has no installation candidate with some other interest bits from the packer build log: amazon-ebs: Reading package lists... amazon-ebs: Building dependency tree... amazon-ebs: Reading state information... amazon-ebs: Package chrony is not available, but is referred to by another package. amazon-ebs: This may mean that the package is missing, has been obsoleted, or amazon-ebs: is only available from another source Which is odd, I'm not touching the /etc/apt/sources.list. If I cat it from the packer environment it looks like (edited to remove Ubuntu inline comments): amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic main restricted amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic-updates main restricted amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic universe amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic-updates universe amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic multiverse amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic-updates multiverse amazon-ebs: deb http://us-west-2.ec2.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse amazon-ebs: deb http://security.ubuntu.com/ubuntu bionic-security main restricted amazon-ebs: deb http://security.ubuntu.com/ubuntu bionic-security universe amazon-ebs: deb http://security.ubuntu.com/ubuntu bionic-security multiverse Seems like that should be sufficient to find chrony? I have also confirmed that chrony is in the bionic distro, it has a package page here: https://packages.ubuntu.com/bionic/chrony . Does apt have different rules for resolving dependencies when run from packer?