I'm trying to share my AMI with a colleague, who is testing his change to my cluster computing application.
While it is easy to change the permission of my AMI to 'public', I can't find its manifest anywhere, including in my S3 buckets.
Is this feature missing for AMI created in EC2 console?
A manifest is only required for an Instance-Store Backed AMI. This is where the AMI is copied to Instance Store (ephemeral storage) rather than an EBS volume. This method is quite old and these days it is recommended to use a normal AMI that is used to create an EBS boot volume.
AMIs created in the EC2 Management Console can be shared either publicly or with with specific accounts.