Understanding Amazon AMI

Amazon Machine Image or AMI is a preconfigured operating system with virtual application software that is used to create a virtual machine within the Amazon Web Services’ AWS EC2.

An Amazon AMI is the basic unit of deployment for the various services delivered via the Elastic Compute Cloud. Users of AWS can easily find an available EC2 AMI, but in certain conditions it may be difficult to find an AMI that meets the particular requirements of the user. Also in many cases the available images may be bloated or provide too much customization, perform poorly or lack any type of reasonable documentation. Several security concerns are also associated with some third party AMIs. In such situations users can create their own AMIs containing their applications, data and associated configuration settings.

Creating Own AMI

The AWS provides users an option of creating their own AMI which ensures a better performance besides providing better control over security and reproducibility.  One can easily create his/her own instance store backed and EBS backed Amazon AMI Centos) or Amazon AMI Linux with its own kernel. An AMI does not include a kernel image but only a pointer to the default kernel id which can be chosen from an approved list of safe kernels. This list is maintained by Amazon and its partners. Amazon AMI pricing calls for including the cost of instance storage in the instance cost itself. However, if you use EBS volumes, you will be billed for the total amount of storage you provision. Snapshots are billed depending on how much data is included in it.

The Amazon AMIs are preconfigured with several operating systems LINUX,  Windows, Ubuntu, Debian, Gentoo, Fedora. The AMI works as the basic unit of deployment by allowing them to rapidly boot new custom instances as and when needed. The users can also choose an existing AMI and modify it to suit their own individual needs. The main component of an AMI is a read only file image which includes an operating system which could be Linux, UNIX or Windows and any other additional software required to deliver a service or portion of it.  Amazon EC2 instance store-backed AMIs are limited to 10 GB storage for the root device whereas Amazon EBS (Elastic Load Balancing) backed AMIs are limited to 1 TB. All information about the AMI including its name, version, architecture, default kernel id, decryption key and digests for all the file system chunks are stored in an XML manifest file.

The AMI settings allow the user to share it with another AWS account holder or with public or keep it private. In case you are sharing an AMI with public, you should remove all sensitive data or software. Before creating an AMI, you should delete the shell history as it may contain some private information like the secret access key. One should also delete the private credentials for third party applications and remote services that may have been stored locally.

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