This section describes AMIs and instances, the basic building blocks of Amazon EC2. Before accomplishing anything with Amazon EC2, you must understand the concepts in this section.
An Amazon Machine Image (AMI) is an encrypted machine image that contains all information necessary to boot instances of your software. For example, an AMI might contain all the software to act as a web server (e.g., Linux, Apache, and your web site) or it might contain all the software to act as a Hadoop node (e.g., Linux, Hadoop, and a custom application).
You launch one or more instances of an AMI. An instance might be one web server within a web server cluster or one Hadoop node.
An Amazon EC2 instance can be launched from an AMI backed by Amazon S3 or an AMI backed by Amazon EBS. Instances launched from AMIs backed by Amazon S3 use an instance store as the root device (e.g., / or C:\). Instances launched from AMIs backed by Amazon EBS use Amazon EBS volumes as their root devices.
The following table describes the differences between AMIs backed by Amazon S3 and AMIs backed by Amazon EBS.
| Root Device | Instance Store | Amazon EBS |
|---|---|---|
|
Boot Time |
Usually Less than 5 minutes |
Usually Less than 1 minute |
|
Size Limit |
10 GiB |
1 TiB |
|
Location |
Instance storage |
Amazon EBS volume |
|
Data Persistence |
Data persists for the life of the instance; non-root devices can use Amazon EBS |
Data persists on instance failure and can persist on instance termination |
|
Upgrading |
Instance attributes are fixed for the life of an instance |
The kernel, instance type, and ramdisk can be changed while the instance is stopped. |
|
Charges |
Instance usage and AMI storage |
Instance usage, Amazon EBS volume usage, and AMI Storage |
|
AMI Creation |
Requires installation and use of AMI tools |
Uses a single command/call |
|
Stopped State |
Cannot be in stopped state; instances are running or not |
Can be placed in stopped state where instance is not running, but state is maintained in Amazon EBS |
Public AMIs are available from Amazon and the Amazon EC2 community and can be downloaded from the Resource Center. You can use public AMIs as a base to create your own custom private AMIs.
Private AMIs are AMIs that you own and can only be accessed by you or those to whom you grant access.
Shared AMIs are AMIs that developers build and make available for other AWS developers to use. Building safe, secure, useable AMIs for public consumption is a fairly straightforward process, if you follow a few simple guidelines. For information on how to use shared AMIs and how to share AMIs, see Using Shared AMIs and How to Share AMIs.
Paid AMIs are AMIs that you purchase from developers or AMIs that come with service contracts from organization such as Red Hat.
To use a file system image with Amazon EC2, you must prepare and create it as an AMI.
An Amazon EC2 instances can use its instance store (Amazon S3-backed) as its root device or an Amazon EBS volume (Amazon EBS-backed).
The creation process for an AMI that uses an instance store as its root device does the following:
![[Important]](important.png)
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Important |
|---|---|
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After completion, you must register the AMI. |
The creation process for an AMI that uses an Amazon EBS volume as its root device uses one of the following methods:
After an AMI is launched, the resulting running system is called an instance. By default, you can run up to 20 instances. If you need more than 20 instances, please complete the Amazon EC2 Instance Request Form and your request will be considered.
Instances remain running unless they fail or are terminated. When this happens, the data on the instance is no longer available. However, if an instance fails that uses an Amazon EBS volume as its root device, the data remains available.
![[Note]](note.png)
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Note |
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Instances that use Amazon EBS volumes as their root devices can delete their volumes on termination or leave them running. If an instance fails that uses an Amazon EBS volume as its root device, the volume continues running and can be mounted by another instance. |
Amazon EC2 instances are grouped into three families: standard, High-CPU, and High-Memory. Standard instances have memory to CPU ratios suitable for most general purpose applications; High-CPU instances have proportionally more CPU resources than memory (RAM) and are well suited for compute-intensive applications. High-Memory instances have proportionally more memory resources and are well suited for high throughput applications, such as database and memory caching applications.
When selecting instance types, you might want to use less powerful instance types for your web server instances and more powerful instance types for your database instances.
![[Tip]](tip.png)
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Tip |
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One of the advantages of Amazon EC2 is that you pay by the instance hour, which makes it convenient and inexpensive to test the performance of your application on different instance families and types. A good way to determine the most appropriate instance family and instance type is to launch test instances and benchmark your application. |
The instance types described in the following table are available.
| Type | CPU | Memory | Storage | Platform | I/O | Name |
|---|---|---|---|---|---|---|
|
Small |
1 EC2 Compute Unit (1 virtual core with 1 EC2 Compute Unit) |
1.7 GB |
160 GB instance storage (150 GB plus 10 GB root partition) |
32-bit |
Moderate |
m1.small |
|
Large |
4 EC2 Compute Units (2 virtual cores with 2 EC2 Compute Units each) |
7.5 GB |
850 GB instance storage (2 x 420 GB plus 10 GB root partition) |
64-bit |
High |
m1.large |
|
Extra Large |
8 EC2 Compute Units (4 virtual cores with 2 EC2 Compute Units each) |
15 GB |
1690 GB instance storage (4 x 420 GB plus 10 GB root partition) |
64-bit |
High |
m1.xlarge |
|
High-CPU Medium |
5 EC2 Compute Units (2 virtual cores with 2.5 EC2 Compute Units each) |
1.7 GB |
350 GB instance storage (340 GB plus 10 GB root partition) |
32-bit |
Moderate |
c1.medium |
|
High-CPU Extra Large |
20 EC2 Compute Units (8 virtual cores with 2.5 EC2 Compute Units each) |
7 GB |
1,690 GB instance storage (4 x 420 GB plus 10 GB root partition) |
64-bit |
High |
c1.xlarge |
|
High-Memory Double Extra Large |
13 EC2 Compute Units (4 virtual cores with 3.25 EC2 Compute Units each) |
34.2 GB |
850 GB instance storage (1 x 840 GB plus 10 GB root partition) |
64-bit |
High |
m2.2xlarge |
|
High-Memory Quadruple Extra Large |
26 EC2 Compute Units (8 virtual cores with 3.25 EC2 Compute Units each) |
68.4 GB |
1690 GB instance storage (2 x 840 GB plus 10 GB root partition) |
64-bit |
High |
m2.4xlarge |
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Note |
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The small instance type is the original Amazon EC2 instance type
available since the launch of Amazon EC2. It is the default instance type for all customers.
To use other instance types, you must specify them through the |
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Important |
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We strongly recommend using the 2.6.18 Xen stock kernel with High-CPU and High-Memory instances. Although the default Amazon EC2 kernels work, the new kernels provide greater stability and performance for these instance types. For more information about kernels, see Kernels, RAM Disks, and Block Device Mappings FAQ. |
Every instance includes a fixed amount of storage space on which you can store data. Within this document, it is referred to as the "instance store" as it is not designed to be a permanent storage solution.
If an instance reboots (intentionally or unintentionally), the data on the instance store will survive. If the underlying drive fails, the instance is terminated, or the instance is stopped, the data is lost.
If you need a permanent storage solution, we recommend using Amazon EBS. For more information, see Amazon Elastic Block Store.
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Note |
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If you do not use Amazon EBS, make sure to back up important data to Amazon S3. |
Storage is exposed on the instance types as described in the following table.
| Location | Description |
|---|---|
| /dev/sda1 | Formatted and mounted as root (/) on all Linux and UNIX instance types. Formatted and mounted as C:\ on all Windows instance types. |
| /dev/sda2 or xvdb (Windows) | Formatted and mounted as /mnt on m1.small and c1.medium instances. Formatted and mounted on small Windows instance types. |
| /dev/sda3 | Formatted and mounted as /swap on m1.small and c1.medium instances on all Linux and UNIX instance types. Not available on Windows instances. |
| /dev/sdb or xvdb (Windows) | Formatted and mounted as /mnt on m1.large, m1.xlarge, and c1.xlarge Linux and UNIX instances. Formatted and mounted on m1.large, m1.xlarge, and c1.xlarge Windows instances. |
| /dev/sdc or xvdc (Windows) | Available on m1.large, m1.xlarge, and c1.xlarge Linux and UNIX instances. Formatted and mounted on m1.large, m1.xlarge, and c1.xlarge Windows instances. |
| /dev/sdd or xvdd (Windows) | Available on m1.xlarge and c1.xlarge Linux and UNIX instances. Formatted and mounted on m1.xlarge and c1.xlarge Windows instances. |
| /dev/sde or xvde (Windows) | Available on m1.xlarge and c1.xlarge Linux and UNIX instances. Formatted and mounted on m1.xlarge and c1.xlarge Windows instances. |
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Note |
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By default, instance stores are not exposed to Amazon EBS-backed instances. However, they are still available. |
This section describes the differences between standard On-Demand and Reserved Instances.
On-Demand Instances let you pay for compute capacity by the hour with no long-term commitments. This frees you from the costs and complexities of planning, purchasing, and maintaining hardware and transforms what are commonly large fixed costs into much smaller variable costs.
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Note |
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For information about pricing, refer to the Amazon EC2 Product Page. |
With Amazon EC2 Reserved Instances, you can make a low one-time payment for each instance to reserve and receive a significant discount on the hourly usage charge for that instance.
Amazon EC2 Reserved Instances are based on instance type and location (Region and Availability Zone) for a specified period of time (e.g., 1 year or 3 years) and are only available for Linux/UNIX instances.
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Note |
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For information about pricing, refer to the Amazon EC2 Product Page. For information on using Reserved Instances, see Reserving Amazon EC2 Instances. |
This section describes major concepts that you should understand when using Windows instances.
As part of this service, Amazon EC2 instances can now run Microsoft Windows Server 2003 or Microsoft Windows Server 2008. The Windows AMIs provide you with all standard Microsoft Windows Server functionality.
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Note |
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To get started using Windows instances, we recommend using the AWS Management Console. |
Transitioning to a utility computing model changes how developers are trained to think about CPU resources. Instead of purchasing or leasing a particular processor to use for several months or years, you are renting capacity by the hour. Because Amazon EC2 is built on commodity hardware, over time there might be several different types of physical processors underlying different virtual EC2 instances. Our goal is to provide a consistent amount of CPU capacity regardless of the actual underlying hardware.
Amazon EC2 uses a variety of measures to provide each instance with a consistent and predictable amount of CPU capacity. To make it easy for developers to compare CPU capacity between different instance types, we defined an Amazon EC2 Compute Unit.
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Note |
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We use several internal benchmarks and tests to manage the consistency and predictability of the performance of an Amazon EC2 Compute Unit. For more information, go to the Instance page. |
To find out which instance works best for your application, we recommend launching an instance and using your own benchmark application. This helps you determine which instance type works best for your specific use case.