Amazon Web Services (AWS) comprise a public cloud, a collection of computing services that allows one to build and run software services in Amazon's data centers. Fedora publishes system images for AWS's virtual machine platform, Amazon Elastic Compute Cloud (EC2), which allows one to create virtual machines in the cloud with very little effort. The objective of this primer is to familiarize the reader with EC2's terminology and functionality. For more detailed documentation, see the AWS website. For help with Fedora on EC2, ask the Fedora Cloud SIG.
What follows are some short explanations of EC2 terminology. For more detailed information, see the EC2 documentation.
Images and Instances
A machine image is a snapshot of a system (specifically its
/ filesystem) that provides the basis for a virtual machine in EC2. When you run a new virtual machine in EC2 you choose a machine image to use as a template. The new virtual machine is then an instance of that machine image that contains its own copy of everything in the image. The instance keeps running until you stop or terminate it, or until it fails. If an instance fails, you can launch a new one from the same image. You can create multiple instances of a single machine image. Each instance will be independent of the others.
You can use a single image or multiple images, depending on your needs. From a single image, you can launch different types of instances. An instance type defines what hardware the instance has, including the amount of memory, disk space, and CPU power.
Amazon, Fedora, other groups, and individuals publish images for public use. You might only need to use images that reputable sources provide, and you can simply customize the resulting instances to suit your needs as you launch them. You can also create your own machine images, but that is beyond the scope of this document.
Machine images in EC2 are sometimes referred to as AMIs.
Machine images have identifiers that begin with
ami, such as
ami-6ebe4507. Instances have identifiers that begin with the letter
i, such as
Regions and Availability Zones
Amazon hosts datacenters many parts of the world. Those from a particular part of the world make up a region. Regions' names are based on their locations, such as in
Regions are broken up into availability zones, which are designed to isolate failures from one another but still provide faster communication than communication between regions. Distributing a web application amongst several availability zones can help improve its reliability if an availability zone encounters problems. Availability zones' names are based on the regions in which they reside, such as
EC2 instances use one or more of three types of storage provided by AWS:
Amazon Simple Storage Service (S3) is a web service-based storage system that is accessible inside EC2 and elsewhere on the Internet. As this primer will not focus on S3, see the Amazon S3 documentation for more details.
Elastic Block Store (EBS)
Amazon Elastic Block Store (EBS) provides instances with persistent, disk-like storage that you can attach to and detach from instances, similar to portable disk drives. By creating EBS volumes and attaching them to instances you can store data that you wish to be portable to more than one instance in the event an instance fails or is replaced. Since instances' root filesystem tend to have limited space, volumes also provide a simple way of adding additional disk capacity to instances.
Volumes have identifiers that begin with
vol, such as
You can create a backup snapshot of a volume. From the snapshot you can then create a new volume and attach it to another instance. You can create multiple volumes from the same snapshot. Each volume will be independent of the others.
Snapshots have identifiers that begin with
snap, such as
Some instance types have instance storage, scratch space that persists only as long as an instance runs. Instance storage is destroyed when an instance stops, terminates, or fails. For this reason, it is also referred to as ephemeral storage.
When EC2 was first introduced, all machine images were backed by instance storage, meaning that their instances' root filesystems were stored in instance storage. Machine images can now also be backed by EBS, meaning that their instances' root filesystem instead reside on EBS volumes.
A security group defines firewall rules for your instances. These rules specify which incoming network traffic should be delivered to an instance (e.g., accept web traffic on port 80 or SSH traffic on port 22). All other traffic is ignored. By default, a security group has no rules, which causes it to block all incoming traffic. You can modify the rules for a group at any time.
Every instance runs inside of a security group. You can create your own security groups, or you can use the
default security group that EC2 provides for you. When you run a new instance it will run in the
default security group unless you choose a different one.
Getting Started with Fedora on EC2
Get Your Account Details
To use AWS you need to create an online account. You can do this by going to the AWS web site, clicking on Create an AWS Account, and following the instructions.
One can interact with EC2 through either a web-based management console or via euca2ools, a suite of command line tools designed for services like EC2. This tutorial will focus on using EC2 with euca2ools at the command line.
To using the command line tools you first need to obtain access keys for your account. You can find them by going to the AWS management console on the web, clicking your name on the top, followed by
Security Credentials, and scrolling down to the section titled Access Credentials. Make note of the Access Key ID and the Secret Access Key that appears beside it. Both of them should be long sets of alphanumeric characters. Create a file called
.iamrc in your home directory that contains those keys in this format:
Since euca2ools is designed to work with all AWS-compatible clouds, not just AWS itself, it needs to know which cloud to contact. Create a file called
.eucarc in your home directory with the following content to point it toward AWS:
export AWS_CREDENTIAL_FILE=~/.iamrc export EC2_URL=https://ec2.amazonaws.com/ export S3_URL=https://s3.amazonaws.com/ export EUARE_URL=https://iam.amazonaws.com/ source "$AWS_CREDENTIAL_FILE" export EC2_ACCESS_KEY=$AWSAccessKeyId export EC2_SECRET_KEY=$AWSSecretKey export AWS_ACCESS_KEY=$AWSAccessKeyId export AWS_SECRET_ACCESS_KEY=$AWSSecretKeyFinally, add these settings to your shell's environment by running:
Do Initial Setup
Install the Command Line ToolsInstall the euca2ools package. To do so with yum, run:
yum install euca2ools
Choose a Region
Choose an EC2 region to use. Things to consider when choosing a region include its geographic location, the pricing for instances in that region, and whether the image you wish to use is available in that region. You can get a list of regions by running
euca-describe-regions, which results in a list such as this:
REGION eu-west-1 ec2.eu-west-1.amazonaws.com REGION us-east-1 ec2.us-east-1.amazonaws.com REGION ap-northeast-1 ec2.ap-northeast-1.amazonaws.com REGION us-west-1 ec2.us-west-1.amazonaws.com REGION ap-southeast-1 ec2.ap-southeast-1.amazonaws.comWhen you choose an EC2 region you can make euca2ools start using it by editing the line that contains
export EC2_URL=https://ec2.us-east-1.amazonaws.com/...and then re-set the settings in your shell's environment:
Create a Key Pair
The primary way of logging into Fedora instances is via SSH. Since Fedora instances have no passwords, you need a SSH key pair to log in to them. The private half of this key pair is stored on your computer, while the public half is stored in EC2 so instances can download them as they start. This allows you to securely log into your instances without a password.
You can have multiple key pairs. Each key pair has its own name. Key pairs are specific to each EC2 region.Choose a name for a new key pair and then use the
euca-add-keypaircommand to create it and write the private key to a file. Be sure to choose a name that is easy to remember.
euca-add-keypair mykey > mykey.pem
You can use
euca-describe-keypairs to display a list of your keypairs.
$ euca-describe-keypairs KEYPAIR mykey1 7b:9b:33:cf:bf:12:4d:62:b6:7c:fa:02:f2:f7:bc:59:e3:7e:40:fb KEYPAIR mykey2 f9:93:1e:73:4b:2e:c1:0d:7f:79:e1:bc:c0:d0:7c:95:32:55:b7:ddYou can use
euca-delete-keypairsto delete a keypair. Deleting a keypair does not remove it from instances that are already running; it merely prevents new instances from using it.
Set up a Security Group
Each security group has its own set of firewall rules. While this tutorial uses the
default security group that EC2 provides for you, you can also create your own security groups.
euca-authorizecommand lets you tell EC2 to allow traffic from ranges of IP addresses and ports into a security group. To allow access to SSH (TCP port 22) running on instances in the
defaultsecurity group, run the following command:
euca-authorize default -p 22 -s your_system's_ip_address/32If you do not specify a range of IP addresses then the port(s) you choose will be open to the entire Internet. For example, the following command allows SSH access from any machine Internet, not just your computer:
euca-authorize default -p 22To allow pings and other ICMP traffic you can run:
euca-authorize default -P icmp
The opposite of
euca-revoke. You can use
euca-describe-groups to obtain a list of security groups and the firewall permissions you have applied to them.
Run an Instance
You are now ready to run an instance.
Choose an Image
The Cloud SIG maintains an index of machine images published by Fedora. While all of the images for a given release behave the same, they differ by architecture, EC2 region, and where the root filesystem is stored (that is, instance store or EBS). Choose the image that is most appropriate for you and note its ID, which begins with
Choose an Instance Type
Amazon offers several instance types, which are summarized on the EC2 web site. As of the time of writing, the smallest and cheapest instance types are
t1.micro, though each of those carries a restriction:
m1.small instances must use the i386 architecture.
t1.micro instances have no instance storage and therefore must boot from EBS. If the image you choose fits neither of these criteria or if you simply need more resources than they can provide then you need to use a larger and more expensive instance type.
Run an Instance
Run a new instance of the image and instance type you chose with
euca-run-instances. To be able to log into the new instance, you must also specify the name of the key pair you created earlier. For example, to run a
t1.micro instance of the image
ami-7f5a063a with a key pair named
mykey, run the following command:
$ euca-run-instances ami-7f5a063a -t t1.micro -k mykey RESERVATION r-4d5ea00a 0123456789ab default INSTANCE i-910fbbd6 ami-7f5a063a pending 0 mykey t1.micro 2011-10-11T00:00:00.000Z us-east-1c aki-9ba0f1de
The output of
euca-run-instances contains the ID of the instance you just started. In the example above, the instance's ID is
i-910fbbd6. You will need this ID to use tools that need to refer to the instance.
The instance starts in the
pending state. When they finish booting they change to the
running state. When you terminate them they change to the
shutting-down and finally
Log into the Instance
As the instance starts it obtains an IP address from EC2 and changes to the
running state. You can check on your instances by running
euca-describe-instances, optionally with the ID of the instance in question. When the instance is ready (or nearly ready) to use,
euca-describe-instances will display the address you can use to log into it:
$ euca-describe-instances RESERVATION r-4d5ea00a 0123456789ab default INSTANCE i-910fbbd6 ami-7f5a063a ec2-204-236-168-22.us-east-1.compute.amazonaws.com ip-10-170-15-23.us-east-1.compute.internal running 0 mykey t1.micro 2011-10-11T00:00:00.000Z us-east-1c aki-9ba0f1de
The public address of the instance in this example is
ec2-204-236-168-22.us-east-1.compute.amazonaws.com. Other useful bits of information from this command include the availability zone in which the instance is running (
us-east-1c) and the time that the instance started.
Once the instance is
running you can log into it with
ssh. On Fedora's images you should log in as the user ec2-user:
$ ssh -i mykey.pem firstname.lastname@example.org [ec2-user@i-910fbbd6 ~]$ cat /etc/fedora-release Fedora release 16 (Verne)
You can now use the instance as you would use any other computer running Fedora.
Terminate the InstanceWhen you finish using the instance you should terminate it with
euca-terminate-instancesto free up resources and reduce costs:
EBS volumes act like removable disks that you can attach to instances, except that you can create and destroy them at will. Each volume is specific to an availability zone. What follows are descriptions of how to use volumes.
You can create a volume of nearly any size, in 1 GiB increments. As of the time of writing, the maximum size of a volume is 1 TiB. To create a new, empty volume, choose a size (in GiB) and the availability zone in which to create it and supply those values to
$ euca-create-volume -s 10 -z us-east-1c VOLUME vol-23ca3542 10 creating 2011-10-11T00:00:00.000Z
The command's output contains the ID of the newly-created volume. In the example above, the volume's ID is
vol-23ca3542. You will need this ID to use tools that need to refer to the volume.
euca-describe-volumes will provide a list of all volumes available to you in the entire region in addition to where they are attached:
$ euca-describe-volumes VOLUME vol-23ca3542 10 us-east-1c available 2011-10-11T00:00:00.000Z
For an instance to make use of a volume you must first attach the volume to the instance. You also need to supply a device name that the volume should appear as from inside the instance. The device name you choose must be
X is a letter. It will appear inside the instance as either
euca-attach-volume -i i-910fbbd6 -d /dev/sdf vol-23ca3542
Once you have attached a volume to the instance it will appear as a disk in the instance's /dev directory, ready to be formatted and used.
[ec2-user@i-910fbbd6 ~]$ mkfs.ext4 /dev/xvdf [ec2-user@i-910fbbd6 ~]$ mount /dev/xvdf /mnt
When you finish using a volume you can unmount it from within the instance and then detach it:
[ec2-user@i-910fbbd6 ~]$ umount /dev/xvdf [ec2-user@i-910fbbd6 ~]$ logout $ euca-detach-volume vol-23ca3542
Deleting VolumesWhen you finish using a volume you can delete it to free up resources and reduce costs:
Volume snapshots provide an easy way to save a backup copy of an entire volume. Unlike a volume, a snapshot is available to all availability zones within a region, which makes snapshots the simplest way to copy a volume between availability zones.
Creating a Snapshot
You can create a snapshot by providing the name of the volume you wish to take a snapshot of to
$ euca-create-snapshot vol-23ca3542 SNAPSHOT snap-00acc96e vol-23ca3542 pending 2011-10-11T00:00:00.000Z
The command's output contains the ID of the newly-created snapshot. In the example above, the snapshot's ID is
snap-00acc96e. You will need this ID to use tools that need to refer to the snapshot.
euca-describe-snapshots will provide a list of all snapshots available to you in the region:
$ euca-describe-snapshots SNAPSHOT snap-00acc96e vol-042d3a6a completed 2011-10-12T05:56:29.000Z 100%
Creating Volumes from SnapshotsTo copy the contents of a snapshot to a new volume, run
euca-create-volumeand specify a snapshot instead of a size:
euca-create-volume --snapshot snap-00acc96e -z us-east-1c
You can create multiple volumes from the same snapshot. Each volume will be independent of the others.
To delete a snapshot, use
euca-delete-snapshot. Any volumes created from that snapshot will be unaffected.