Infrastructure & Operations › Cloud Computing

Compute Instance (EC2)

A virtual server in the cloud.

Also known as: EC2, virtual server, cloud VM, VM instance

A compute instance is a virtual server you rent from a cloud provider. Amazon calls its version EC2; Google’s is Compute Engine; Azure calls them Virtual Machines. You pick an operating system image and a size, and a few minutes later you have a machine you can log into. It is a virtual machine running on the provider’s hardware.

You choose:

• Instance type: how many CPUs and how much memory (and sometimes a GPU or fast local disk).
• Image: the operating system and any preinstalled software.
• Storage: a network disk attached to it.
• Region and zone: where it physically runs. See regions and AZs.
• Network rules: which ports are open. See security groups.

# e.g. with the AWS CLI (IDs and names are placeholders)
aws ec2 run-instances --image-id ami-0abc... --instance-type t3.small --key-name my-key

What you are responsible for

An instance is like a server in your own data centre: you patch the OS, secure access, install and update software, and back up the data. For less work, there are managed alternatives. See IaaS, PaaS and SaaS.

Common mistakes

• Leaving it running. Instances bill by time while they run, even when idle. Stop or delete what you don’t use.
• Opening SSH (port 22) to the whole internet in the firewall rules. Restrict it to your own IP or use a bastion or the provider’s session tooling.
• Storing important data only on the instance. Some instance types have temporary local disks that are lost when the instance stops. Use attached persistent volumes or a managed service.
• Hand-configuring one special server that nobody can rebuild.
• Wrong size. Too small makes the app slow, too large wastes money; measure and resize.