SSH Config for AWS EC2 Instances

SSH Config for AWS EC2

AWS EC2 instances use key pair authentication instead of passwords. Setting up proper SSH config entries simplifies connecting to your instances without remembering IP addresses and key file locations.

Example Config

Host my-ec2-web
  HostName ec2-52-14-123-45.us-east-2.compute.amazonaws.com
  User ec2-user
  IdentityFile ~/.ssh/my-ec2-keypair.pem
  IdentitiesOnly yes
  StrictHostKeyChecking no
  ServerAliveInterval 60
  ServerAliveCountMax 3

Host my-ec2-ubuntu
  HostName 10.0.1.50
  User ubuntu
  IdentityFile ~/.ssh/my-ec2-keypair.pem
  IdentitiesOnly yes
  ProxyJump my-ec2-web

Default Usernames by AMI

AMI Type	Default User
Amazon Linux / AL2023	ec2-user
Ubuntu	ubuntu
Debian	admin
CentOS	centos
RHEL	ec2-user
SUSE	ec2-user

PEM File Permissions

AWS-downloaded key pairs have a .pem extension. SSH requires strict permissions:

chmod 400 ~/.ssh/my-ec2-keypair.pem

StrictHostKeyChecking

Setting StrictHostKeyChecking no is common for EC2 because instances are frequently terminated and recreated, producing new host keys. However, this reduces security. For long-lived instances, use StrictHostKeyChecking ask instead.

Using Elastic IPs

If your instance has an Elastic IP, use it in the HostName for a stable address that survives instance stops and starts.

EC2 Instance Connect Alternative

For instances in private subnets, AWS Systems Manager Session Manager provides an alternative to direct SSH that doesn't require inbound security group rules or a bastion host.