====== EC2: SSH Access ======

**General Information**

Using SSH to gain access to AWS EC2 instances. 

**Checklist**
  * AWS Account
  * Basic VPC, Subnets, etc already setup

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====== EC2: Keys ======

If you generate a key pair through the Amazon console, you will download a .pem file.
  * This file contains your key pair (private and public) and is used in ssh commands to login

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You can extract just your public key and output it in RSA format that Linux authorized_keys files expect.<code bash>ssh-keygen -y -f MYKEYPAIR.pem</code>
  * The output string can appended to a user's file at /home/USERNAME/.ssh/authorized_keys for additional key access beyond the default.

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====== EC2: SSH Access ======

Accessing EC2 instances with a SSH key.

Pre-req Setup
  * Launch EC2 Instance
  * Create new key and download it or use existing SSH key pair
  * Transfer the .pem key to your system that you will jump from to AWS
  * Change permissions to read only for owner<code bash>chmod 400 keypair.pem</code>

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===== EC2: Direct SSH To Public Facing System =====

SSH to a system's public IP/DNS.

  * Pre-req Setup complete
  * SSH using the pem key as the identity to a system's public IP/DNS
    * AWS AMI<code bash>ssh -i keypair.pem ec2-user@public.ip.address.here</code>
    * CentOS AMI<code bash>ssh -i keypair.pem centos@public.ip.address.here</code>

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===== EC2: SSH Through Bastion Host =====

SSH to a bastion host that is public facing and hopping from there to systems with private addresses only.

  * Pre-req Setup complete
  * Start SSH Agent<code bash>eval $(ssh-agent -s)</code>
  * Add key to the agent<code bash>ssh-add keypair.pem</code>
  * SSH to the bastion host, forwarding the pem key
    * AWS Linux AMI<code bash>ssh -A ec2-user@public.ip.address.here</code>
    * CentOS AMI<code bash>ssh -A centos@public.ip.address.here</code>
  * Now on bastion host, SSH to the private address only instance
    * AWS Linux AMI<code bash>ssh ec2-user@private.ip.address.here</code>
    * CentOS AMI<code bash>ssh centos@private.ip.address.here</code>

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