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Lawrence Ink
Lawrence Ink

Still Using SSH On AWS Check Out Session Manager Instead!


Still Using SSH On AWS Check Out Session Manager Instead!

Using the AWS Systems Manager console or Amazon EC2 console, you can start a session with a single click. Using the AWS CLI, you can also start a session that runs a single command or a sequence of commands. Because permissions to managed nodes are provided through IAM policies instead of SSH keys or other mechanisms, the connection time is greatly reduced.

The AWS Systems Manager console includes access to all the Session Manager capabilities for both administrators and end users. You can perform any task that is related to your sessions by using the Systems Manager console.

To use the AWS CLI to run session commands, you must be using version 1.16.12 of the CLI (or later), and you must have installed the Session Manager plugin on your local machine. For information, see (Optional) Install the Session Manager plugin for the AWS CLI.

You can also set up VPC Endpoints for Systems Manager using AWS PrivateLink to further secure your sessions. AWS PrivateLink limits all network traffic between your managed nodes, Systems Manager, and Amazon EC2 to the Amazon network. For more information, see Create VPC endpoints.

A session is a connection made to a managed node using Session Manager. Sessions are based on a secure bi-directional communication channel between the client (you) and the remote managed node that streams inputs and outputs for commands. Traffic between a client and a managed node is encrypted using TLS 1.2, and requests to create the connection are signed using Sigv4. This two-way communication allows interactive bash and PowerShell access to managed nodes. You can also use an AWS Key Management Service (AWS KMS) key to further encrypt data beyond the default TLS encryption.

When John sends that first command to start the session, the Session Manager service authenticates his ID, verifies the permissions granted to him by an IAM policy, checks configuration settings (such as verifying allowed limits for the sessions), and sends a message to SSM Agent to open the two-way connection. After the connection is established and John types the next command, the command output from SSM Agent is uploaded to this communication channel and sent back to his local machine.

For example, for an Amazon Elastic Compute Cloud (Amazon EC2) instance, the key pair file you created or selected when you created the instance. (You specify the path to the certificate or key as part of the command to start a session. For information about starting a session using SSH, see Starting a session (SSH).)

You must connect using the managed node account associated with the Privacy Enhanced Mail (PEM) certificate, not the ssm-user account that is used for other types of session connections. For example, on EC2 instances for Linux and macOS, the default user is ec2-user. For information about identifying the default user for each instance type, see Get Information About Your Instance in the Amazon EC2 User Guide for Linux Instances.

Ideally, you install the agent when the instance is bootstrapped; however, you can install it on a running EC2 instance or on a non-AWS host to which you already have access. For example, to bootstrap the agent on an Amazon Linux EC2 instance, install it using the package manager in the instance user data:

As written, the first rule will never match because the TCP protocol is the first protocol that will appear in the initial flow, starting with the TCP handshake. Therefore, when the flow starts, while the first rule will be evaluated, there will be no TLS protocol to match, so the drop rule will match instead and drop all of the traffic to To avoid this, you should write rules that only evaluate after a session has been established using the flow keyword, for example:

For the rule that allows inbound traffic, check the Source field. If the value is a single IP address, and if the IP address is not static, a new IP address will be assigned each


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