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Let's SSM, not SSH, on EC2 instances

Suraj Narwade's photo
Suraj Narwade
·Feb 20, 2023·

3 min read

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To access EC2 instances, SSH has been the preferred way for many years. But this way has its downsides, such as managing the keypairs, etc.

Recently, I came across a new safe and secure way to access instances, even from a Web browser and from the terminal, which is SSM. Let's learn more about SSM and how to set it up.

What is SSM?

SSM stands for Systems Manager, a set of tools such as Session manager, State manager, patch manager, etc.

Among all of them, we are going to focus on Session Manager as a replacement for SSH.

What is SSM Session Manager?

Session Manager is a feature of AWS Systems Manager (SSM) that allows you to establish secure, bi-directional connectivity between your local computer and an Amazon Elastic Compute Cloud (EC2) instance using a web-based shell or the AWS CLI.

Key features of SSM Session Manager

Some of the key features of Session Manager are as follows:

  1. Secure communication using IAM and SSL.

  2. Fine-grained access control: With the IAM policy's help, you can control who has access to start sessions and require MFA for added security.

  3. Audit: It logs all session activity, providing a complete audit trail of who accessed an instance and what actions were performed.

Supported Operating Systems:

  • Amazon Linux 2

  • Amazon Linux

  • Ubuntu Server

  • Red Hat Enterprise Linux (RHEL)

  • SUSE Linux Enterprise Server (SLES)

How does it work?

You will need to install the SSM agent on your EC2 machine. Amazon Linux or EKS Optimised AMIs comes with pre-installed SSM agents.

Refer to this documentation to install SSM Agent: https://docs.aws.amazon.com/systems-manager/latest/userguide/sysman-manual-agent-install.html.

Verify that the agent is installed,

sudo systemctl status amazon-ssm-agent

Now that agent is installed, we will need to give appropriate IAM permissions to the EC2 instance.

We will need to attach the default IAM Policy AmazonSSMManagedInstanceCore to the IAM role of the EC2 instance.

If you cannot use default policies, follow this documentation and manually create the policy: https://docs.aws.amazon.com/systems-manager/latest/userguide/getting-started-add-permissions-to-existing-profile.html.

Accessing the instance via Browser

  • To access the instance using SSM, head over to the EC2 console.

  • Select the EC2 instance you wish to access.

  • Click on Connect and now select Session Manager and then click on Connect

  • It will open a new tab in your browser with shell access to your instance.

Accessing the instance via AWS CLI

  • To access the instance using AWS CLI, you will need a session manager plugin for AWS CLI

  • Follow this documentation to install the plugin: https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html

  • Verify that the plugin is installed by running the following command,

  •   $ session-manager-plugin
      The Session Manager plugin is installed successfully. Use the AWS CLI to start a session.
    
  • Now you can run the following command to connect to the instance

      aws ssm start-session --target <instance-id>
    

    In This way, you can completely ditch SSH and start using SSM to access your EC2 instances.

    I hope you learned something new from this blog post. Click here to learn about me and how you can support my work, Thank you.

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