Connect to Linux EC2 Instance if Key pair is lost after Initial Launch

By

Use Case

We know that EC2 Linux instances are accessible through the private keys by default. However, SSH is allowed but you cannot use SSH password authentication to access Linux instance as it is disabled by default. So, what would happen if you lose the private key of your Linux instance? In this blog, I will walk you through the easiest ways to login when you lost the Key pair

What is a key-pair file?

Key-pair is a combination of a public and private key. Amazon EC2 uses public-key cryptography to encrypt and decrypt login information. Private key is only the way to get access to the instance, what if you lost the key? Is your servers lost in black hole? Thankfully nothing is lost you still can access your server, let me show you how can you solve this problem.

Things that you should know before to proceed to this topic

  • This procedure will requires start and stop of your instance. Hence, please keep in mind that data in instance store volumes will be lost. Make sure that you backup any data on the instance store volume that you want to keep
  • Stopping and starting the instance changes the public IP address of the instance. Its a best practice to use an Elastic IP address instead of a public IP address when routing external traffic to your instance

Methods

Method 1: Using user data

Create a new key pair. This can be done in two ways
  1. Open Amazon EC2 console, select network and security tab in left navigation pane and choose Key pairs. Choose create key pair and enter a name for the key pair and choose the format (PEM/PPK) according to your requirement and choose create key pair, key pair will be automatically download. keep the key pair in secured place.

    Retrieve the public key for the key-pair downloaded from AWS. generate the public key with below command:
    ssh-keygen -y -f recover-key-par.pem

  2. Generate a key pair with a third party tool of your choice. For example, you can use ssh-keygen. Alternatively, Java, Ruby, Python and many other programming language provide standard libraries that you can use to create RSA key pair.

    Save the public key to a local file. For example, ~/.ssh/id_rsa.pub
    Note that file name extension for this file is not important
In AWS management console, navigate to EC2 console and select the instance which you have lost the key-pair. Stop the instance


Once, instance is stopped. Select the Actions and choose Instance settings and select Edit user data. Copy the below script and paste it in user data

 
Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0

--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"

#cloud-config
cloud_final_modules:
- [users-groups, once]
users:
 - name:ec2-user
   ssh-authorized-keys:
   - PublicKeypair
Replace PublicKeypair with the ssh rsa keys which we generated above and save the user data and start the instance.

Once Instance is Up and running, connect to the EC2 instance with the key which you have passed in the user data. In this example, I will connect via Putty with PPK. In order to login to the Instance via Putty, you need to generate PPK via PuttyGen.

Open PuttyGen, select load and locate the PEM file and click on save private Key.
Open Putty, enter the IP address of the instance and in SSH and Auth browse the PPK file and click Open. Login with ec2-user and you should be able to authenticate with the Linux instance

Please note that since the script contains a key-pair, it is necessary to remove the script from the user data field after verifying that you are able to connect to the EC2 instance.

Method 2: Using AWS Systems Manager

If the instance is a managed instance in AWS Systems Manager, you can use the AWSSupport-ResetAccess document to recover the lost key pair.

Open the AWS Systems Manager console, select Automation in left navigation pane, click execute Automation. In automation document section select owned by Amazon. In the run book list, search for AWSSupport-ResetAccess

In Execute automation document page, choose Simple execution. In document details section, verify Document version is set to Default. In the input parameter section, specify the following parameter and execute.

InstanceId: Instance ID which is not reachable
SubnetId: Subnet ID where Unreachable instance is hosted
EC2RescueInstanceType: Specify the Instance Type for the EC2 Rescue Instance

When Automation is finished, choose the description tab and choose view outputs to validate the output.


For Linux instances, the new ssh private key is saved and encrypted in parameter store and the parameter store named as /ec2rl/openssh/<InstanceID>/key

You can ssh to the instance by using this key.
Note: The Automation workflow creates a backup, password-enabled Amazon Machine Images(AMI) that you may want to remove. To locate these AMI, In EC2 console, choose AMI from left navigation pane. Enter the automation execution ID in search field and locate the AMI.

Conclusion

In this blog post, I have shown you how to login to the Linux EC2 Instance if you have lost the key pair. Hope this blog helped you in your similar use case.

Thank you for reading!

Comments

Post a Comment

Popular posts from this blog

Setup Grafana on AWS EKS and integrate with AWS Cloudwatch

By
What is Grafana? Grafana is open-source visualization and analytics software. It allows you to query, visualize, alert on, and explore your metrics no matter where they are stored. In plain English, it provides you with tools to turn your time-series database (TSDB) data into beautiful graphs and visualizations. Setup Grafana on Amazon Elastic Kubernetes Service This blog explains on how to run Grafana on Amazon Elastic Kubernetes cluster and adding cloudwatch as datasource to Grafana. Using Grafana you can simplify Kubernetes monitoring dashboards from Clo
Read more

Start or Stop services in multiple Windows EC2 Instances using AWS Systems Manager

By
Use Case You are the admin over a large amount of EC2 instances and managing different AWS accounts under Organization and you have to start/stop/disable a service for all Windows EC2 Instances in the Organization. Rather than wasting labor hours to perform this activity in each instance manually, you want to automate the process using AWS Systems Manager. Recently Windows had a flaw in Print Spooler Remote Code Execution Vulnerability and Microsoft recommended to stop until the patch is applied, in order to apply this immediately, we can make use of this design Systems Manager Systems Manager (SSM) gives you visibility and control over your AWS infrastructure. Automation, a capability of AWS Systems Manager, simplifies common maintenance and deployment tasks of Amazon Elastic Compute Cloud (Amazon EC2) instances and other AWS resources. Automation helps you to do the following: Build automations to configure and manage instances and
Read more

Concourse CI Installation and Configuration in Windows

By
Introduction to Concourse Concourse is an open source CI/CD system with integration supported to Resource types in the outside world. Concourse's principles reduce the risk of switching to and from Concourse, by encouraging practices that decouple your project from your CI's little details, and keeping all configuration in declarative files that can be checked into version control. Install and Configure Concourse in Windows Follow the below Steps to Install Installing Docker Desktop is pretty simple, download the exe file and install the docker desktop Modify Docker daemon configuration file as below
Read more

Install SSM Agent in Amazon EC2 Instance

By
What is SSM Agent AWS Systems Manager Agent is a Amazon software which can be installed on Amazon EC2 Instances. If SSM Agent is Installed in the servers then it will be easy to manage the EC2 Instances through AWS Systems manager.  By default SSM agent is pre installed for below Amazon Machine Images Amazon Linux Amazon Linux 2 Amazon Linux 2 ECS-Optimized Base AMIs macOS 10.14.x (Mojave), 10.15.x (Catalina), and 11.x (Big Sur) SUSE Linux Enterprise Server (SLES) 12 and 15 Ubuntu Server 16.04, 18.04, and 20.04 Windows Server 2008-2012 R2 AMIs published in November 2016 or later Windows Server 2016 and 2019 In this blog, I will walk you through on the ways to Install SSM Agent in the Instances which will not get SSM Agent by default. Steps to Install S
Read more

AWS Route 53 Inbound Resolver to resolve DNS for Multi Account Organization

By
Amazon Route53 Resolver The route 53 resolvers are contactable IP addresses (endpoints) where the DNS queries from different sources can be directed. There are two types of resolvers that administrators can deploy. Inbound Resolver As the name says inbound (DNS Resolutions coming in) which will enable your resources in the on-prem network to resolve AWS resource domain names or records in a Route 53 private hosted zone by allowing your on-prem network DNS resolvers to forward queries to Route 53 Resolver. Outbound Resolver As the name says Outbound (DNS Resolutions going out) which will enable your AWS resources to resolve the domain names of your on-prem network resources using resolver rules, which would forward selected queries to the on-prem network DNS resolvers On-prem to AWS DNS Resolution for
Read more

Automate Permission Boundary Attachment to IAM roles and Users

By
When we are managing multiple AWS Accounts in an Organization and each accounts will have their own requirement but as a centralized admin, we should be having a certain governance and compliance framework. IAM is a widely used AWS service and IAM roles/users are common used entity in AWS. As a centralized Admin, when we provide access to create IAM roles, cloud consumers in the landing zone accounts would create Users and Roles and attach Administrative policy and bypass the governance framework. In this blog, I will be briefing on restricting this scenario using IAM permission boundary and also deploying this setup through automation. AWS supports permissions boundaries for IAM entities (users or roles). A permissions boundary is an advanced feature for using a managed policy to set the maximum permissions that an identity-based policy can grant to an IAM entity. An entity's permissions boundary allows
Read more

Deploy AWS infrastructure using Terraform and GitHub Actions

By
Terraform being an Infrastructure as a Code helps us to manage a lot of infrastructure for several platforms in a consistent manner.  In this blog, I will walkthrough on deploying a terraform code using  Github actions Terraform code to create S3 bucket In this blog, I will walkthrough each blocks in terraform to create an S3 bucket in AWS in automated workflow using GitHub Actions. Lets look into the Terraform files. To understand easily, I have created separate tf files for each purpose, but you can still use all in one tf file as per your convenient. You can use any name with tf extension, for better understanding I used following names. versions.tf
Read more

Import Existing Resources using Terraform

By
In this blog, I will walk you through the ways to import pre-existing cloud resources in terraform. Why Import is required? There will be a scenario, where you will have a stringent timeline to setup a cloud Infrastructure and it can lead to situations where infrastructure needs to be created manually due to time pressures, emergency releases or just the fact that the infrastructure exists, and terraform was never used in the first instance. In a worst case scenario, you can lose the terraform.tfstate file. Terraform import will be essential in most of all these scenarios. Let's Import With an understanding of why Import is required, let us begin by importing a simple AWS resource S3. Firstly, we need to setup the Terraform and AWS credentials locally, we will not go into the details of installing and setting AWS credentials in
Read more

Hosting AWS VPC Interface Endpoints in Shared Model

By
What is VPC Endpoint A VPC endpoint enables private connections between your VPC and supported AWS services. Endpoints are classified as Interface and Gateways endpoints. In this blog, I will be showing how to host interface endpoints in shared model Do you have Multi AWS Accounts in Organization? When you have multi accounts structure in your Organization then creating endpoints in each accounts will increase the costs and IPs, in this blog I will explain how you can deploy endpoints in Shared Services Account and associate the member accounts VPCs with Private Hosted zone. Below is the Architectural diagram which I will be showing in detail on how to setup and also how the flow works Architecture Design AWS Services/Components required VPC Subnets Endpoints Hosted zone and Record set Transit Gateway I
Read more