[#327] Add Connect-to-Bastion-via-SSM wiki page

Author: tung-nimblehq

.github/wiki/Connect-to-Bastion-via-SSM.md

@@ -0,0 +1,85 @@
+## Overview
+
+AWS Systems Manager Session Manager is the recommended approach for connecting to bastion instances. It eliminates the need for SSH key pairs and provides better security, auditability, and access control.
+
+### Why Use SSM Instead of Key Pairs?
+
+Traditional SSH key pairs have several drawbacks:
+
+- **Security Risk:** Key pairs are often shared across teams, increasing the attack surface.
+- **Lack of Auditability:** Difficult to track who accessed the bastion and what commands were executed.
+- **Rigid Access Control:** Revoking access requires deleting the entire key pair, affecting all users.
+- **Management Overhead:** AWS doesn't store key pairs after creation - if lost, recovery is impossible.
+
+## Prerequisites
+
+Before connecting via SSM, ensure the following requirements are met:
+
+### 1. IAM Role Configuration
+
+The EC2 instance must have an IAM instance profile attached with the `AmazonSSMManagedInstanceCore` policy. This allows the SSM agent to communicate with AWS Systems Manager.
+
+### 2. SSM Agent Installation
+
+Ensure the SSM Agent is installed on your bastion host. Most Amazon Machine Images (AMIs) come with it pre-installed.
+
+To verify the SSM Agent status, run:
+
+```bash
+sudo systemctl status amazon-ssm-agent
+```
+Example:
+
+![Amazon SSM Agent Status](assets/images/ssm/amazon-ssm-agent.png)
+
+### 3. Security Group Configuration
+
+With SSM, you can eliminate all inbound SSH traffic (port 22) in your Security Groups. Only outbound HTTPS (port 443) is required for communication with SSM.
+
+> **Note**!\
+> This is a significant security improvement as it reduces the attack surface by closing the SSH port entirely.
+
+## Connecting to the Instance
+
+### Via AWS Console
+
+1. Navigate to the EC2 dashboard
+2. Select your bastion instance
+3. Click **Connect**
+4. Choose the **Session Manager** tab
+5. Click **Connect**
+
+### Via AWS CLI
+
+1. Install the [Session Manager plugin](https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html) for AWS CLI
+
+2. Connect using the following command:
+
+```bash
+aws ssm start-session --target {instance-id}
+```
+
+## Port Forwarding to Private Resources
+
+You can tunnel to private resources (like RDS databases) using SSM port forwarding:
+
+```bash
+aws ssm start-session \
+  --target {instance-id} \
+  --document-name AWS-StartPortForwardingSessionToRemoteHost \
+  --parameters '{"host":["your-rds-endpoint"],"portNumber":["5432"],"localPortNumber":["5432"]}'
+```
+
+## Benefits of SSM
+
+- **Centralized Access Control:** Manage access via IAM policies - grant/revoke access without touching the instance.
+- **Quick Response:** Immediately terminate all sessions in case of security incidents.
+- **No Public IP Required:** Connect to instances in private subnets via VPC Endpoints.
+- **Full Auditing:** Log every session and command to CloudWatch Logs or S3 for compliance.
+
+## Considerations
+
+- **Latency:** Session Manager tunnels traffic through AWS APIs, which may introduce slight lag compared to direct SSH connections.
+- **Logging Costs:** While SSM is free, storing session logs in CloudWatch or S3 incurs costs. Consider configuring lifecycle rules or retention periods to manage costs.
+
+For more information, refer to the [AWS Session Manager documentation](https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager.html).

.github/wiki/_Sidebar.md

@@ -16,3 +16,4 @@
 - [[Modify the Infrastructure Diagram | Modify infra diagram]]
 - [[Publishing]]
 - [[Running Trivy Locally]]
+- [[Connect to Bastion via SSM]]