ssm-session-client

README

SSM Session Client CLI

This project is a fork of ssm-session-client with added CLI functionality to connect to AWS SSM sessions. The goal is to provide a single executable for SSM Session functionality, especially useful in environments where AWS CLI execution is restricted. Such as:

• Microsoft AppLocker
• AirLock
• Manage Engine

The main goal of this project is to enable SSM Client in complex environments where AWS Services endpoints (PrivateLink) are accessible from private networks via VPN or Direct Connect.

When the SSM StartSession is called, the API will return the StreamUrl with the regional SSM Messages endpoint. Even if SSM Messages endpoint is reachable in a private network, the only options to use it are HTTPS proxy or DNS RPZ. For this reason, this app has a flag to set the SSM Messages endpoint, then it will replace the StreamUrl with your SSM Messages endpoint.

Note: Windows SSH Client is not installed by default.

Requirements

1. Download the executable from Releases and copy it to the target operating system.
2. (Optional) Install the Session Manager plugin. It is recommended and will be used by default if installed.

Configuration

First, follow the standard configure AWS SDK and Tools to provide AWS credentials.

The utility can be configured via:

1. Configuration file: Default is $HOME/.ssm-session-client.yaml. It will also search in: a. Current folder b. User's home folder c. Application folder
2. Environment Variables with the SCC_ prefix
3. Command Line parameters

These are the configuration options:

Description	App Config/Flag	App Env Variable	AWS SDK Variable
Config File Path	config	SCC_CONFIG	n/a
AWS SDK profile name	aws-profile	SCC_AWS_PROFILE	AWS_PROFILE
AWS SDK region name	aws-region	SCC_AWS_REGION	AWS_REGION or AWS_DEFAULT_REGION
STS Endpoint	sts-endpoint	SCC_STS_ENDPOINT	AWS_ENDPOINT_URL_STS
EC2 Endpoint	ec2-endpoint	SCC_EC2_ENDPOINT	AWS_ENDPOINT_URL_EC2
SSM Endpoint	ssm-endpoint	SCC_SSM_ENDPOINT	AWS_ENDPOINT_URL_SSM
SSM Messages Endpoint	ssmmessages-endpoint	SCC_SSMMESSAGES_ENDPOINT	n/a
Proxy URL	proxy-url	SCC_PROXY_URL	HTTPS_PROXY
SSM Session Plugin	ssm-session-plugin	SCC_SSM_SESSION_PLUGIN	n/a

Remarks

• The proxy-url flag is only applicable to services where custom endpoints are not set.
• The ssmmessages-endpoint flag is used to perform the WSS connection during an SSM Session by replacing the StreamUrl with the SSM Messages endpoint.
• The ssm-session-plugin flag specifies whether to use the AWS Session Manager plugin for the session.

Sample config file

ec2-endpoint: vpce-059c3b85db66f8165-mzb6o9nb.ec2.us-west-2.vpce.amazonaws.com
ssm-endpoint: vpce-06ef6f173680a1306-bt58rzff.ssm.us-west-2.vpce.amazonaws.com
ssmmessages-endpoint: vpce-0e5e5b0c558a14bf2-r3p6zkdm.ssmmessages.us-west-2.vpce.amazonaws.com
sts-endpoint: vpce-0877b4abeb479ee06-arkdktlc.sts.us-west-2.vpce.amazonaws.com
aws-profile: sandbox
proxy-url: http://myproxy:3128

Supported modes

Shell

Shell-level access to an instance can be obtained using the shell command. This command requires an AWS SDK profile and a string to identify the target instance.

Note: If you have enabled KMS encryption for Sessions, you must use the AWS Session Manager plugin.

$ssm-session-client shell i-0bdb4f892de4bb54c --config=config.yaml

IAM: Sample IAM policies for Session Manager

SSH

SSH over SSM integration can be used via the ssh command. Ensure the target instance has SSH authentication configured before connecting. This feature is meant to be used in SSH configuration files according to the AWS documentation.

You need to configure the ProxyCommand $HOME/.ssh/config (Linux/macOS) or %USERPROFILE%\.ssh\config (Windows).

# SSH over Session Manager
Host i-*
  ProxyCommand ssm-session-client ssh %r@%h --ssm-session-plugin=true --config=config.yaml

Then to connect:

$ssh ec2-user@i-0bdb4f892de4bb54c

IAM: Controlling user permissions for SSH connections through Session Manager

SSH with Instance Connect (Linux targets only)

SSH over SSM with EC2 Instance Connect can be used via the instance-connect command. This configuration is similar to the SSH setup above, but SSH authentication configuration is not required. Authentication is managed by the IAM action ec2-instance-connect:SendSSHPublicKey.

In this mode, the app will attempt to use default public SSH keys (id_ed25519.pub and id_rsa.pub) for temporary SSH authentication. Alternatively, you can specify a custom public key file using the ssh-public-key-file flag.

Note: EC2 Instance Connect endpoints are not available via AWS PrivateLink. Internet access or an Internet proxy is required to use this mode.

# SSH over Session Manager with EC2 Instance Connect and default SSH keys
Host i-*
  ProxyCommand ssm-session-client instance-connect %r@%h --ssm-session-plugin=true --config=config.yaml

# SSH over Session Manager with EC2 Instance Connect and custom SSH keys
Host i-*
  IdentityFile ~/.ssh/custom
  ProxyCommand ssm-session-client instance-connect %r@%h --ssm-session-plugin=true --config=config.yaml --ssh-public-key-file=~/.ssh/custom.pub

Then to connect:

$ssh ec2-user@i-0bdb4f892de4bb54c

IAM:

• Controlling user permissions for SSH connections through Session Manager
• Grant IAM permissions for EC2 Instance Connect

Port Forwarding

Port Forwarding via SSM allows you to securely create tunnels between your instances deployed in private subnets without needing to start the SSH service on the server, open the SSH port in the security group, or use a bastion host. It can be used via the port-forwarding command. If a local port is not provided, SSH will assign a random local port.

# SSH Port Forwarding from local port 8888 to instance port 443
$ssm-session-client port-forwarding i-0bdb4f892de4bb54c:443 8888 --config=config.yaml

Target Lookup

The target can be an instance ID, hostname or even IP address. The app uses a few functions to resolve the target.

Building from source

To build this Go project, ensure you have Go installed on your system. You can download and install it from the official Go website.

1. Clone the repository:

git clone https://github.com/alexbacchin/ssm-session-client.git
cd ssm-session-client

1. Build the project for different operating systems:

For Linux:

GOOS=linux GOARCH=amd64 go build -o ssm-session-client-linux main.go

For macOS:

GOOS=darwin GOARCH=amd64 go build -o ssm-session-client-macos main.go

For Windows:

GOOS=windows GOARCH=amd64 go build -o ssm-session-client.exe main.go

This will create an executable file named ssm-session-client in the current directory.

You can now use the ssm-session-client executable as described in the sections above.

TODO

• EC2 Instance Connect automatically generate disposable SSH key pair for SSH authentication
• Unit testing
• Allow multiplexed connections (multiple, simultaneous streams) with port forwarding
• Robustness (retries/error recovery)

Documentation

Overview

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