A golang implementation of the protocol used with AWS SSM sessions. The goal of this library is to provide an easy to digest way of integrating AWS SSM sessions to Go code without needing to rely on the external session manager plugin.
Simple, single stream port forwarding is available through the ssmclient.PortForwardingSession() function. This
function takes an AWS SDK client.ConfigProvider type (which can be satisfied with a session.Session), and a
ssmclient.PortForwardingInput pointer (which contains the target instance and port to connect to, and the local port
to listen on). See the example for a simple implementation.
Shell-level access to an instance can be obtained using the ssmclient.ShellSession() function. This function takes
an AWS SDK client.ConfigProvider type (which can be satisfied with a session.Session), and a string to identify the
target to connect with. For now, this client has only been tested on macOS and Linux, connecting to a Linux target.
See the example for a simple implementation.
SSH over SSM integration can be leveraged via the ssmclient.SshSession() function. Since the SSM SSH integration is
a specialized form of port forwarding, the function takes the same arguments as ssmclient.PortForwardingSession().
The difference being that any LocalPort configuration is ignored, and if no RemotePort is provided, the defaule value
of 22 is used. See the example for a simple implementation, which can be used in the SSH
configuration to enable connecting via SSH.
This feature is meant to be used in SSH configuration files according to the AWS documentation except that the ProxyCommand syntax changes to:
ProxyCommand sh -c "name_of_program_using_this_library profile_name %h:%p"
Where profile_name is the AWS configuration profile to use (you should also be able to use the AWS_PROFILE environment variable, in which case the profile_name could be omitted), and %h:%p are standard SSH configuration substitutions for the host and port number to connect with, and can be left as-is.
A couple of helper functions are available to assist with looking up values for EC2 instance IDs. The
ssmclient.ResolveTarget() and ssmclient.ResolveTargetChain() functions can be used to find an instance ID
using friendlier, or better known identifying information for an instance.
The ssmclient.ResolveTarget() function uses a predetermined lookup order to find an instance. If provided with a
non-nil AWS SDK client.ConfigProvider (which can be satisfied with a session.Session), instance tags, or the private
IPv4 address of the instance can be used. If those avenues do not yield an instance ID, then a DNS TXT record lookup
is performed.
The ssmclient.ResolveTargetChain() function accepts a varargs list of types implementing the TargetResolver interface
to perform the instance ID resolution. This allows custom resolution logic to be added in case the provided mechanisms
prove insufficient.
- Shell sessions to Windows EC2 instances and from Windows to anywhere.
- Allow multiplexed connections (multiple, simultaneous streams) with port forwarding
- Robustness (retries/error recovery, out of order message handling)
The source code for the AWS SSM agent, which is a useful reference for grokking message formats, and the
expected interaction with the various services of the agent.
https://github.com/aws/amazon-ssm-agent/tree/master/agent/session
The contracts directory contains definitions of the various types used for messaging, and the plugins, shell,
and datachannel directories can be a useful reference for how the protocol works.
The node.js library at https://github.com/bertrandmartel/aws-ssm-session was also very instructive for seeing and actual client-side implementation of the protocol for shell sessions.
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