SSM startSession does not work with AWS-StartPortForwardingSession

[dmattia]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone though Developer Guide and API reference
• I've checked AWS Forums and StackOverflow for answers
• I've searched for previous similar issues and didn't find any solution

Describe the bug
Forwarding remote ports to local ports does not work through the SDK.

Is the issue in the browser/Node.js?
Node.js

If on Node.js, are you running this on AWS Lambda?
No

Details of the browser/Node.js version
v12.14.0

SDK version number
v2.638.0

To Reproduce (observed behavior)

    const params = {
      DocumentName: "AWS-StartPortForwardingSession",
      Target: "i-<my_instance>",
      Parameters: {
        portNumber: ["8200"],
        localPortNumber: ["8200"],
      }
    };
    await ssm.startSession(params).promise();

The above code runs, and the promise returns successfully without throwing any error. However, the specified local port is not bound to.

Expected behavior
I expected that local port 8200 would be bound to, just like if I had run

aws ssm start-session \
  --target "i-<my_instance>" \
  --document-name "AWS-StartPortForwardingSession" \
  --parameters '{"portNumber": ["8200"], "localPortNumber": ["8200"]}'

which does bind to my local port

[ajredniwja]

Hey @dmattia thank-you for reaching out, you are right about the behavior, it is because the feature has not been implemented yet. This is mentioned in the API reference. The Parameters being just a name space for future use by the service team which can also be confirmed in https://github.com/aws/aws-sdk-js/blob/bda2ee776a8e6435b529cde2ab9b86e006a95e30/apis/ssm-2014-11-06.min.json#L4016-L4022

Marking it as a feature request for the service team. Please reach out if you have any additional questions.

[peterwoodworth]

I've submitted this as a ticket, and received a couple responses from the team. There seems to be a misunderstanding here of how startSession works. Read the replies below, I've bolded the most important part:

There's a custom logic in aws ssm start-session aws cli implementation that after successful SSM Start-Session API call, the CLI triggers SessionManagerPlugin which handles PortForwarding. Session Manager is only available via aws cli or aws session manager console.

To clarify, the startsession call from the sdk is only the first step necessary in the protocol needed to initiate a session, port forwarding or otherwise. Any parameters in that API call would only modify the initial startSession request. The client code contained in the SessionManagerPlugin handles what type of session is created from the response, and subsequently, any parameters that are passed to the session itself.

[github-actions]

This issue is now closed.

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[decatur]

See answer to How to use session-manager-plugin command for how to achieve this with boto3 and Python.