"ssm start-session" should print debug output to stderr instead of stdout

[heidemn]

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

• I've gone though the User Guide and the API reference
• I've searched for previous similar issues and didn't find any solution

Describe the bug

ssm start-session should enable the user to pipe stdout to a file or other command.
Currently, it dumps debug output to stdout, which is not helpful.

SDK version number
Same behavior with v1 and v2.
aws-cli/1.19.12 Python/3.8.5 Linux/4.19.128-microsoft-standard botocore/1.20.12
aws-cli/2.1.27 Python/3.7.3 Linux/4.19.128-microsoft-standard exe/x86_64.ubuntu.20 prompt/off

Platform/OS/Hardware/Device
Ubuntu 20.04.1 LTS (in WSL2)

To Reproduce (observed behavior)

$ aws ssm start-session --target i-0123456789abcde --document-name AWS-StartInteractiveCommand --parameters 'command=["echo 42"]' > 42.txt
(no output)

$ cat 42.txt

Starting session with SessionId: root-0001234567abcde
42


Exiting session with sessionId: root-0001234567abcde.

Expected behavior

$ aws ssm start-session --target i-0123456789abcde --document-name AWS-StartInteractiveCommand --parameters 'command=["echo 42"]' > 42.txt

Starting session with SessionId: root-0001234567abcde

Exiting session with sessionId: root-0001234567abcde.

$ cat 42.txt
42

Logs/output
n/a

Additional context
Use case: Run a command on the instance, and do some follow-up actions (local or remote) based on the output.

Unix commands generally print additional info to stderr.
Only the main output / payload should go to stdout.

I could find the text "Starting session" / "session with SessionId" neither in this repo, nor in the botocore repo.
-> I assume that this needs to be fixed in the session-manager-plugin, which seems not to be available on Github.

[kdaily]

Hi @heidemn, thanks for the report. You're right, this would need to be fixed in the session manager plugin. I will alert the SSM team to this feature request.

[kdaily]

You can open this issue here - unfortunately I do not have the permissions to transfer this issue to the other repository.

https://github.com/aws/amazon-ssm-agent

Thanks!

[github-actions]

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