Make it easier to set metadata_service_num_attempts and metadata_service_timeout programatically

[sirosen]

Right now, it's hard to set metadata_service_num_attempts and metadata_service_timeout in application code.
Whereas some settings are trivial to set on a per-client basis (e.g. region=...), some require a layer of indirection (e.g. via creating a custom Config object).

However, in the case of these parameters, I think the shortest path to setting these in my application would be something like

def boto3_session(**kwargs):
    botocore_session = botocore.session.get_session()
    botocore_session.set_config_variable('metadata_service_timeout', 5)
    botocore_session.set_config_variable('metadata_service_num_attempts', 2)
    return boto3.session.Session(botocore_session=botocore_session, **kwargs)

This is verbose and awkward for setting something which is supported in config and environment variables.
And it requires that all client instantiations use explicit session objects in order to set a config flag.

I think my ideal solution would be for botocore.config.Config to support these settings, and then for the boto3 clients to pass them through the underlying session machinery so that these are supported as part of the retry config.

If these are already supported via Config, then I would claim that the current documentation does not make this sufficiently clear, and ask that we enhance it to cover this usage. (I'm happy to open a PR with sufficient direction about where to update things.)
Even if this is something which is considered primarily a botocore issue, I think the boto3 docs should explain how to set these values.

[swetashre]

Thank you for your post. Marking this as feature request.

[github-actions]

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[sirosen]

The auto-close happening over a 3-day period is a little short, especially as I wasn't working on Friday. Can this be reopened? There's been no activity because I don't want to nag -- I assume the original issue is clear and sufficient.