Allow aiodynamo to fetch credentials for snapstart lambdas. #196
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For snapstart, the lambda boots once to do any static init. Subsequently, this snapshotted version is used for handling subsequent requests. Normally for lambdas, the AWS credentials are in the environment. Since snapstart will reuse a snapshot of the running application, it can't pass in variables in this way since they need to be refreshed. Instead, the `AWS_CONTAINER_CREDENTIALS_FULL_URI` env var is set and the `ContainerMetadataCredentials` in aiodynamo should be used to get credentials if using `Credentials.auto()` to initialise. Unfortunately, it looks like AWS formats the expiration timestamps slightly differently for this API on lambda, including the microseconds now. The `parse_amazon_timestamp` function fails to parse the value, resulting in `ContainerMetadataCredentials` being rejected as a `ChainCredentials` candidate and we end up with no credentials at all. I can't really find a definitive documentation of what the format should be so I can point to it, but obviously we know the code as it is works on ECS/EC2 etc so we must continue to be able to parse those. I've simply added a fallback to use microseconds if the string has a full-stop in it. It seems botocore is using the `dateutil` package to handle their parsing: https://github.com/boto/botocore/blob/f49ead849aa5a4ea428d9f378de14db6f4c6d645/botocore/utils.py#L950
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For snapstart, the lambda boots once to do any static init.
Subsequently, this snapshotted version is used for handling subsequent
requests.
Normally for lambdas, the AWS credentials are in the environment. Since
snapstart will reuse a snapshot of the running application, it can't
pass in variables in this way since they need to be refreshed.
Instead, the
AWS_CONTAINER_CREDENTIALS_FULL_URIenv var is set and theContainerMetadataCredentialsin aiodynamo should be used to getcredentials if using
Credentials.auto()to initialise.Unfortunately, it looks like AWS formats the expiration timestamps
slightly differently for this API on lambda, including the microseconds
now. The
parse_amazon_timestampfunction fails to parse the value,resulting in
ContainerMetadataCredentialsbeing rejected as aChainCredentialscandidate and we end up with no credentials at all.I can't really find a definitive documentation of what the format should
be so I can point to it, but obviously we know the code as it is works
on ECS/EC2 etc so we must continue to be able to parse those. I've
simply added a fallback to use microseconds if the string has a
full-stop in it.
It seems botocore is using the
dateutilpackage to handle theirparsing:
https://github.com/boto/botocore/blob/f49ead849aa5a4ea428d9f378de14db6f4c6d645/botocore/utils.py#L950