aws-gate is written with easy debugging in mind. To activate a debug output, just set GATE_DEBUG environment variable and on the next invocation aws-gate will start producing debug output:
% export GATE_DEBUG=1
% aws-gate session ssm-test
2019-05-26 01:18:23,535 - aws_gate.config - DEBUG - Located config file: /Users/xenol/.aws-gate/config
2019-05-26 01:18:23,538 - aws_gate.utils - DEBUG - Obtaining boto3 session object
2019-05-26 01:18:23,549 - aws_gate.utils - DEBUG - Obtained configured AWS profiles: default development preproduction production
2019-05-26 01:18:23,550 - aws_gate.utils - DEBUG - Obtaining boto3 session object
2019-05-26 01:18:23,560 - aws_gate.utils - DEBUG - Obtained configured AWS profiles: default development preproduction production
2019-05-26 01:18:23,560 - aws_gate.utils - DEBUG - Obtaining boto3 session object
2019-05-26 01:18:23,574 - aws_gate.utils - DEBUG - Obtaining ssm client
2019-05-26 01:18:23,608 - aws_gate.utils - DEBUG - Obtaining boto3 session object
2019-05-26 01:18:23,636 - aws_gate.utils - DEBUG - Obtaining ec2 boto3 resource
2019-05-26 01:18:23,694 - aws_gate.query - DEBUG - Querying EC2 API for instance identifier: ssm-test
2019-05-26 01:18:24,029 - aws_gate.query - DEBUG - Found 1 maching instances
2019-05-26 01:18:24,030 - aws_gate.query - DEBUG - Matching instance: i-0772e4c1dcdd763b6
2019-05-26 01:18:24,030 - aws_gate.session - INFO - Opening session on instance i-0772e4c1dcdd763b6 (eu-west-1) via profile default
2019-05-26 01:18:24,030 - aws_gate.session - DEBUG - Creating a new session on instance: i-0772e4c1dcdd763b6 (eu-west-1)
...
When you run into a problem with aws-gate or something is not working as described, please do not hesitate and open an issue in the project's issue tracker.