A Bash script to establish an SSM tunnel given an EC2 machine name, private DNS name, or identifier.

initiate-ssm-connection.sh

#!/bin/bash

set -e

if [ ! "$1" ]
then
  echo "Expected a hostname of the instance as a parameter."
  exit 1
fi

# Input variables.
HOSTNAME="$1"
SSH_PORT="${2:-22}"

# Matching instance names, starting by `aws-`.
if [[ $HOSTNAME = aws-* ]]; then
  INSTANCE_ID=$(aws ec2 describe-instances \
    --filter "Name=tag:Name,Values=$HOSTNAME" \
    --query "Reservations[].Instances[?State.Name == 'running'].InstanceId[]" \
    --output text)
fi

# Matching instance identifiers, starting by `i-` or `mi-`.
if [[ $HOSTNAME = i-* || $HOSTNAME = mi-* ]]; then
  INSTANCE_ID=$HOSTNAME
fi

if [[ ! $INSTANCE_ID ]]; then
  echo "Could not resolve instance identifier for hostname '$HOSTNAME'."
  exit 1
fi

# Creating the SSM tunnel once we've resolved the
# instance identifier.
aws ssm start-session \
  --target $INSTANCE_ID \
  --document-name AWS-StartSSHSession \
  --parameters "portNumber=$SSH_PORT"