SSH Session via AWS Session Manager with SSH Agent Passthrough

aws_ssm_ssh.sh

#!/usr/bin/env bash

set -euo pipefail

randomPort="$((49152 + ($RANDOM % 16383)))"

function cleanup_jobs() {
    for i in $(jobs -p); do
        pkill -P $i
    done
}
trap cleanup_jobs EXIT

if [ "${1-x}" == 'x' ]; then
    echo 'Please pass an instance ID as the first parameter to this command (e.g. [<user>@]<instance-id>)' 1>&2
    exit 1
fi

fullTarget="$1"
userField="${fullTarget%%@*}"
instanceField="${fullTarget#*@}"

aws ssm start-session --target "$instanceField" \
  --document-name AWS-StartPortForwardingSession \
  --parameters "portNumber=22,localPortNumber=${randomPort}" &

sshArgs=('-o' 'ForwardAgent=yes' '-p' "$randomPort" '-o' 'StrictHostKeyChecking=no' '-o' 'UserKnownHostsFile=/dev/null')
if [ "$userField" != "$instanceField" ]; then
    sshArgs+=('-l' "$userField")
fi

while :; do
    nc -z localhost $randomPort && break || sleep 1
done

sleep 5

ssh "${sshArgs[@]}" localhost