Grab SSH hostkeys for a newly launched AWS EC2 instance

aws-instance-sshhostkeys

#!/bin/sh -eu
#
# Usage:
#   aws-instance-sshhostkeys i-deadbeef | tee -a .ssh/known_hosts

# FIXME:
#   Strip trailing CR
#   Strip trailing comment field
#   Support Route53 entries automatically

prog="$(basename "$0")"

if [ $# -eq 0 ]; then
  printf >&2 "Usage: %s %s\n" "$prog" "i-deadbeef i-beef2000 | tee -a .ssh/known_hosts"
  exit 1
fi

# {{{TestData
output_after=$(( $(date +%s) + 3 ))
testing_dummy_aws() { cat <<'EODUMMY'
{ "Reservations": [
  { "Instances": [
    { "NetworkInterfaces": [
      { "Status": "unwanted", "Association": { "PublicDnsName": "uh-oh", "PublicIp": "192.0.2.1" } },
      { "Status": "in-use", "Association": { "PublicDnsName": "dummyhost", "PublicIp": "192.0.2.42" } }
      ]
    }
    ]
  }
  ]
EODUMMY
  if [ $(date +%s) -ge $output_after ]; then
    cat <<'EODUMMY'
, "Output": "lorem ipsum\n-----BEGIN SSH HOST KEY KEYS-----\nssh-rsa 12345dummy54321\nssh-foo wibblepubkey\n-----END SSH HOST KEY KEYS-----\nblah\n"
EODUMMY
  fi
  echo "}"
}
# }}}TestData

if [ -n "${TESTING_AWS_INSTANCE_SSHHOSTKEYS:-}" ]; then
  aws() { testing_dummy_aws "$@" ; }
fi

for instance ; do

  prefix=$(
    aws ec2 describe-instances --instance-ids "$instance" | \
      jq -r '.Reservations[].Instances[].NetworkInterfaces[] | select(.Status == "in-use") | .Association | @text "\(.PublicDnsName),\(.PublicIp)"'
    )

  printf >&2 "%s: waiting for console log to have output: " "$prog"
  loop=true
  while $loop ; do
    if aws ec2 get-console-output --instance-id "$instance" | jq -e 'has("Output")' > /dev/null
    then
      printf >&2 " Have Output!\n"
      loop=false
    else
      printf >&2 "."
      sleep 5
    fi
  done

  aws ec2 get-console-output --instance-id "$instance" | jq -r .Output | \
    perl -ne 'print if /^-----BEGIN SSH HOST KEY KEYS-----\s*$/.../^-----END SSH HOST KEY KEYS-----\s*$/ and not /^-/' | \
    while read line; do
      printf "%s %s\n" "$prefix" "$line"
  done

done

# vim: set sw=2 et foldmethod=marker :

hrm, could have sworn that there was a loop around that sleep 5 ... that might have only been in a later version of this where I expanded it further for a previous employer and fixed such bugs. I no longer have access to that, only to this earlier developed-for-self variant.

Updated to give it a loop so that it actually waits, and some test data.