Useful AWS bash function - resource_exists() - for pre-checking and avoiding collisions

aws-resource-exists.bash

#!/bin/bash

# written and explained by others!
# https://blogs.aws.amazon.com/cli/post/Tx93V7O09I96SO/AWS-re-Invent-2015-and-more
# https://github.com/awslabs/awscli-reinvent2015-examples/blob/master/scripts/setup-dev-ec2-instance

# Note: you need "jp" installed
# to run this command.  You can
# brew tap jmespath/jmespath && brew install jp
# to install on a Mac.
# Or you can download prebuilt binaries
# from: https://github.com/jmespath/jp/releases

docs="usage: setup-dev-ec2-instance

This command will set up the necessary resources needed to run
dev-ec2-instance.  You can also use this script to check that
all the necessary resources are setup.  If any resources
are missing, it will prompt you to set up the necessary parts.
"

TRUST_POLICY='{
    "Version": "2008-10-17",
    "Statement": [
        {
            "Action": "sts:AssumeRole",
            "Principal": {
                "Service": "ec2.amazonaws.com"
            },
            "Effect": "Allow",
            "Sid": ""
        }
    ]
}'

errexit() {
  echo "ERROR: $(basename "$0") (line ${LINENO}): ${1:-"Unknown Error"}" 1>&2
  exit 1
}

usage() {
  echo "$docs"
}

## LOOK AT THIS!
resource_exists() {
  # Run a command with an added --query length(...)
  # and check if it results in at least a 1 element list.
  local command
  local num_matches
  set -e
  if [[ -z "$2" ]]
  then
    command="$1 --query length(*[0])"
  else
    command="$1 --query length($2)"
  fi
  num_matches=$($command)
  if [[ "$?" -ne 0 ]]
  then
    echo "Could not check if resource exists, exiting."
    exit 2
  fi
  set +e
  if [[ "$num_matches" -gt 0 ]]
  then
    # RC of 0 mean the resource exists, "success"
    return 0
  else
    return 1
  fi
}

has_new_enough_openssl() {
  # This is a quirk of openssl.
  # RC of 1 (an error) means the command
  # exists.  Otherwise an RC of 0 means
  # the command does *not* exist.  So
  # we have to reverse this because we want
  # RC 0 -> success/true
  # RC 1 -> fail/false
  openssl pkey -foobar 2>/dev/null
  if [[ "$?" -eq 0 ]]; then
    return 1
  fi
  return 0
}

import_key_pair() {
  echo -n "Would you like to import ~/.ssh/id_rsa.pub? [y/N]: "
  read confirmation
  if [[ "$confirmation" != "y" ]]
  then
    return
  fi
  aws ec2 import-key-pair \
    --key-name id_rsa \
    --public-key-material file://~/.ssh/id_rsa.pub
}

create_instance_profile() {
  echo -n "Would you like to create an IAM instance profile? [y/N]: "
  read confirmation
  if [[ "$confirmation" != "y" ]]; then
    return
  fi
  aws iam create-role --role-name dev-ec2-instance \
    --assume-role-policy-document "$TRUST_POLICY" || errexit "Could not create Role"

  # Use a managed policy
  policies=$(aws iam list-policies --scope AWS)
  admin_policy_arn=$(jp -u \
    "Policies[?PolicyName=='AdministratorAccess'].Arn | [0]" <<< "$policies")
  aws iam attach-role-policy \
    --role-name dev-ec2-instance \
    --policy-arn "$admin_policy_arn" || errexit "Could not attach role policy"

  # Then we need to create an instance profile from the role.
  aws iam create-instance-profile \
    --instance-profile-name dev-ec2-instance || \
    errexit "Could not create instance profile."
  # And add it to the role
  aws iam add-role-to-instance-profile \
    --role-name dev-ec2-instance \
    --instance-profile-name dev-ec2-instance || \
    errexit "Could not add role to instance profile."
}

compute_key_fingerprint() {
  # Computes the fingerprint of a public SSH key given a private
  # RSA key.  This can be used to compare against the output given
  # from aws ec2 describe-key-pair.
  openssl pkey -in ~/.ssh/id_rsa -pubout -outform DER | \
    openssl md5 -c | \
    cut -d = -f 2 | \
    tr -d '[:space:]'
}

tag_security_group() {
  aws ec2 describe-security-groups --query "SecurityGroups[].[GroupName,GroupId,VpcId]" --output text | column -t
  echo -n "Enter the security group ID to tag: "
  read response
  if [ -z "$response" ]; then
    return
  fi
  echo "Tagging security group"
  aws ec2 create-tags --resources "$response" --tags Key=dev-ec2-instance,Value=linux
}

do_setup() {
  echo "Checking for required resources..."
  echo ""
  # 1. Check if a security group is found for
  #    both windows and non-windows tags.
  #    If not, we'll eventually give the option to
  #    configure this.
  if resource_exists "aws ec2 describe-security-groups \
    --filter Name=tag:dev-ec2-instance,Values=linux"; then
    echo "Security groups exists."
  else
    echo "Security group not found."
    tag_security_group
  fi

  # 2. Make sure the keypair is imported.
  if [[ ! -f ~/.ssh/id_rsa ]]; then
    echo "Missing ~/.ssh/id_rsa key pair."
  elif has_new_enough_openssl; then
    fingerprint=$(compute_key_fingerprint ~/.ssh/id_rsa)
    if resource_exists "aws ec2 describe-key-pairs \
      --filter Name=fingerprint,Values=$fingerprint"; then
      echo "Key pair exists."
    else
      echo "~/.ssh/id_rsa key pair does not appear to be imported."
      import_key_pair
    fi
  else
    echo "Can't check if SSH key has been imported."
    echo "You need at least openssl 1.0.0 that has a \"pkey\" command."
    echo "Please upgrade your version of openssl."
  fi

  # 3. Check that they have an IAM role called dev-ec2-instance.
  #    There is no server side filter for this like we have with the EC2
  #    APIs, so we have to manually use a --query option for us.
  if resource_exists "aws iam list-instance-profiles" \
    "InstanceProfiles[?InstanceProfileName=='dev-ec2-instance']"; then
    echo "Instance profile exists."
  else
    echo "Missing IAM instance profile 'dev-ec2-instance'"
    create_instance_profile
  fi
  echo "Setup complete, you can now run: ./dev-ec2-instance"
}

do_setup