Can I assign a firewall while creating a droplet via API?

One of possible solutions is to use tags. You can create a firewall and assign it a tag, and then use that tag on Droplet creation. That way, all rules defined in the firewall will be applied to all Droplets with the assigned tag.

I would suggest taking a look at something like terraform to do your droplet provisioning.

resource "digitalocean_droplet" "web" {
  name      = "web-1"
  size      = "512mb"
  image     = "centos-7-x64"
  region    = "nyc3"
}

resource "digitalocean_firewall" "web" {
  name = "only-22-80-and-443"

  droplet_ids = ["${digitalocean_droplet.web.id}"]

  inbound_rule = [
    {
      protocol           = "tcp"
      port_range         = "22"
      source_addresses   = ["192.168.1.0/24", "2002:1:2::/48"]
    },
    {
      protocol           = "tcp"
      port_range         = "80"
      source_addresses   = ["0.0.0.0/0", "::/0"]
    },
    {
      protocol           = "tcp"
      port_range         = "443"
      source_addresses   = ["0.0.0.0/0", "::/0"]
    },
  ]

  outbound_rule = [
    {
      protocol                = "tcp"
      port_range              = "53"
      destination_addresses   = ["0.0.0.0/0", "::/0"]
    },
    {
      protocol                = "udp"
      port_range              = "53"
      destination_addresses   = ["0.0.0.0/0", "::/0"]
    },
  ]
}

https://www.terraform.io/docs/providers/do/index.html

I honestly really want to do this from my main droplet to make things easier, the way I have it setup everything is automated to create droplets, set the droplets up, alert the clients, etc.

My alternative to automatically assigning the firewall is basically something like this as a daily cron job (work in progress) if Digital Ocean doesn’t support assigning a firewall during droplet creation…

Although I will be working on the logic to prevent unnecessary API calls and I do see a logic flaw in the code as it stands right now.

#!/bin/bash
TOKEN='xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';
FIREWALLID='xxxxxxxxxxxxxxxxxxxxxx';
# ITERATE THROUGH ALL DROPLETS 1 AT A TIME FOR EASIER PARSING
for i in {1..1000}; do
	if ! (curl -X GET -H "Content-Type: application/json" -H "Authorization: Bearer 00567194053b404e749f72a3f409d7af595e34517436ae303f411cfa1f1cdeeb" "https://api.digitalocean.com/v2/droplets?page=$i&per_page=1" | grep -qviE "droplets|to|exclude"); then
		DROPLETID=$(curl -X GET -H "Content-Type: application/json" -H "Authorization: Bearer 00567194053b404e749f72a3f409d7af595e34517436ae303f411cfa1f1cdeeb" "https://api.digitalocean.com/v2/droplets?page=1&per_page=1" | awk -F"," '{print $1}' | awk -F'"id":' '{print $2}');
		echo "$DROPLETID" > /tmp/lastdroplet.txt;


			if ( "$(cat /tmp/lastdroplet.txt)" != "$DROPLETID" ); then
				if !(grep -q $DROPLETID /root/firewalled-droplets.txt); then
					curl -X POST -H "Content-Type: application/json" -H "Authorization: Bearer $TOKEN" -d '{"droplet_ids":['"$DROPLETID"']}' "https://api.digitalocean.com/v2/firewalls/$FIREWALLID/droplets";
					echo $DROPLETID >> /root/firewalled-droplets.txt;
				fi;
			else
				echo "All droplets have been added to firewall, exiting.";
				exit 0;
			fi;



	fi;
done;