You can modify the Droplets protected by a Firewall in the control panel by choosing Networking from the top navigation, then Firewalls. Selecting the Firewall you want to check or modify, then navigate to its Droplets tab.
On a Firewall’s Droplets tab, you will see the list of all the Droplets protected by the Firewall. Droplets that you’ve added individually will be shown on their own line. Droplets that you’ve added with a tag are shown below the tag.
To add another Droplet or tag to the Firewall, use the Add Droplets button.
To remove a Droplet or tag from a Firewall, use its More menu.
From the Firewall’s Droplet you can see which Droplets are affected by the Firewall you’re viewing. To see all the rules affecting a specific Droplet, you’ll need to view the individual Droplet’s Networking page.
To see what rules are applied to a Droplet, click the Droplet’s name, then visit its Networking page which is linked in the left-hand menu.
When you haven’t applied any Firewalls to the Droplet, the page displays a message saying as much and provides a Manage Firewalls button, which leads directly to the Firewalls overview page.
When you’ve applied a Firewall to the Droplet, the Firewall’s name will appear below the Firewalls section header, followed by its Inbound and Outbound rules.
When you’ve applied more than one Firewall to the Droplet, the name of each Firewall appears under the Firewalls header, and the union of all of the Firewalls’ rules is displayed:
If two Firewalls contain identical rules, only one will appear in the table.
You can click on any Firewall’s name to manage its rules.
The guide How to Organize Your DigitalOcean Cloud Firewalls provides detailed guidance on how to use multiple Firewalls to make your security strategy more explicit and flexible.