How to Test Any Domain with curl’s --resolve Without Editing Hosts

We often encounter situations where a service changes its IP, is deployed on multiple servers, or uses a CDN, and we need to test a specific IP without affecting users.

For example, accessing http://fuckcloudnative.io with a custom IP 1.1.1.1 .

The obvious solution is to edit the hosts file: 1.1.1.1 fuckcloudnative.io This works but requires flushing the DNS cache and remembering to remove the entry later.

Using curl, we can specify the Host header directly, but that fails with HTTPS.

curl provides the --resolve option, which lets you bind a host:port pair to a custom address, working for both HTTP and HTTPS.

--resolve <host:port:address[,address]...>
    Provide a custom address for a specific host and port pair.
    Using this, you can make the curl request use the specified address
    and prevent the normally resolved address from being used.

Examples:

$ curl http://fuckcloudnative.io/ --resolve fuckcloudnative.io:80:1.1.1.1
$ curl https://fuckcloudnative.io/ --resolve fuckcloudnative.io:443:1.1.1.1

You can also use a wildcard to apply the IP to all hosts on a given port:

$ curl https://fuckcloudnative.io/ --resolve *:443:1.1.1.1