Just a quick one today...

So I'm working on some Client Extensions and wanted to see the impact that deployment would have across virtual instances.

But, normally to access different virtual instances, you need different virtual hosts (domain names) in order to access the different instances.

But, when you're running locally, and maybe when you don't have access/permissions to write your /etc/hosts file, you might be wondering how you can access the other instances...

As it turns out, there is this funny rule in domain name resolution which effectively makes *.localhost resolve to 127.0.0.1/::1.

Now, this often won't be immediately clear. I mean, I dropped down to the command line to try some commands:

$ nslookup example.localhost
Server:		fe80::9691:7fff:fe47:ade1%21
Address:	fe80::9691:7fff:fe47:ade1%21#53

** server can't find example.localhost: NXDOMAIN

$ ping example.localhost
ping: cannot resolve example.localhost: Unknown host
$ dig example.localhost

; <<>> DiG 9.10.6 <<>> example.localhost
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 49884
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;example.localhost.		IN	A

;; Query time: 0 msec
;; SERVER: fe80::9691:7fff:fe47:ade1%21#53(fe80::9691:7fff:fe47:ade1%21)
;; WHEN: Mon Nov 25 15:00:19 EST 2024
;; MSG SIZE  rcvd: 46

Now this of course will lead you to believe this won't really work as you hoped, but trust me, it does.

When you try to access http://example.localhost:8080 in your browser, it will work. Likewise you can use the command:

$ curl -o /dev/null -s -w "%{http_code}\n" http://example.localhost:8080
200

So, on your local system, as long as you designate your virtual hosts using the *.localhost format, you'll be able to access the different virtual instances that you create on your system without changing the /etc/hosts file or really making any system changes at all.

Enjoy!