WSL2 use "localhost" to access Windows service

You should use hostname.local to access Windows from WSL2 because that will use the correct IP. Note that hostname should be replaced with the result of the hostname command run in WSL2. You can check the IP by running ping $(hostname).local from WSL2.

You also need to add a firewall rule to allow traffic from WSL2 to Windows. In an elevated PowerShell prompt run this:

New-NetFirewallRule -DisplayName "WSL" -Direction Inbound  -InterfaceAlias "vEthernet (WSL)"  -Action Allow

The command above should allow you to access anything exposed by Windows from WSL, no matter what port, however bear in mind that any apps you've launched get an automated rule created for them when you first launch them, blocking access from public networks (this is when you get a prompt from Windows Firewall, asking whether the app should be allowed to accept connections from public networks).

If you don't explicitly allow, they will be blocked by default, which also blocks connections from WSL. So you might need to find that inbound rule, and change it from block to allow (or just delete it).

See info here:

https://github.com/microsoft/WSL/issues/4585#issuecomment-610061194

Well, your title and your question body don't seem quite aligned.

The question title says "use localhost", but then in the body you say "using a server name."

Accessing the Windows 10 service via the name "localhost" from WSL2? Let's just go with "no". I can think of a possibility of how to make it work, but it would be complicated.

But I think the second is really what you are looking for, so a couple of options that I can think of for accessing the Windows host services by hostname in WSL2:

• First, and hopefully the easiest, WSL2 supports mDNS (WSL1 did not), so you should be able to access the Windows host as {hostname}.local (where {hostname} is the name of the Windows host (literally, in bash, ping $(hostname).local, since the assigned WSL2 hostname is that of the host Windows 10 computer). That works for me. While I don't recall having to do anything special to enable this, this Super User answer seems to indicate that you have to turn it on manually.

• The second option would be to add your Windows host IP to /etc/hosts. If your Windows IP is static, then you could just add it manually to /etc/hosts and be done. If it's dynamic, then you might want to script it. You can retrieve it from inside WSL2 via:

  powershell.exe "(Test-Connection -ComputerName (hostname) -Count 1).IPV4Address.IPAddressToString" (and other methods) and then use something like sed to change /etc/hosts.