macos-latest lacking localhost

[bje-]

Description

The macos-latest runner was failing on some Python tests I had written that made use of a simple TCP client and server. To confirm my suspicions, I added a host localhost command to one of my install dependencies step and sure enough I got:

Host localhost not found: 3(NXDOMAIN)

Why doesn't the runner have an /etc/hosts or similar entry for localhost?

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 18.04
• Ubuntu 20.04
• Ubuntu 22.04
• macOS 10.15
• macOS 11
• macOS 12
• Windows Server 2019
• Windows Server 2022

Image version and build link

Image: macos-11
Version: 20221002.2

Is it regression?

Unsure

Expected behavior

I expect localhost to be defined as it is on ubuntu-latest.

Actual behavior

localhost is not found, so tests that refer to this hostname fail.

Repro steps

Create a build script that runs host localhost to reproduce.

[al-cheb]

Hey @bje-.
This is by design. The host command uses standard C library calls to contact the DNS resolvers directory; it does not use mDNSResponder or DirectoryService(bypass the system name resolver, and query DNS directly, it won't resolve names defined in /etc/hosts (unless they're also defined in the DNS service)).

To resolve ip address for host entry in /etc/hosts, you should use dscacheutil -q host -a name localhost command:

The default DNS on macOS is set to 8.8.8.8 without localhost defined entries in it. But for test purposes you could use - 9.9.9.9:

 - run: host localhost || true
 - run: sudo networksetup -setdnsservers Ethernet 9.9.9.9
 - run: host localhost

[bje-]

OK, my choice of using host to demonstrate the problem was not the greatest idea. I'm simply trying to illustrate that localhost is not a recognised hostname for applications being tested on the macos-latest runner. It doesn't strike me as unusual to expect it to be.

I'll use your workaround for now. Thanks.

[lastmjs]

Can we get this issue fixed? It seems strange that localhost simply doesn't work on MacOS. I have test code that is identical running on Ubuntu runners, and switching to MacOS runners are tests simply started failing in a very confusing way.