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Fix DNS resolution in ephemeral guests #167

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Fix DNS resolution in ephemeral guests #167

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@gursewak1997 gursewak1997 commented Dec 1, 2025

Configure QEMU user-mode networking to use host DNS servers from /etc/resolv.conf instead of the default 10.0.2.3, which doesn't work when QEMU runs inside containers.

@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch 2 times, most recently from d5e8558 to f693004 Compare December 2, 2025 06:26
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I'm fine with this overall if you are; a few nits.

That said, an integration test (run as part of just test-integration ephemeral) would be both easy and IMO mandatory for changes like this.

@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch 8 times, most recently from 542253f to 8b859ad Compare December 2, 2025 23:18
@gursewak1997 gursewak1997 marked this pull request as ready for review December 3, 2025 01:25
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cgwalters reviewed Dec 3, 2025
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@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch 3 times, most recently from dcc3ad4 to 9996db4 Compare December 5, 2025 19:52
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gursewak1997 commented Dec 5, 2025 •
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Network connectivity test (podman pull) failed: stdout: Error: configure storage: 'overlay' is not supported over overlayfs, a mount_program is required: backing file system is unsupported for this graph driver
Can switch to something simpler which doesn't require podman
Edit: Switching the test to use HTTP

@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch from 9996db4 to 5e28fd5 Compare December 5, 2025 21:31
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cgwalters commented Dec 5, 2025 •
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Error: configure storage: 'overlay' is not supported over overlayfs, a mount_program is required: backing file system is unsupported for this graph driver

Ah yes that relates to #22 - basically all of /var needs to be equivalent to a VOLUME in docker/podman terms - it needs to be copied up to a tmpfs.

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One nit otherwise looks sane (though I'd reiterate we probably really do want a bigger fix of --net=host per the issue, but this helps for now)

crates/integration-tests/src/tests/run_ephemeral_ssh.rs
"-c",
r#"
for i in $(seq 1 30); do
ip -4 addr show | grep -q "inet " && break
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Because ssh requires IP networking, I can't think of a scenario in which ssh would work but this could somehow fail. This is likely just dead code.

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I see. Updated and removed the dead code there.

@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch from 5e28fd5 to 57af585 Compare December 5, 2025 21:52
@gursewak1997 gursewak1997 linked an issue Dec 5, 2025 that may be closed by this pull request
DNS resolving not working in ephemeral guests #123
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@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch from 57af585 to eb89500 Compare December 6, 2025 08:00
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gursewak1997 commented Dec 9, 2025

Reworking this PR as I think it will require a few more changes.

@cgwalters cgwalters marked this pull request as draft December 10, 2025 17:35
@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch from eb89500 to 5cf80aa Compare December 10, 2025 18:59
@gursewak1997
Fix DNS resolution in ephemeral guests
3bf0686 
QEMU's slirp reads /etc/resolv.conf from the container namespace,
which contains unreachable bridge DNS servers. On systemd-resolved
hosts, it only has 127.0.0.53 (stub resolver).

Read upstream DNS servers from host's /run/systemd/resolve/resolv.conf,
pass them to the container, and write /etc/resolv.conf before starting QEMU.

Signed-off-by: gursewak1997 <[email protected]>
@gursewak1997 gursewak1997 force-pushed the fix/dns-resolution-ephemeral-guests branch from 5cf80aa to 3bf0686 Compare December 10, 2025 22:25
@gursewak1997 gursewak1997 marked this pull request as ready for review December 10, 2025 23:04
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DNS resolving not working in ephemeral guests

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