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ateom-microvm: give the micro-VM guest DNS so name-based egress works #1

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ateom-microvm: give the micro-VM guest DNS so name-based egress works #1

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34 changes: 34 additions & 0 deletions cmd/ateom-microvm/run.go
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,11 @@ func (s *AteomService) RunWorkload(ctx context.Context, req *ateompb.RunWorkload
}
tmpPath := tmp.Name()
_ = tmp.Close()
if err := writeGuestResolvConf(filepath.Join(bundle, "rootfs")); err != nil {
buildCancel()
_ = os.Remove(tmpPath)
return nil, fmt.Errorf("while writing guest resolv.conf: %w", err)
}
if err := kata.BuildExt4Image(buildCtx, filepath.Join(bundle, "rootfs"), tmpPath); err != nil {
buildCancel()
_ = os.Remove(tmpPath)
Expand Down Expand Up @@ -588,6 +593,32 @@ func ensureKataCompatibleSpec(bundle, id, netnsPath string) (*specs.Spec, error)
return &spec, nil
}

// writeGuestResolvConf gives the micro-VM guest working DNS by writing
// /etc/resolv.conf into the bundle rootfs before it is packed into the ext4
// disk. ateom drops atelet's /etc/resolv.conf bind (a host bind is meaningless
// inside a VM) and does not send CreateSandbox.Dns, so without this the guest
// can reach IP literals but cannot resolve names. We copy the worker pod's own
// resolv.conf (cluster DNS) verbatim -- the same source the kata shim's getDNS
// uses -- so the guest resolves both cluster and external names (e.g. ollama.com)
// out over the pod's NAT'd egress. Writing the file also satisfies the kata
// agent's requirement that /etc/resolv.conf already exist before it populates DNS.
func writeGuestResolvConf(rootfs string) error {
content, err := os.ReadFile("/etc/resolv.conf")
if err != nil || len(strings.TrimSpace(string(content))) == 0 {
// The worker pod always has a resolv.conf; this guard only trips in a
// degenerate environment, so the guest is never left without a resolver.
content = []byte("nameserver 1.1.1.1\nnameserver 8.8.8.8\n")
}
etc := filepath.Join(rootfs, "etc")
if err := os.MkdirAll(etc, 0o755); err != nil {
return fmt.Errorf("creating %q: %w", etc, err)
}
if err := os.WriteFile(filepath.Join(etc, "resolv.conf"), content, 0o644); err != nil {
return fmt.Errorf("writing guest resolv.conf: %w", err)
}
return nil
}

// defaultKataMounts mirrors the mount set `ctr run --runtime io.containerd.kata.v2`
// produces (the proven-good shape for the kata agent).
func defaultKataMounts() []specs.Mount {
Expand Down Expand Up @@ -888,6 +919,9 @@ func (s *AteomService) RestoreWorkload(ctx context.Context, req *ateompb.Restore
slog.InfoContext(ctx, "Reset actor rootfs disk to golden (template)", slog.String("id", id))
} else {
bundleRootfs := filepath.Join(ateompath.OCIBundlePath(ns, name, id, containers[0].GetName()), "rootfs")
if err := writeGuestResolvConf(bundleRootfs); err != nil {
return nil, fmt.Errorf("while writing guest resolv.conf: %w", err)
}
// Detach from the resume RPC deadline: reconstructing a multi-GB rootfs via
// mkfs.ext4 -d can take minutes and would otherwise be SIGKILLed mid-write.
// (Unlike the golden boot this is reset-each-restore, so it always rebuilds.)
Expand Down
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