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Fix fallback DNS for IMDS and IPV6-only

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Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
This commit is contained in:
Brad Davidson
2025-07-31 22:09:08 +00:00
committed by Vitor Savian
parent cd3f2e321e
commit fa9e056bda
2 changed files with 22 additions and 5 deletions
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24
pkg/agent/config/config.go
View File

@@ -47,6 +47,8 @@ const (
DefaultPodManifestPath = "pod-manifests"
)
var InstanceMetadataServiceIP = net.ParseIP("169.254.169.254")
// Get returns a pointer to a completed Node configuration struct,
// containing a merging of the local CLI configuration with settings from the server.
// Node configuration includes client certificates, which requires node password verification,
@@ -390,8 +392,7 @@ func isValidResolvConf(resolvConfFile string) bool {
for scanner.Scan() {
ipMatch := nameserver.FindStringSubmatch(scanner.Text())
if len(ipMatch) == 2 {
ip := net.ParseIP(ipMatch[1])
if ip == nil || !ip.IsGlobalUnicast() {
if !isValidNameserver(ipMatch[1]) {
return false
} else {
foundNameserver = true
@@ -404,6 +405,21 @@ func isValidResolvConf(resolvConfFile string) bool {
return foundNameserver
}
// isValidNameserver returns a boolean indicating whether or not the IP is a valid
// upstream resolver address. Resolver IPs must be valid global unicast addresses, with
// the exception of the instance metadata service IP, which some cloud providers require
// traffic be forwarded to in order for private DNS to work properly.
func isValidNameserver(addr string) bool {
ip := net.ParseIP(addr)
if ip == nil {
return false
}
if !ip.IsGlobalUnicast() && !ip.Equal(InstanceMetadataServiceIP) {
return false
}
return true
}
func locateOrGenerateResolvConf(envInfo *cmds.Agent) string {
if envInfo.ResolvConf != "" {
return envInfo.ResolvConf
@@ -416,11 +432,11 @@ func locateOrGenerateResolvConf(envInfo *cmds.Agent) string {
}
resolvConf := filepath.Join(envInfo.DataDir, "agent", "etc", "resolv.conf")
if err := agentutil.WriteFile(resolvConf, "nameserver 8.8.8.8\n"); err != nil {
if err := agentutil.WriteFile(resolvConf, "nameserver 8.8.8.8\nnameserver 2001:4860:4860::8888\n"); err != nil {
logrus.Errorf("Failed to write %s: %v", resolvConf, err)
return ""
}
logrus.Warnf("Host resolv.conf includes loopback or multicast nameservers - kubelet will use autogenerated resolv.conf with nameserver 8.8.8.8")
logrus.Warnf("Host resolv.conf includes loopback, multicast, or link-local nameservers - kubelet will use autogenerated resolv.conf with nameservers 8.8.8.8 2001:4860:4860::8888")
return resolvConf
}

3
pkg/agent/config/config_internal_test.go
View File

@@ -13,9 +13,10 @@ func Test_isValidResolvConf(t *testing.T) {
}{
{name: "Valid ResolvConf", fileContent: "nameserver 8.8.8.8\nnameserver 2001:4860:4860::8888\n", expectedResult: true},
{name: "Invalid ResolvConf", fileContent: "nameserver 999.999.999.999\nnameserver not.an.ip\n", expectedResult: false},
{name: "Wrong Nameserver", fileContent: "search example.com\n", expectedResult: false},
{name: "No Nameserver", fileContent: "search example.com\n", expectedResult: false},
{name: "One valid nameserver", fileContent: "test test.com\nnameserver 8.8.8.8", expectedResult: true},
{name: "Non GlobalUnicast", fileContent: "nameserver ::1\nnameserver 169.254.0.1\nnameserver fe80::1\n", expectedResult: false},
{name: "Instance Metadata", fileContent: "nameserver 169.254.169.254", expectedResult: true},
{name: "Empty File", fileContent: "", expectedResult: false},
}