I custom the k8s core dns file to resolve a custom name.which works fine in pods checked by ping xx. But it not resolved in java appliation(jdk14). Nameserver is ok.
/ # cat /etc/resolv.conf
nameserver 10.96.0.10
search xxxx-5-production.svc.cluster.local svc.cluster.local cluster.local
/ # ping xx
PING xx (192.168.65.2): 56 data bytes
64 bytes from 192.168.65.2: seq=0 ttl=37 time=0.787 msEdit: I use coredns rewrite host name xx to host.docker.internal,this is change to coredns config
rewrite name regex (^|(?:\S*\.)*)xx\.?$ {1}host.docker.internalI add some debug code to the entry:
static void runCommand(String... commands) {
try {
ProcessBuilder cat = new ProcessBuilder(commands);
Process start = cat.start();
start.waitFor();
String output = new BufferedReader(new InputStreamReader(start.getInputStream())).lines().collect(Collectors.joining());
String err = new BufferedReader(new InputStreamReader(start.getErrorStream())).lines().collect(Collectors.joining());
log.info("\n{}: stout {}", Arrays.toString(commands),output);
log.info("\n{}: sterr{}", Arrays.toString(commands),err);
} catch (IOException | InterruptedException e) {
log.error(e.getClass().getCanonicalName(), e);
}
}
public static void main(String[] args) {
try {
InetAddress xx = Inet4Address.getByName("xx");
log.info("{}: {}", "InetAddress xx", xx.getHostAddress());
} catch (IOException e) {
log.error(e.getClass().getCanonicalName(), e);
}
runCommand("cat", "/etc/resolv.conf");
runCommand("ping", "xx","-c","1");
runCommand("ping", "host.docker.internal","-c","1");
runCommand("nslookup", "xx");
runCommand("ifconfig");
SpringApplication.run(FileServerApp.class, args);
}
Here is output:
01:01:39.950 [main] ERROR com.j.file_server_app.FileServerApp - java.net.UnknownHostException
java.net.UnknownHostException: xx: Name or service not known
at java.base/java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:932)
at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1505)
at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:851)
at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1495)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1354)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1288)
at java.base/java.net.InetAddress.getByName(InetAddress.java:1238)
at com.j.file_server_app.FileServerApp.main(FileServerApp.java:43)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:87)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:51)
at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:52)
01:01:39.983 [main] INFO com.j.file_server_app.FileServerApp -
[cat, /etc/resolv.conf]: stout nameserver 10.96.0.10search default.svc.cluster.local svc.cluster.local cluster.localoptions ndots:5
01:01:39.985 [main] INFO com.j.file_server_app.FileServerApp -
[cat, /etc/resolv.conf]: sterr
01:01:39.991 [main] INFO com.j.file_server_app.FileServerApp -
[ping, xx, -c, 1]: stout
01:01:39.991 [main] INFO com.j.file_server_app.FileServerApp -
[ping, xx, -c, 1]: sterrping: unknown host
01:01:39.998 [main] INFO com.j.file_server_app.FileServerApp -
[ping, host.docker.internal, -c, 1]: stout PING host.docker.internal (192.168.65.2): 56 data bytes64 bytes from 192.168.65.2: icmp_seq=0 ttl=37 time=0.757 ms--- host.docker.internal ping statistics ---1 packets transmitted, 1 packets received, 0% packet lossround-trip min/avg/max/stddev = 0.757/0.757/0.757/0.000 ms
01:01:39.998 [main] INFO com.j.file_server_app.FileServerApp -
[ping, host.docker.internal, -c, 1]: sterr
01:01:40.045 [main] INFO com.j.file_server_app.FileServerApp -
[nslookup, xx]: stout Server: 10.96.0.10Address: 10.96.0.10#53Non-authoritative answer:Name: host.docker.internalAddress: 192.168.65.2** server can't find xx: NXDOMAIN
01:01:40.045 [main] INFO com.j.file_server_app.FileServerApp -
[nslookup, xx]: sterr
01:01:40.048 [main] INFO com.j.file_server_app.FileServerApp -
[ifconfig]: stout eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 10.1.3.14 netmask 255.255.0.0 broadcast 0.0.0.0 ether ce:71:60:9a:75:05 txqueuelen 0 (Ethernet) RX packets 35 bytes 3776 (3.6 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 22 bytes 1650 (1.6 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 loop txqueuelen 1000 (Local Loopback) RX packets 1 bytes 29 (29.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 1 bytes 29 (29.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
01:01:40.048 [main] INFO com.j.file_server_app.FileServerApp -
[ifconfig]: sterrLooks like coredns not working,but in the front end pod,ping is ok,this is front end Dockerfile
FROM library/nginx:stable-alpine
RUN mkdir /app
EXPOSE 80
ADD dist /app
COPY nginx.conf /etc/nginx/nginx.confUsing docker inspect for fontend and backend container,both network setting are:
"NetworkSettings": {
"Bridge": "",
"SandboxID": "",
"HairpinMode": false,
"LinkLocalIPv6Address": "",
"LinkLocalIPv6PrefixLen": 0,
"Ports": {},
"SandboxKey": "",
"SecondaryIPAddresses": null,
"SecondaryIPv6Addresses": null,
"EndpointID": "",
"Gateway": "",
"GlobalIPv6Address": "",
"GlobalIPv6PrefixLen": 0,
"IPAddress": "",
"IPPrefixLen": 0,
"IPv6Gateway": "",
"MacAddress": "",
"Networks": {}
}
Both frontend and backend has service with type: LoadBalancer,now my question is why the name resolve behave different in this two pods?