CODEWITHSUNDEEP
kubernetesdnsjvmminikubecoredns
Matjaž
Matjaž

Reputation: 2115

Minikube's CoreDNS fails to resolve names from JVM

Our JVM services (based on Java SE 8/Scala/Finagle) have problems resolving DNS names. I have checked coredns deployment logs in kube-system namespace and found out that java.net.InetAddress.getAllByName() is querying for ANY record type.

If I check name resolution via nslookup I can confirm that ANY record type is not resolvable, but A or AAAA records are:

# kubectl exec -i -t dnsutils -- nslookup -type=a weather.mab.matjazmav.test
Server:         10.96.0.10
Address:        10.96.0.10#53

Name:   dev-proxy.default.svc.cluster.local
Address: 10.100.187.185

# kubectl exec -i -t dnsutils -- nslookup -type=any weather.mab.matjazmav.test
Server:         10.96.0.10
Address:        10.96.0.10#53

*** Can't find weather.mab.matjazmav.test: No answer

My question is, how can I make Minikube's CoreDNS respond to ANY query, or how can I force java.net.InetAddress to send A or AAAA query?

EDIT: It turned out that we used old NS provider that ships with Java SE 8 (sun.net.spi.nameservice.provider.1=dns,sun) see my answer for details.

Upvotes: 2

Views: 540

Answers (1)

Matjaž
Matjaž

Reputation: 2115

I found two possible solutions:

1. Use CoreDNS rewrite plugin

Rewrite query types from ANY to A. Here is a link to the documentation: https://coredns.io/plugins/rewrite/

2. Use default NS provider inside JVM

This applies only if you run on Jave SE 8 or older. Java SE 9 removed this system property, read more here: https://www.oracle.com/java/technologies/javase/9-removed-features.html#JDK-8134577

Java SE 8 ships with two NS providers default and dns,sun. default provider uses system's NS provider while dns,sun uses some old NS implementation.

To use default NS provider simply set the following property:

sun.net.spi.nameservice.provider.1=default

Read more here: https://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html

Also this is a nice read: https://medium.com/@maheshsenni/host-name-resolution-in-java-80301fea465a

Upvotes: 2

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