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Document Pods using FQDN based policies must respect DNS TTL #6230

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Apr 17, 2024
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Document Pods using FQDN based policies must respect DNS TTL #6230

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7 changes: 7 additions & 0 deletions docs/antrea-network-policy.md
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Expand Up @@ -1366,6 +1366,13 @@ Antrea will only program datapath rules for actual egress traffic towards these
on DNS results. It will not interfere with DNS packets, unless there is a separate policy
dropping/rejecting communication between the DNS components and the Pods selected.

Antrea respects the TTL of DNS records, expiring stale IPs that are absent in more recent
records according to their TTL. Therefore, Pods employing FQDN based policies ought to refrain
from caching a DNS record for a duration exceeding its TTL. Otherwise, FQDN based policies may
intermittently fail to function as intended. Typically, the Java virtual machine (JVM) caches
DNS records for a fixed period of time, controlled by `networkaddress.cache.ttl`. In this
case, it’s crucial to set the JVM’s TTL to 0 so that FQDN based policies can work properly.

Note that FQDN based policies do not work for [Service DNS names created by
Kubernetes](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#services)
(e.g. `kubernetes.default.svc` or `antrea.kube-system.svc`), except for headless
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