Overriding DNS in Kubernetes Pods: Hosts, HostAliases, CoreDNS & Custom Strategies

In this article we examine several ways to control domain name resolution inside Kubernetes containers, starting with a sample Deployment that runs a busybox pod printing "Hello, Kubernetes!" every 10 seconds.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: busybox-deployment
  labels:
    app: busybox
spec:
  replicas: 1
  selector:
    matchLabels:
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      containers:
      - name: busybox
        image: busybox
        args:
        - /bin/sh
        - -c
        - "while true; do echo Hello, Kubernetes!; sleep 10;done"

TL;DR

Modify /etc/hosts – pod level – not recommended for production.

Add HostAliases – pod/Deployment/StatefulSet level – recommended.

Change CoreDNS configuration – cluster‑wide – recommended.

Custom DNS policy – pod/Deployment/StatefulSet level – use as needed.

Third‑party DNS plugin – cluster‑wide – not recommended.

Modify /etc/hosts

Editing /etc/hosts inside a container is the most traditional method; it works at the pod level but requires manual changes after each restart, making it unsuitable for production.

250.250.250.250 four-250

Add HostAliases

The hostAliases field in a Pod spec adds extra entries to the pod's /etc/hosts file, useful for overriding or adding hostnames.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: busybox-deployment
  labels:
    app: busybox
spec:
  replicas: 3
  selector:
    matchLabels:
      app: busybox
  template:
    metadata:
      labels:
        app: busybox
    spec:
      hostAliases:
      - ip: "250.250.250.250"
        hostnames:
        - "four-250"
      containers:
      - name: busybox
        image: busybox
        args:
        - /bin/sh
        - -c
        - "while true; do echo Hello, Kubernetes!; sleep 10;done"

Kubernetes automatically inserts a comment "# Entries added by HostAliases" into the generated /etc/hosts file.

func hostsEntriesFromHostAliases(hostAliases []v1.HostAlias) []byte {
    if len(hostAliases) == 0 {
        return []byte{}
    }
    var buffer bytes.Buffer
    buffer.WriteString("
")
    buffer.WriteString("# Entries added by HostAliases.
")
    for _, hostAlias := range hostAliases {
        buffer.WriteString(fmt.Sprintf("%s\t%s
", hostAlias.IP, strings.Join(hostAlias.Hostnames, "\t")))
    }
    return buffer.Bytes()
}

CoreDNS configuration

Modifying the CoreDNS ConfigMap allows cluster‑wide custom DNS entries.

Command: kubectl edit cm coredns -n kube-system Original Corefile snippet:

Corefile: |
    .:53 {
        log
        errors
        health {
           lameduck 5s
        }
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
           ttl 30
        }
        prometheus :9153
        hosts {
           192.168.65.2 host.minikube.internal
           fallthrough
        }
        forward . /etc/resolv.conf {
           max_concurrent 1000
        }
        cache 30
        loop
        reload
        loadbalance
    }

Add a custom host entry: 250.250.250.250 four-250 If the reload plugin is not enabled, CoreDNS must be restarted; the default reload interval is 30 seconds.

Custom DNS policy

By setting dnsConfig in the pod spec you can direct specific DNS queries to chosen nameservers and search domains.

spec:
  dnsConfig:
    nameservers:
    - 1.2.3.4
    searches:
    - search.prefix
  containers:
  - name: busybox
    image: busybox
    args:
    - /bin/sh
    - -c
    - "while true; do echo Hello, Kubernetes!; sleep 10;done"

Third‑party DNS plugin

Using alternative DNS plugins is not recommended because CoreDNS is the industry‑standard and lacks a mature replacement.

Reference: https://www.cnblogs.com/huaweiyun/p/17903421.html