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Docker & Kubernetes for Developers · Aula

Descoberta de serviços e DNS no K8s

Explore como o Kubernetes gerencia a descoberta de serviços e a resolução de DNS na comunicação entre serviços.

Descoberta de serviços e DNS no K8s é uma aula grátis de Docker & Kubernetes for Developers no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Docker & Kubernetes for Developers, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Docker & Kubernetes for Developers inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Intro to Service Discovery

Welcome to Service Discovery & DNS in K8s! In a dynamic Kubernetes cluster, Pods are constantly created, destroyed, and moved, leading to ever-changing IP addresses.

How do applications running in one Pod find and communicate with applications in another Pod or Service?

This is where Service Discovery comes in. It's how services find each other without needing to know their specific, ephemeral IP addresses.

The Role of DNS in K8s

You might already know about DNS (Domain Name System) on the internet. It translates human-readable names like google.com into IP addresses.

Kubernetes uses a similar concept internally. Instead of relying on unstable Pod IPs, K8s assigns stable DNS names to its Services.

This allows your applications to connect to other services using simple, consistent names.

CoreDNS: The K8s DNS Server

Every Kubernetes cluster comes with its own DNS server, typically CoreDNS (or sometimes kube-dns in older versions).

CoreDNS runs as a Pod within your cluster and is responsible for resolving all internal Kubernetes service names to their corresponding cluster IP addresses.

It's automatically configured for you when you set up your cluster.

How Pods Get DNS Config

When a Pod starts, Kubernetes automatically injects DNS configuration into it.

  • Each Pod's /etc/resolv.conf file is updated to point to the cluster's CoreDNS Service IP.
  • It also includes search paths, allowing you to use shorter service names.

This means any application inside a Pod can immediately use the cluster's DNS for name resolution.

Service DNS Names

When you create a Kubernetes Service (e.g., a ClusterIP Service), CoreDNS automatically creates a DNS record for it.

The most common format for a Service's DNS name within its own namespace is simply: <service-name>.

For example, a service named my-web-app in the default namespace can be reached by other Pods in the same namespace using just my-web-app.

Example: Same-Namespace Access

Let's say you have a deployment hello-app and a service hello-service in the default namespace. Any other Pod in default can reach it via hello-service.

Here's a simple example of a Deployment and Service:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-app
spec:
  selector:
    matchLabels:
      app: hello
  replicas: 1
  template:
    metadata:
      labels:
        app: hello
    spec:
      containers:
      - name: hello-container
        image: busybox
        command: ["sh", "-c", "while true; do echo Hello K8s; sleep 5; done"]

---

apiVersion: v1
kind: Service
metadata:
  name: hello-service
spec:
  selector:
    app: hello
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
  type: ClusterIP

Testing Same-Namespace DNS

After applying the YAML from the previous scene, you can test service discovery. First, create a temporary Pod (e.g., debug-pod) in the same namespace.

Then, exec into debug-pod and try to ping the service:

  • kubectl run debug-pod --image=busybox --restart=Never --rm -it --command -- sh
  • Inside the pod: ping hello-service

You should see the hello-service ClusterIP being resolved!

Cross-Namespace DNS (FQDN)

What if your services are in different namespaces? Kubernetes uses a Fully Qualified Domain Name (FQDN) format:

<service-name>.<namespace-name>.svc.cluster.local

For convenience, if the Pod's namespace is in its DNS search path (which it usually is), you can often use a shorter form:

<service-name>.<namespace-name>

This allows clear and unambiguous communication across different parts of your application.

Example: Cross-Namespace Access

Let's imagine a backend-service in the prod namespace. From a Pod in the default namespace, you'd access it like this:

ping backend-service.prod

Kubernetes DNS handles the resolution, directing traffic to the correct service, even across namespaces.

This provides strong isolation while still enabling communication where needed.

Quick Check

Which of the following statements are TRUE regarding Kubernetes Service Discovery and DNS?

Recap: Service Discovery & DNS

Great job! In this lesson, you learned how Kubernetes handles service discovery and DNS resolution for internal communication:

  • Pods have ephemeral IPs, requiring a stable discovery mechanism.
  • CoreDNS is the cluster's internal DNS server.
  • Services get stable DNS names, resolvable by other Pods.
  • Pods are automatically configured to use the cluster's DNS.
  • You can access services in the same namespace by name or in other namespaces using FQDNs.

This powerful system ensures your applications can always find each other reliably!

Perguntas Frequentes

A aula “Descoberta de serviços e DNS no K8s” é grátis?

Sim — o texto completo de “Descoberta de serviços e DNS no K8s” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Docker & Kubernetes for Developers, atualize para CoddyKit PRO. O curso de Docker & Kubernetes for Developers inclui 4 aulas no total.

O que vou aprender em “Descoberta de serviços e DNS no K8s”?

Explore como o Kubernetes gerencia a descoberta de serviços e a resolução de DNS na comunicação entre serviços. Você pratica Docker & Kubernetes for Developers com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar Docker & Kubernetes for Developers?

Nenhuma experiência prévia é necessária. Docker & Kubernetes for Developers no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Descoberta de serviços e DNS no K8s”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de Docker & Kubernetes for Developers?

Sim. Cada aula de Docker & Kubernetes for Developers inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Ingress e roteamento no Kubernetes
  2. Implementação de políticas de rede
  3. Descoberta de serviços e DNS no K8s
  4. Encerramento de TLS e proteção do Ingress com HTTPS
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