Container DNS and service discovery in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is service discovery in container environments?

Service discovery is the process that allows containers to find and communicate with each other automatically without hardcoding IP addresses.

beginner

How does Docker's embedded DNS server help containers communicate?

Docker provides an embedded DNS server that resolves container names to their IP addresses within a user-defined network, enabling containers to reach each other by name.

intermediate

What is the role of Docker networks in service discovery?

Docker networks isolate containers and provide DNS-based service discovery so containers on the same network can find each other by container name.

intermediate

Explain how to use container names for service discovery in Docker Compose.

In Docker Compose, services can reach each other by using the service name as a hostname because Compose creates a default network with embedded DNS resolving service names.

intermediate

What happens if containers are not on the same Docker network regarding DNS resolution?

If containers are on different Docker networks, they cannot resolve each other's names via Docker's embedded DNS, so service discovery by name will fail unless external DNS or other methods are used.

What does Docker's embedded DNS server do?

A Manages container storage volumes

B Blocks network traffic between containers

C Assigns static IP addresses to containers

D Resolves container names to IP addresses within a Docker network

Docker's embedded DNS server resolves container names to their IP addresses within the same Docker network, enabling name-based communication.

How can containers communicate by name in Docker Compose?

A By using the service names as hostnames

B By using IP addresses only

C By configuring external DNS servers manually

D By sharing the same storage volume

Docker Compose creates a network where service names act as hostnames, allowing containers to communicate by those names.

What is required for Docker containers to resolve each other's names automatically?

A They must have static IP addresses

B They must use host networking mode

C They must be on the same Docker network

D They must run on the same physical host

Containers must be connected to the same Docker network to use Docker's embedded DNS for name resolution.

If two containers are on different Docker networks, what happens when one tries to resolve the other's name?

A The containers communicate through the host network

B The DNS resolution fails

C The containers share the same IP address

D The containers automatically connect

Docker's embedded DNS only resolves names within the same network, so cross-network name resolution fails.

Which Docker command creates a user-defined network that supports service discovery?

A docker network create my-network

B docker volume create my-network

C docker run --network=host

D docker build my-network

The command 'docker network create' creates a user-defined network where containers can discover each other by name.

Describe how Docker's embedded DNS and user-defined networks enable service discovery between containers.

Think about how containers find each other without hardcoded IPs.

Explain why service discovery might fail if containers are on different Docker networks and how to fix it.

Consider Docker's network isolation and DNS scope.