Container networking in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is container networking?

Container networking is the way containers communicate with each other and with the outside world. It connects containers so they can share data and services.

intermediate

Name a common network model used in container orchestration platforms like Kubernetes.

The common network model is the "flat network" where every container gets its own IP address and can communicate directly with others without NAT (Network Address Translation).

intermediate

What is a network namespace in container networking?

A network namespace isolates the network stack for a container. It means each container can have its own IP addresses, routing tables, and ports, separate from the host or other containers.

advanced

Explain the role of a Container Network Interface (CNI).

CNI is a set of standards and plugins that help connect containers to networks. It manages IP address allocation and network setup for containers in a consistent way.

advanced

What is the difference between bridge and overlay networks in container networking?

Bridge networks connect containers on the same host, like a local switch. Overlay networks connect containers across multiple hosts, creating a virtual network over the physical one.

Which of the following best describes a network namespace?

A A physical network switch

B An isolated network environment for a container

C A type of container image

D A storage volume for containers

A network namespace isolates the network stack for a container, giving it its own IP and ports.

What does CNI stand for in container networking?

A Container Network Isolation

B Container Node Integration

C Container Network Interface

D Cloud Network Infrastructure

CNI stands for Container Network Interface, a standard for configuring container networks.

Which network type connects containers across multiple hosts?

A Overlay network

B Host network

C Bridge network

D Loopback network

Overlay networks create a virtual network over physical networks to connect containers on different hosts.

In Kubernetes, how do containers typically communicate within a pod?

A Using separate IP addresses

B Through external load balancer

C Via host network only

D Using shared network namespace

Containers in the same pod share the same network namespace, allowing them to communicate via localhost.

What is the main purpose of a bridge network in container environments?

A Connect containers on the same host

B Connect containers across different hosts

C Provide internet access to containers

D Isolate containers from the host

Bridge networks connect containers on the same host, acting like a virtual switch.

Describe how container networking allows containers to communicate within the same host and across multiple hosts.

Think about local vs virtual networks and how IP addresses are assigned.

Explain the concept of network namespaces and why they are important in container networking.

Imagine each container having its own private network space.

Practice

1. What is the main purpose of container networking in microservices?

easy

A. To allow containers to communicate with each other

B. To store container data persistently

C. To build user interfaces for containers

D. To monitor container CPU usage

Solution

1. Step 1: Understand container networking role

   Container networking connects containers so they can send data and messages to each other.

2. Step 2: Compare with other options

   Storing data, building interfaces, and monitoring CPU are not related to networking.

3. Final Answer:

   To allow containers to communicate with each other -> Option A

4. Quick Check:

   Container networking = communication [OK]

Hint: Networking means communication between containers [OK]

Common Mistakes:

• Confusing networking with storage
• Thinking networking builds UI
• Mixing monitoring with networking

2. Which Docker command creates a user-defined network named mynet?

easy

A. docker create network mynet

B. docker network create mynet

C. docker network new mynet

D. docker net create mynet

Solution

1. Step 1: Recall Docker network creation syntax

   The correct command is docker network create <name>.

2. Step 2: Match options with syntax

   Only docker network create mynet matches the correct syntax exactly.

3. Final Answer:

   docker network create mynet -> Option B

4. Quick Check:

   docker network create = correct syntax [OK]

Hint: Remember: 'docker network create' is the right command [OK]

Common Mistakes:

• Swapping 'create' and 'network' order
• Using 'new' instead of 'create'
• Shortening 'network' to 'net' incorrectly

3. Given two containers web and db connected on a user-defined network mynet, what happens when web tries to ping db by container name?

medium

A. Ping succeeds because containers can resolve names on the same user-defined network

B. Ping fails because container names are not resolvable

C. Ping succeeds only if IP addresses are used, not names

D. Ping fails because containers cannot communicate on user-defined networks

Solution

1. Step 1: Understand user-defined network DNS resolution

   User-defined Docker networks provide automatic DNS resolution of container names.

2. Step 2: Apply to ping scenario

   Since both containers are on mynet, web can ping db by name successfully.

3. Final Answer:

   Ping succeeds because containers can resolve names on the same user-defined network -> Option A

4. Quick Check:

   User-defined network = name resolution works [OK]

Hint: User-defined networks enable container name resolution [OK]

Common Mistakes:

• Assuming container names are never resolvable
• Thinking IP addresses are always required
• Believing user-defined networks block communication

4. You created two containers on the default bridge network but they cannot communicate by container name. What is the likely cause?

medium

A. Container names must be IP addresses on default bridge

B. Containers must be on different networks to communicate

C. Default bridge network does not support automatic container name resolution

D. Docker daemon is not running

Solution

1. Step 1: Recall default bridge network limitations

   The default bridge network does not provide automatic DNS for container names.

2. Step 2: Analyze communication failure

   Without name resolution, containers cannot reach each other by name on default bridge.

3. Final Answer:

   Default bridge network does not support automatic container name resolution -> Option C

4. Quick Check:

   Default bridge = no name resolution [OK]

Hint: Default bridge lacks container name DNS [OK]

Common Mistakes:

• Thinking containers must be on different networks to communicate
• Confusing container names with IP addresses
• Assuming Docker daemon is stopped without checking

5. You want to isolate microservices into separate networks for security but allow only the api service to communicate with db. Which design best achieves this?

hard

A. Create separate networks but connect all containers to all networks.

B. Connect all services to a single network and use firewall rules inside containers.

C. Use the default bridge network for all containers and rely on container names.

D. Create two networks: api-net and db-net. Connect api to both networks, db only to db-net.

Solution

1. Step 1: Understand network isolation and selective communication

   Separating services into different networks isolates traffic. Connecting api to both networks allows it to talk to db while others cannot.

2. Step 2: Evaluate options for security and communication

   Create two networks: api-net and db-net. Connect api to both networks, db only to db-net. isolates db and allows only api access. Other options either lack isolation or allow unwanted access.

3. Final Answer:

   Create two networks: api-net and db-net. Connect api to both networks, db only to db-net. -> Option D

4. Quick Check:

   Separate networks + selective connection = secure communication [OK]

Hint: Use multiple networks and connect only needed containers [OK]

Common Mistakes:

• Putting all containers on one network without isolation
• Connecting all containers to all networks
• Relying on default bridge network for security