Container orchestration in production in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all running Docker containers.

Docker

docker [1]

Drag options to blanks, or click blank then click option'

Aps

Brun

Cstart

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker run' instead of 'docker ps' to list containers.

Using 'docker start' which starts a stopped container but does not list them.

The docker ps command lists all running containers.

2fill in blank

medium

Complete the command to create a Docker Swarm cluster on the current machine.

Docker

docker swarm [1]

Drag options to blanks, or click blank then click option'

Ajoin

Binit

Cleave

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'join' which is for adding nodes to an existing swarm.

Using 'leave' which removes a node from a swarm.

The docker swarm init command initializes a new swarm cluster on the current machine.

3fill in blank

hard

Fix the error in the command to deploy a service named 'web' with 3 replicas.

Docker

docker service create --name web --replicas [1] nginx

Drag options to blanks, or click blank then click option'

A3

B-3

Ctwo

Dzero

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'two' or 'zero' instead of numbers.

Using negative numbers like '-3' which are invalid.

The replicas option requires a positive integer. '3' is correct.

4fill in blank

hard

Fill both blanks to create a Docker Compose file snippet that defines a service named 'app' using the image 'myapp:latest'.

Docker

services:
  app:
    image: [1]
    [2]: 80

Drag options to blanks, or click blank then click option'

Amyapp:latest

Bports

Cvolumes

Denvironment

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'volumes' or 'environment' instead of 'ports' to expose ports.

Incorrect image name or format.

The image is 'myapp:latest' and 'ports' maps container port 80 to the host.

5fill in blank

hard

Fill all three blanks to write a Docker command that updates the 'web' service to use 5 replicas and the image 'nginx:stable'.

Docker

docker service update --replicas [1] --image [2] [3]

Drag options to blanks, or click blank then click option'

Aweb

Bnginx:stable

C5

Dmyapp

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of arguments.

Using wrong image or service names.

Set replicas to 5, image to 'nginx:stable', and specify the service name 'web'.

Practice

1. What is the main purpose of container orchestration in production environments?

easy

A. To manage and automate deployment, scaling, and operation of multiple containers

B. To write code inside containers

C. To create container images manually

D. To monitor CPU usage on a single container

Solution

1. Step 1: Understand container orchestration role

   Container orchestration automates managing many containers, including deployment and scaling.

2. Step 2: Compare options

   Only To manage and automate deployment, scaling, and operation of multiple containers describes managing and automating container groups, which is orchestration's goal.

3. Final Answer:

   To manage and automate deployment, scaling, and operation of multiple containers -> Option A

4. Quick Check:

   Orchestration = Manage & automate containers [OK]

Hint: Orchestration means managing many containers automatically [OK]

Common Mistakes:

• Confusing orchestration with coding inside containers
• Thinking orchestration is about creating images manually
• Believing orchestration only monitors single container stats

2. Which Docker Swarm command is used to create a new service in a cluster?

easy

A. docker service create

B. docker container run

C. docker swarm init

D. docker network create

Solution

1. Step 1: Identify command for creating services

   The command docker service create is used to start a new service in Docker Swarm.

2. Step 2: Eliminate other commands

   docker container run runs containers but not as a managed service; docker swarm init initializes the swarm; docker network create creates networks.

3. Final Answer:

   docker service create -> Option A

4. Quick Check:

   Service creation = docker service create [OK]

Hint: Service creation uses 'docker service create' command [OK]

Common Mistakes:

• Using 'docker container run' to create services
• Confusing swarm initialization with service creation
• Mixing network commands with service commands

3. What will be the output of the command docker service ls in a Docker Swarm cluster?

medium

A. List of all running containers on the host

B. List of all services running in the swarm with their replicas

C. List of all Docker images available locally

D. List of all networks created in Docker

Solution

1. Step 1: Understand the command purpose

   docker service ls shows all services in the swarm, including how many replicas each has.

2. Step 2: Compare with other options

   It lists services and replicas, not individual containers (<code>docker ps</code>), images (<code>docker images</code>), or networks (<code>docker network ls</code>).

3. Final Answer:

   List of all services running in the swarm with their replicas -> Option B

4. Quick Check:

   docker service ls = list swarm services [OK]

Hint: 'docker service ls' lists swarm services, not containers [OK]

Common Mistakes:

• Thinking it lists individual containers
• Confusing services with images or networks
• Expecting detailed container logs from this command

4. You run docker service scale myservice=5 but only 3 containers start. What is the likely cause?

medium

A. The command syntax is wrong

B. The service name is incorrect

C. Docker daemon is not running

D. Not enough resources on swarm nodes to run 5 replicas

Solution

1. Step 1: Analyze the scaling command

   The command syntax is correct and service name is assumed valid since some containers started.

2. Step 2: Identify resource constraints

   If only 3 replicas run instead of 5, likely the swarm nodes lack enough CPU/memory to start all replicas.

3. Final Answer:

   Not enough resources on swarm nodes to run 5 replicas -> Option D

4. Quick Check:

   Scaling fails due to resource limits [OK]

Hint: Scaling fails if swarm nodes lack resources [OK]

Common Mistakes:

• Assuming command syntax is wrong
• Thinking service name is invalid if some replicas run
• Ignoring resource limits on nodes

5. In a production Docker Swarm, how can you ensure your service stays running even if a node fails?

hard

A. Use 'docker container run' repeatedly on the same node

B. Run the service with a single replica on one node only

C. Set the service replicas to more than one so tasks run on multiple nodes

D. Disable swarm mode to avoid node failures

Solution

1. Step 1: Understand high availability in swarm

   Running multiple replicas spreads tasks across nodes, so if one node fails, others keep running the service.

2. Step 2: Evaluate options

   Single replica or running containers manually does not provide failover. Disabling swarm removes orchestration benefits.

3. Final Answer:

   Set the service replicas to more than one so tasks run on multiple nodes -> Option C

4. Quick Check:

   Multiple replicas = high availability [OK]

Hint: Use multiple replicas for failover in swarm [OK]

Common Mistakes:

• Running only one replica expecting failover
• Manually running containers without orchestration
• Disabling swarm mode to fix node failures