Container orchestration in production in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker Swarm service command?

You run the command docker service ls in a Docker Swarm cluster. What output will you see if there are two services named webapp and db running with 3 and 1 replicas respectively?

Docker

docker service ls

A

ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
x1y2z3              webapp              replicated          3/3                 webapp:latest       *:80->80/tcp
x4y5z6              db                  replicated          1/1                 db:latest           

B

ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
x1y2z3              webapp              global              3/3                 webapp:latest       *:80->80/tcp
x4y5z6              db                  replicated          1/1                 db:latest           

C

ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
x1y2z3              webapp              replicated          2/3                 webapp:latest       *:80->80/tcp
x4y5z6              db                  replicated          1/1                 db:latest           

D

ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
x1y2z3              webapp              replicated          3/3                 webapp:latest       
x4y5z6              db                  replicated          1/1                 db:latest           

💡 Hint

Look carefully at the MODE and REPLICAS columns for each service.

The docker service ls command lists all services in the swarm. The webapp service is running in replicated mode with 3 replicas, so REPLICAS shows 3/3. The db service is also replicated with 1 replica. Option A correctly shows this state.

🧠 Conceptual

intermediate

Which orchestration feature ensures your app keeps running even if a node fails?

In container orchestration, what feature helps maintain application availability when a physical or virtual machine hosting containers crashes?

A Load balancing

B Image caching

C Service discovery

D Self-healing

💡 Hint

Think about automatic recovery without manual intervention.

Self-healing means the orchestrator detects failed containers or nodes and automatically restarts or reschedules containers to keep the app running.

❓ Configuration

advanced

Identify the correct Docker Compose snippet for scaling a service

Which Docker Compose YAML snippet correctly configures the web service to run 5 replicas in a production swarm?

A

version: '3.8'
services:
  web:
    image: myapp:latest
    replicas: 5
    restart_policy:
      condition: on-failure

B

version: '3.8'
services:
  web:
    image: myapp:latest
    deploy:
      replicas: 5
      restart_policy:
        condition: on-failure

C

version: '3.8'
services:
  web:
    image: myapp:latest
    deploy:
      mode: global
      replicas: 5

D

version: '3.8'
services:
  web:
    image: myapp:latest
    deploy:
      replicas: '5'
      restart_policy:
        condition: any

💡 Hint

Replicas must be under deploy and be a number, not a string.

In Docker Compose for swarm mode, scaling is set under deploy.replicas as a number. Option B correctly uses this syntax and a valid restart policy.

❓ Troubleshoot

advanced

Why does this Kubernetes pod stay in Pending state?

You deployed a pod with this YAML snippet but it stays in Pending state indefinitely. What is the most likely cause?

apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
  - name: test-container
    image: nginx
  nodeSelector:
    disktype: ssd

A No nodes in the cluster have the label <code>disktype=ssd</code>

B The image <code>nginx</code> is not available in the registry

C The pod spec is missing resource limits

D The pod name is invalid

💡 Hint

Check if the node labels match the pod's nodeSelector.

If no nodes have the label disktype=ssd, the scheduler cannot place the pod, so it stays Pending.

🔀 Workflow

expert

Order the steps to safely update a production Kubernetes deployment with zero downtime

Arrange these steps in the correct order to perform a rolling update on a Kubernetes deployment ensuring zero downtime.

A 1,2,4,3

B 2,1,3,4

C 1,2,3,4

D 1,3,2,4

💡 Hint

Think about editing first, then applying, then monitoring, then verifying.

First update the manifest, then apply it to the cluster. Next, monitor the rollout to ensure pods update correctly. Finally, verify the new pods serve traffic without downtime.