Manager and worker nodes in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Role of Manager Node in Docker Swarm

In a Docker Swarm cluster, what is the primary responsibility of a manager node?

A Scheduling tasks and managing cluster state

B Only running containers without managing the cluster

C Storing container images locally

D Providing network access to containers

💡 Hint

Think about which node controls the cluster and decides where containers run.

The manager node controls the swarm, schedules tasks, and manages cluster state. Worker nodes only run tasks assigned by managers.

💻 Command Output

intermediate

Output of 'docker node ls' on Manager Node

What is the expected output of the command docker node ls when run on a manager node in a Docker Swarm?

Docker

docker node ls

A Lists all nodes in the swarm with their status and roles

B Shows only the current node's status

C Returns an error if run on a worker node

D Displays running containers on the node

💡 Hint

Consider what information a manager node can access about the swarm.

The docker node ls command lists all nodes in the swarm with their roles and status.

🔀 Workflow

advanced

Joining a Worker Node to a Docker Swarm

Which sequence of commands correctly adds a new worker node to an existing Docker Swarm managed by a manager node?

A 2,1,3,4

B 1,3,2,4

C 1,2,3,4

D 3,2,1,4

💡 Hint

Think about how you get the join token and then use it on the worker.

First, get the join token on the manager, then copy the full join command, run it on the worker, and finally verify the join on the manager.

❓ Troubleshoot

advanced

Error When Worker Node Fails to Join Swarm

A worker node fails to join the swarm and shows the error: Error response from daemon: rpc error: code = Unavailable desc = connection error: connection refused. What is the most likely cause?

A The worker node has an incorrect Docker version

B The worker node cannot reach the manager node on port 2377

C The join token is expired after 24 hours

D The worker node is already part of another swarm

💡 Hint

Consider network connectivity between nodes.

The error indicates the worker cannot connect to the manager's swarm port (2377). Network issues or firewall blocking this port are common causes.

✅ Best Practice

expert

Ensuring High Availability of Manager Nodes

What is the recommended minimum number of manager nodes in a Docker Swarm cluster to ensure high availability and fault tolerance?

A 1

B 2

C 5

D 3

💡 Hint

Think about quorum and consensus in distributed systems.

At least 3 manager nodes are recommended to maintain quorum and allow the swarm to tolerate one manager failure without losing cluster state.