Swarm mode initialization in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to initialize Docker Swarm mode on the current machine.

Docker

docker swarm [1]

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

Alaunch

Bstart

Ccreate

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' instead of 'init' which is not a valid swarm command.

Using 'create' or 'launch' which are not Docker swarm commands.

The docker swarm init command initializes the current machine as a Swarm manager.

2fill in blank

medium

Complete the command to specify the advertise address when initializing Docker Swarm.

Docker

docker swarm init --advertise-addr [1]

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

Alocalhost

B192.168.1.100

C0.0.0.0

D255.255.255.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'localhost' which is not reachable by other nodes.

Using '0.0.0.0' which is a wildcard and invalid here.

Using a subnet mask like '255.255.255.0' instead of an IP address.

The --advertise-addr option requires the IP address that other nodes will use to connect to this manager.

3fill in blank

hard

Fix the error in the command to initialize Docker Swarm with a specific listen address.

Docker

docker swarm init --listen-addr [1]

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

A192.168.1.100:2377

Blocalhost:2377

C192.168.1.100

D0.0.0.0

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the port number after the IP address.

Using 'localhost' which is not reachable by other nodes.

Using '0.0.0.0' which is invalid here.

The --listen-addr option requires an IP address and port, usually port 2377 for Swarm communication.

4fill in blank

hard

Fill both blanks to create a command that initializes Docker Swarm with a specific advertise and listen address.

Docker

docker swarm init --advertise-addr [1] --listen-addr [2]

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

A192.168.1.101

B192.168.1.102:2377

C192.168.1.101:2377

Dlocalhost

Attempts:

3 left

💡 Hint

Common Mistakes

Using IP with port for advertise address.

Using IP without port for listen address.

Using 'localhost' which is not valid for these options.

The advertise address is just the IP, while the listen address includes IP and port.

5fill in blank

hard

Fill all three blanks to create a command that initializes Docker Swarm with a specific advertise address, listen address, and a custom data path.

Docker

docker swarm init --advertise-addr [1] --listen-addr [2] --data-path-port [3]

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

A192.168.1.110

B192.168.1.110:2377

C4789

D2377

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing listen port with data path port.

Using IP with port for advertise address.

Using invalid port numbers.

The --data-path-port option sets the port for overlay network data traffic, default is 4789.

Practice

1. What is the main purpose of running docker swarm init?

easy

A. To add a new worker node to an existing swarm

B. To create a new Docker swarm cluster and make the current node a manager

C. To remove a node from a swarm

D. To update Docker to the latest version

Solution

1. Step 1: Understand the command purpose

   docker swarm init is used to start a new swarm cluster and make the current node the manager.

2. Step 2: Differentiate from other swarm commands

   Adding nodes uses docker swarm join, not init. Removing nodes or updating Docker are unrelated.

3. Final Answer:

   To create a new Docker swarm cluster and make the current node a manager -> Option B

4. Quick Check:

   Swarm init = create manager node [OK]

Hint: Init creates manager; join adds workers [OK]

Common Mistakes:

• Confusing init with join command
• Thinking init updates Docker
• Assuming init removes nodes

2. Which of the following is the correct syntax to initialize a swarm with a specific advertise address?

easy

A. docker swarm create --advertise 192.168.1.10

B. docker swarm start --advertise-addr 192.168.1.10

C. docker swarm init --advertise-addr 192.168.1.10

D. docker swarm init -a 192.168.1.10

Solution

1. Step 1: Recall correct command syntax

   The correct command to initialize swarm with advertise address is docker swarm init --advertise-addr <IP>.

2. Step 2: Identify incorrect options

   docker swarm start and docker swarm create are invalid commands. The short flag -a is not recognized for advertise address.

3. Final Answer:

   docker swarm init --advertise-addr 192.168.1.10 -> Option C

4. Quick Check:

   Use --advertise-addr with init [OK]

Hint: Use full flag --advertise-addr with init [OK]

Common Mistakes:

• Using 'start' or 'create' instead of 'init'
• Using short flag '-a' which is invalid
• Omitting --advertise-addr flag

3. What will be the output of the command docker swarm init --advertise-addr 10.0.0.5 if the node is already part of a swarm?

medium

A. Error: This node is already part of a swarm

B. Swarm initialized successfully with advertise address 10.0.0.5

C. Warning: Advertise address ignored, node already in swarm

D. Swarm initialized but advertise address not set

Solution

1. Step 1: Understand swarm init behavior on existing swarm node

   If a node is already in a swarm, running docker swarm init again causes an error because it cannot reinitialize.

2. Step 2: Check output messages

   The command will output an error message indicating the node is already part of a swarm, not success or warning.

3. Final Answer:

   Error: This node is already part of a swarm -> Option A

4. Quick Check:

   Init on existing swarm node = error [OK]

Hint: Init fails if node already in swarm [OK]

Common Mistakes:

• Assuming init overwrites existing swarm
• Expecting a warning instead of error
• Thinking advertise address is ignored silently

4. You ran docker swarm init --advertise-addr 192.168.0.100 but other nodes cannot join the swarm. What is the most likely problem?

medium

A. The join token expired immediately after init

B. You forgot to run docker swarm join on the manager node

C. Swarm mode is not supported on this Docker version

D. The advertise address is set to an IP not reachable by other nodes

Solution

1. Step 1: Analyze advertise address role

   The advertise address tells other nodes where to connect. If it is set to an IP unreachable by others, they cannot join.

2. Step 2: Evaluate other options

   Join tokens are used on worker nodes, not manager. Swarm mode is supported in modern Docker versions. Join tokens do not expire immediately.

3. Final Answer:

   The advertise address is set to an IP not reachable by other nodes -> Option D

4. Quick Check:

   Advertise address must be reachable [OK]

Hint: Check advertise IP reachability for joining nodes [OK]

Common Mistakes:

• Trying to join on manager node
• Assuming join tokens expire instantly
• Ignoring network connectivity issues

5. You want to initialize a swarm on a node with multiple network interfaces. Which command ensures other nodes connect via the interface with IP 172.16.5.10?

hard

A. docker swarm init --advertise-addr 172.16.5.10

B. docker swarm init --listen-addr 172.16.5.10

C. docker swarm init --advertise-addr eth1

D. docker swarm init --interface 172.16.5.10

Solution

1. Step 1: Identify correct flag for advertise address

   The --advertise-addr flag sets the IP address other nodes use to connect to the manager.

2. Step 2: Eliminate incorrect options

   --listen-addr sets the address the manager listens on internally, not what others connect to. Using interface name or unknown flags is invalid.

3. Final Answer:

   docker swarm init --advertise-addr 172.16.5.10 -> Option A

4. Quick Check:

   Use --advertise-addr with IP for multi-interface nodes [OK]

Hint: Use IP with --advertise-addr, not interface name [OK]

Common Mistakes:

• Using --listen-addr instead of --advertise-addr
• Passing interface name instead of IP
• Using unsupported flags like --interface