Overlay networks in Swarm in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to create an overlay network named 'mynetwork' in Docker Swarm.

Docker

docker network create -d [1] mynetwork

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

Abridge

Boverlay

Chost

Dmacvlan

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' driver which only works on a single host.

Using 'host' which shares the host network stack.

Using 'macvlan' which is for direct host network access.

The overlay driver is used to create networks that span multiple Docker hosts in a Swarm cluster.

2fill in blank

medium

Complete the command to attach a service named 'web' to the overlay network 'mynetwork'.

Docker

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

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

Ahost

Bbridge

Cdefault

Dmynetwork

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' which is not the overlay network.

Using 'host' which bypasses Docker networking.

Using 'default' which may not exist or be overlay.

The service must be attached to the overlay network mynetwork to communicate across Swarm nodes.

3fill in blank

hard

Fix the error in the command to inspect the overlay network named 'mynetwork'.

Docker

docker network [1] mynetwork

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

Ainspect

Bcreate

Crm

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'list' which shows all networks but not details.

Using 'create' which tries to make a new network.

Using 'rm' which deletes the network.

The inspect command shows detailed information about a specific network.

4fill in blank

hard

Fill both blanks to create an overlay network with encryption enabled and attach it to a service named 'db'.

Docker

docker network create -d [1] --opt encrypted=[2] secure_net && docker service create --name db --network secure_net postgres

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

Aoverlay

Btrue

Cfalse

Dbridge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' driver which does not support encryption in Swarm.

Setting encrypted option to 'false' which disables encryption.

Overlay networks support encryption with the --opt encrypted=true option. The driver must be 'overlay'.

5fill in blank

hard

Fill all three blanks to create a service named 'app' attached to two overlay networks 'frontend' and 'backend'.

Docker

docker network create -d [1] frontend && docker network create -d [2] backend && docker service create --name app --network [3] nginx

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

Aoverlay

Bbridge

Cfrontend

Dbackend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' driver which is not for Swarm overlay networks.

Confusing network names in the service command.

Both networks must use the 'overlay' driver. The service is attached to the 'frontend' network first.

Practice

1. What is the main purpose of an overlay network in Docker Swarm?

easy

A. To provide a graphical interface for managing containers

B. To isolate containers within the same host only

C. To store container logs centrally

D. To enable communication between containers on different Docker hosts

Solution

1. Step 1: Understand overlay network function

   An overlay network connects containers running on different Docker hosts, allowing them to communicate as if on the same network.

2. Step 2: Compare options

   Options A, B, and D describe other features unrelated to overlay networks. Only To enable communication between containers on different Docker hosts correctly describes the main purpose.

3. Final Answer:

   To enable communication between containers on different Docker hosts -> Option D

4. Quick Check:

   Overlay network = cross-host container communication [OK]

Hint: Overlay networks connect containers across hosts, not just one host [OK]

Common Mistakes:

• Thinking overlay networks only work on one host
• Confusing overlay networks with logging or UI features
• Assuming overlay networks isolate containers instead of connecting them

2. Which command correctly creates an overlay network named mynetwork in Docker Swarm?

easy

A. docker network create --driver overlay mynetwork

B. docker network create --driver bridge mynetwork

C. docker swarm network create mynetwork

D. docker create network overlay mynetwork

Solution

1. Step 1: Identify correct command syntax

   The correct syntax to create an overlay network is docker network create --driver overlay [name].

2. Step 2: Evaluate options

   docker network create --driver bridge mynetwork uses the bridge driver, not overlay. docker swarm network create mynetwork is invalid syntax. docker create network overlay mynetwork is incorrect command order. Only docker network create --driver overlay mynetwork is correct.

3. Final Answer:

   docker network create --driver overlay mynetwork -> Option A

4. Quick Check:

   Correct overlay network creation uses --driver overlay [OK]

Hint: Use 'docker network create --driver overlay' to create overlay networks [OK]

Common Mistakes:

• Using bridge driver instead of overlay
• Incorrect command order or missing 'network' keyword
• Confusing swarm commands with network commands

3. Given the following Docker Swarm overlay network creation command:

docker network create -d overlay --attachable mynet

What does the --attachable flag do?

medium

A. Limits the network to only swarm services

B. Prevents services from using the network

C. Allows standalone containers to connect to the overlay network

D. Automatically attaches volumes to containers

Solution

1. Step 1: Understand the --attachable flag

   The --attachable flag allows standalone containers (not part of swarm services) to connect to the overlay network.

2. Step 2: Analyze options

   Prevents services from using the network is false because it does not prevent services. Limits the network to only swarm services is opposite of what attachable does. Automatically attaches volumes to containers is unrelated to networks.

3. Final Answer:

   Allows standalone containers to connect to the overlay network -> Option C

4. Quick Check:

   --attachable = standalone container access [OK]

Hint: Attachable lets normal containers join overlay networks [OK]

Common Mistakes:

• Thinking --attachable restricts network to swarm services
• Confusing attachable with volume or storage options
• Assuming it disables service connections

4. You created an overlay network with:

docker network create -d overlay mynet

But when you try to connect a standalone container using docker run --net mynet, it fails. What is the likely cause?

medium

A. The overlay network was not created with the --attachable flag

B. The container image is incompatible with overlay networks

C. Docker Swarm mode is not initialized

D. The container must be part of a service to use overlay networks

Solution

1. Step 1: Identify overlay network usage for standalone containers

   Standalone containers can only connect to overlay networks if the network was created with --attachable.

2. Step 2: Evaluate other options

   The container image is incompatible with overlay networks is incorrect; container images do not affect network connection. Docker Swarm mode is not initialized is unrelated if network was created. The container must be part of a service to use overlay networks is false because attachable networks allow standalone containers.

3. Final Answer:

   The overlay network was not created with the --attachable flag -> Option A

4. Quick Check:

   Standalone container needs --attachable network [OK]

Hint: Add --attachable to overlay network for standalone containers [OK]

Common Mistakes:

• Ignoring the need for --attachable flag
• Blaming container image compatibility
• Assuming all overlay networks allow standalone containers

5. You want to deploy a multi-host Docker Swarm service that uses an overlay network named swarmnet. You also want to allow some standalone containers to join this network for debugging. Which sequence of commands correctly sets this up?

hard

A. docker network create -d overlay swarmnetdocker service create --network swarmnet myservice

B. docker network create -d overlay --attachable swarmnetdocker service create --network swarmnet myservice

C. docker network create -d bridge --attachable swarmnetdocker service create --network swarmnet myservice

D. docker network create --driver overlay swarmnetdocker run --net swarmnet myservice

Solution

1. Step 1: Create overlay network with attachable flag

   To allow standalone containers to join, the overlay network must be created with --attachable.

2. Step 2: Deploy service on the created network

   Use docker service create --network swarmnet myservice to deploy the service on the overlay network.

3. Step 3: Analyze options

   docker network create -d overlay swarmnet
   docker service create --network swarmnet myservice misses --attachable, so standalone containers cannot join. docker network create -d bridge --attachable swarmnet
   docker service create --network swarmnet myservice uses bridge driver, which is not multi-host. docker network create --driver overlay swarmnet
   docker run --net swarmnet myservice tries to run a service as a container, which is incorrect.

4. Final Answer:

   docker network create -d overlay --attachable swarmnet and docker service create --network swarmnet myservice -> Option B

5. Quick Check:

   Attachable overlay network + service create = correct setup [OK]

Hint: Use --attachable overlay network for standalone container access [OK]

Common Mistakes:

• Omitting --attachable flag for standalone containers
• Using bridge driver for multi-host networking
• Confusing service create with container run commands