Configuring Swarm Networks
1. Creating Overlay Networks
| Option | Values | Description |
|---|---|---|
| docker network create | --driver overlay |
Creates an overlay network using the Docker overlay driver |
| --name | network-name |
Name of the network to be created |
| --subnet | 10.0.0.0/24 |
Subnet for the network (optional) |
| --gateway | 10.0.0.1 |
Gateway IP for the network (optional) |
| --attachable | true |
Allows external non-Swarm containers to connect (optional) |
Example: Creating an Overlay Network
docker network create --driver overlay --subnet=10.0.9.0/24 --gateway=10.0.9.1 my-overlay-network
Note: Overlay networks are only available in swarm mode. The
--driver overlay option is required to create a network that spans multiple Docker daemons.
2. Encrypting Overlay Networks
| Property | Value | Description |
|---|---|---|
| encrypt | true |
Enables encryption for the overlay network |
| key | string |
Encryption key (optional, auto-generated if not provided) |
Example: Create encrypted overlay network
docker network create \
--driver overlay \
--opt encrypted=true \
--opt com.docker.network.driver.mtu=1200 \
my-encrypted-network
Note: Encryption is only available for overlay networks in swarm mode.
Warning: Enabling encryption adds performance overhead. Consider the trade-off between security and performance.
3. Attaching Services to Networks
| Service | Network | Configuration |
|---|---|---|
| web-app | frontend-net |
Attached to frontend-net with --network |
| db-service | backend-net |
Attached to backend-net with --network |
Example: Attaching a Service to a Network
docker service create \
--name web-app \
--network frontend-net \
nginx
Example: Attaching Multiple Services to Same Network
docker service create \
--name api-server \
--network backend-net \
node:18
docker service create \
--name cache-server \
--network backend-net \
redis:latest
Note: Services can be attached to multiple networks using
--network multiple times.
Warning: If a service is not attached to any network, it will be created on the default
ingress network.
4. Publishing Service Ports
| Option | Description | Values | Notes |
|---|---|---|---|
| --publish | Maps a container port to a host port | -p <hostPort>:<containerPort> |
Can be repeated for multiple ports |
| --publish-all | Publishes all exposed ports to random host ports | true |
Use with caution in production |
| --publish-mode | Defines how ports are published | host or ingress |
ingress allows load balancing across nodes |
Example: Publishing with Ingress Mode
docker service create --name api \
--publish published=8081,target=8080,mode=ingress \
node:alpine
5. Configuring Ingress Network
| Property | Description | Default Value | Notes |
|---|---|---|---|
| ingress.network.name | Name of the ingress network | ingress |
Used for routing external traffic to services |
| ingress.network.driver | Driver used for the ingress network | overlay |
Must be overlay for swarm mode |
| ingress.network.subnet | Subnet for the ingress network | 10.255.0.0/16 |
Must not overlap with other networks |
Example: Create Ingress Network with Custom Subnet
docker network create \
--driver overlay \
--subnet 10.255.1.0/24 \
--ingress \
ingress-custom
Note: The
--ingress flag makes the network available for routing external traffic to services.
Warning: Modifying the default ingress network can disrupt service accessibility. Always test in a non-production environment.
6. Setting Up Service Discovery
| Option | Values | Description |
|---|---|---|
| --attachable | true | false |
Allows external containers to connect to the overlay network |
| --driver | overlay |
Network driver for multi-host communication |
| --subnet | 10.0.0.0/24 |
Subnet range for the network |
| --gateway | 10.0.0.1 |
Gateway IP for the network |
Example: Create an Overlay Network
docker network create --driver overlay --subnet=10.0.9.0/24 --gateway=10.0.9.1 swarm-networkExample: Attach Service to Network
docker service create --name webapp --network swarm-network nginx
Note: Service discovery uses DNS-based resolution within the overlay network.
Warning: Ensure all nodes in the swarm are configured to use the same network driver and subnet.
7. Using Network Aliases in Services
Network aliases allow services to be discovered by alternative names within a Docker Swarm network. They provide a way to map a service name to a different DNS name, which can be useful for organizing services or maintaining backward compatibility.
| Property | Description | Example |
|---|---|---|
| --network-alias | Defines an alias for a service within a network | --network-alias web-server |
Example: Defining a Network Alias for a Service
docker service create \
--name web-app \
--network-alias api-server \
--network frontend-network \
nginx
Note: Network aliases are only effective within the scope of a specific network. A service with an alias in one network will not be discoverable under that alias in another network.
8. Configuring Load Balancing
| Option | Values | Description |
|---|---|---|
| --load-balancer | round-robin, least-connections |
Specifies the load balancing algorithm to use for distributing traffic among service tasks. |
| --publish | port |
Exposes a port on the host to make the service accessible externally. |
Example: Load Balancing Configuration
docker service create \
--name my-service \
--publish 80:80 \
--load-balancer round-robin \
nginx
Note: Load balancing is handled automatically by Docker Swarm when using the
docker service create command with exposed ports.
Warning: Ensure that the service tasks are running on different nodes to effectively distribute load.
9. Managing Routing Mesh
| Property | Description | Default Value | Notes |
|---|---|---|---|
| routing.mesh | Enables or disables the routing mesh for service discovery | true |
Routing mesh allows services to communicate across nodes in a swarm |
| routing.mesh.subnet | Subnet used for the routing mesh overlay network | 10.255.0.0/16 |
Must not overlap with existing networks |
Example: Configure Routing Mesh Subnet
docker network create \
--driver overlay \
--subnet=10.255.1.0/24 \
--opt com.docker.network.overlay.rx_bandwidth=100mb \
--opt com.docker.network.overlay.tx_bandwidth=100mb \
routing-mesh-net
Note: The routing mesh is automatically managed by Docker Swarm, but can be customized for specific network configurations.
10. Configuring External Load Balancers
| Configuration | Description | Example |
|---|---|---|
| --external-load-balancer | Flag to enable external load balancing in swarm mode | docker service create --external-load-balancer <lb-name> <image> |
| --publish | Expose ports to the host network | docker service create --publish 80:80 <image> |
| --network | Attach service to a specific network | docker service create --network my-network <image> |
Example: External Load Balancer Setup
docker service create \
--name my-app \
--publish 80:80 \
--external-load-balancer lb-123 \
nginx
Note: External load balancers must be configured outside of Docker Swarm, typically via cloud providers or dedicated hardware.
11. Using Attachable Overlay Networks
Attachable overlay networks in Docker Swarm allow containers to connect to a network manually, rather than being automatically attached when starting a service. This is useful for debugging or connecting standalone containers to Swarm services.
| Property | Value | Description |
|---|---|---|
| driver | overlay |
The network driver to use for the overlay network |
| attachable | true |
Enables manual attachment of containers to the network |
| name | my-attachable-network |
Name of the network to be created |
Example: Creating an Attachable Overlay Network
docker network create --driver overlay --attachable my-attachable-networkExample: Attaching a Container to the Network
docker run --network my-attachable-network alpine ping -c 3 google.com
Note: The
attachable property must be set to true when creating the network for it to be manually attached.
Warning: Attachable networks are not suitable for production services due to potential security and performance implications.
12. Troubleshooting Swarm Networking
Common Issues and Solutions
- Containers cannot communicate across services: Check if the services are using the same network and that the network is attached to the correct scope (swarm or local).
- Port mapping issues: Ensure that the published ports are correctly mapped and that there is no port conflict on the host.
- Service discovery fails: Verify that DNS resolution is enabled in the network configuration and that services are using the correct service names.
- Network performance degradation: Check for network bottlenecks or misconfigurations in the overlay network.
| Issue | Possible Cause | Solution |
|---|---|---|
| Service not reachable | Incorrect network configuration or service name typo | Verify the network and service names in docker service inspect |
| Port conflicts | Host port already in use or misconfigured | Use docker service update --publish-add to change port mapping |
| Overlay network not functioning | Network misconfiguration or Docker daemon issues | Recreate the overlay network with docker network rm and docker network create |
Note: Use
docker network ls to list all networks and verify that the swarm network is active.
Warning: When troubleshooting, avoid modifying network configurations while services are running to prevent service disruption.