How to create an overlay network in Docker Swarm

Introduction

Docker Swarm is a powerful tool for orchestrating and managing containerized applications at scale. One of the key features of Docker Swarm is the ability to create overlay networks, which allow containers to communicate securely and efficiently across multiple hosts. In this tutorial, we will guide you through the process of creating an overlay network in Docker Swarm and deploying services on it.

Skills Graph

Introduction to Docker Overlay Networks

Docker Overlay Networks are a powerful feature in Docker Swarm, enabling seamless communication between containers deployed across multiple Docker hosts. These networks provide a virtual network layer that abstracts the underlying physical network infrastructure, allowing containers to connect and communicate as if they were running on the same host.

Understanding Docker Overlay Networks

Docker Overlay Networks are based on the VXLAN (Virtual Extensible LAN) protocol, which allows for the creation of a Layer 2 virtual network over a Layer 3 network. This enables containers to be connected to the same logical network, regardless of their physical location.

The key benefits of using Docker Overlay Networks include:

1. Multi-host Connectivity: Containers can communicate with each other across multiple Docker hosts, enabling scalable and distributed application deployments.
2. Automatic Service Discovery: Containers on the same overlay network can discover and connect to each other using the built-in DNS service provided by Docker Swarm.
3. Load Balancing: Docker Swarm's load balancing capabilities can be leveraged to distribute traffic across multiple replicas of a service running on the overlay network.
4. Secure Communication: Docker Overlay Networks support encryption, ensuring secure communication between containers on different hosts.

Overlay Network Architecture

Docker Overlay Networks are built on top of the Docker Swarm clustering and orchestration system. Each Swarm node (manager or worker) participates in the overlay network, contributing to the overall network topology and routing.

The key components of the Docker Overlay Network architecture are:

1. VXLAN Tunnel Endpoint (VTEP): Each Swarm node runs a VTEP, which is responsible for encapsulating and decapsulating network traffic between containers on the overlay network.
2. Overlay Network Database: A distributed database, such as Raft, is used to store the overlay network configuration and routing information, ensuring consistency and availability across the Swarm cluster.
3. Overlay Network Driver: The Docker Overlay Network driver is responsible for managing the creation, configuration, and maintenance of the overlay network.

By understanding the underlying concepts and architecture of Docker Overlay Networks, you'll be better equipped to create and manage these networks in your Docker Swarm environment.

Creating an Overlay Network in Docker Swarm

Creating an overlay network in Docker Swarm is a straightforward process. In this section, we'll walk through the steps to create an overlay network and configure it for use in your Docker Swarm environment.

Prerequisites

Before creating an overlay network, ensure that you have the following:

1. A Docker Swarm cluster with at least one manager node and one worker node.
2. The Docker Engine version should be 17.06 or later, as earlier versions may not support the full range of overlay network features.

Creating the Overlay Network

To create an overlay network in Docker Swarm, follow these steps:

1. Connect to a Docker Swarm manager node.
2. Run the following command to create an overlay network:

docker network create --driver overlay --attachable my-overlay-network

In this example, we're creating an overlay network named my-overlay-network with the --attachable flag, which allows standalone containers to connect to the network.

Verifying the Overlay Network

After creating the overlay network, you can verify its creation and inspect its details using the following commands:

## List all networks in the Docker Swarm
docker network ls

## Inspect the details of the overlay network
docker network inspect my-overlay-network

The output of the docker network inspect command will provide information about the overlay network, including the subnet, gateway, and the list of nodes participating in the network.

Deploying Services on the Overlay Network

Once the overlay network is created, you can deploy services on it. When creating a service, you can specify the network it should be attached to using the --network flag:

docker service create --name my-service --network my-overlay-network nginx:latest

This will create a new service named my-service and attach it to the my-overlay-network overlay network.

By following these steps, you can create and manage overlay networks in your Docker Swarm environment, enabling secure and scalable communication between containers across multiple hosts.

Deploying Services on the Overlay Network

Now that you have created an overlay network in your Docker Swarm, you can start deploying services on it. In this section, we'll explore how to deploy services on the overlay network and take advantage of its features.

Attaching Services to the Overlay Network

When creating a new service in Docker Swarm, you can specify the network it should be attached to using the --network flag. This ensures that the service's containers are connected to the overlay network and can communicate with other services on the same network.

docker service create --name my-service --network my-overlay-network nginx:latest

In this example, we're creating a new service named my-service and attaching it to the my-overlay-network overlay network.

Service Discovery and Load Balancing

One of the key benefits of using an overlay network is the built-in service discovery and load balancing capabilities provided by Docker Swarm. When services are deployed on the overlay network, they can discover and communicate with each other using the Swarm's internal DNS service.

Docker Swarm's load balancing mechanism automatically distributes traffic across the replicas of a service, ensuring high availability and scalability.

Secure Communication

Docker Overlay Networks support encryption, ensuring secure communication between containers on different hosts. This is particularly important when deploying sensitive applications or services that require end-to-end encryption.

Scaling Services

As your application grows, you can easily scale your services by adding more replicas. Docker Swarm will automatically handle the network configuration and load balancing for the new replicas, ensuring that they can seamlessly communicate with other services on the overlay network.

docker service scale my-service=5

This command will scale the my-service to 5 replicas, and Docker Swarm will ensure that the new replicas are connected to the overlay network and can be reached by other services.

By deploying services on the Docker Overlay Network, you can take advantage of the seamless connectivity, service discovery, load balancing, and security features provided by Docker Swarm, making it easier to build and manage scalable, distributed applications.

Summary

In this comprehensive tutorial, you have learned how to create an overlay network in Docker Swarm, a crucial step in building scalable and interconnected Docker-based applications. By leveraging the power of overlay networks, you can enable seamless communication between your containerized services, ensuring a robust and efficient infrastructure. With the knowledge gained from this guide, you can now confidently manage and optimize your Docker Swarm environment for your specific needs.