Docker is a containerization platform that packages applications and their dependencies into reusable units called containers. These containers can run on any host with Docker or a similar runtime be it our laptop or a remote cloud server. Docker networking enables us to create a virtual network of these containers, managed by a master node called a manager. This virtual network allows containers to communicate with each other by sharing information, much like connecting devices in a physical or virtual network. When containers are on the same host, they can talk directly without needing to expose ports on the host machine. Docker supports a variety of networks to manage communication between containers, Docker hosts, and the outside world, making it adaptable to a variety of use cases. This article will walk you through some basic commands to get started with Docker networking.
Docker Network Types
In Docker, we use networks to manage how our containers communicate with each other and with external services. For a container to connect to any network, we need to link it to a Docker network. Depending on the network connectivity there are available communication route containers. Docker provides several default network drivers and we can install additional ones using plugins. To see a list of our Docker containers, we can use a specific command.
Bridge : Bridge networks create a virtual bridge between your host and containers, allowing containers to talk to each other while being isolated from the outside network. Each container gets its own IP address, so it can communicate with your local network and the Internet. However, containers will not appear as physical devices on your LAN.
If we create a container without selecting a specific network driver, it will automatically use the bridge network, which is the default.
Host : When we use host network mode for containers, they share the host's network stack without isolation. This means they don't get their own IP address; Instead, any ports they use are exposed directly to the host's network interface. For example, if a container is listening on port 80, it will be accessible via localhost:80. In simple terms, containers will not have separate IP addresses and will be directly integrated into the host's network, eliminating any isolation between Docker hosts and containers.
Overlay : Overlay networks allow containers on different Docker hosts to communicate as if they were on the same network, without the need for special OS-level routing. They are used in Docker Swarm clusters to connect services, but we can also use them for direct communication between containers on individual Docker Engine instances. In simple terms, an overlay network allows multiple Docker engines to connect and different Docker services to talk to each other.
IPvLAN : IPvLAN is a sophisticated network driver that gives detailed control over IPv4 and IPv6 addresses for our containers as well as Layer 2 and 3 VLAN tagging and routing. This driver is particularly useful when integrating containers with an existing physical network. IPvLAN networks have their own interfaces, which can improve performance compared to bridge-based networking. Essentially, with IPvLAN, we have complete control over container addressing and can effectively integrate with physical networks.
MACvLAN : The MacVlan driver is an advanced option that makes containers look like physical devices on your network by assigning each container a unique MAC address. To use Macvlan, we need to dedicate a physical network interface of the host to this virtual network. Additionally, the extensive network should be set up to handle the large number of MAC addresses that may be generated when running many containers. Simply put, the macvlan driver allows us to assign MAC addresses to containers, making them look like separate devices on the network.
Most Preferred network type to use
Bridge networks are generally the best choice in most situations. Hosts on the same network can talk to each other using their own IP addresses and DNS names. They also have access to the host's network, so they can connect to the Internet and our local network.
Host networks are ideal when we want to bind ports directly to our host's network interface and do not need network isolation They allow our containerized apps to act like network services running directly on our host
Overlay networks are essential when you need containers on different Docker hosts to communicate directly. They enable you to create distributed environments, which help set up systems for high availability.
Macvlan networks are useful when containers need to appear as physical devices on our host's network, such as for applications monitoring network traffic. IPvLAN networks are for more advanced setups where we need detailed control over container IP addresses, VLAN tags and routing.
Docker supports third-party network plugins that add additional networking capabilities. For example, Kuryr(it is a Docker network plugin that integrates with OpenStack Neutron to provide networking for containers) integrates OpenStack with Neutron for networking while Wave provides an overlay network that focuses on service discovery, security and fault tolerance.
Finally, Docker networking is optional at the container level. By setting a container's network to "none" we completely disable its networking stack, meaning that the container will not be able to communicate with other containers, access our host's services, or connect to the Internet. This setup increases security by isolating applications that do not need network access
How Docker Networking Works
Docker uses our host's network setup and adjusts iptables rules to route traffic to containers, keeping Docker networks separate from the host system and managing networking.
Iptables is a Linux tool used to filter network traffic. Docker automatically adds rules to iptables to route traffic to our containers, so we don't have to manage these rules ourselves Docker takes care of it.
Docker containers get their own network namespace, creating an isolated virtual network environment. They also set up virtual network interfaces on our host, allowing them to communicate with the outside world through the host's network.
Docker's networking setup is complex and low-level, but Docker makes it easy for users by providing a simple and reliable networking experience for containers. If you want to dive into the technical details, you can check out Docker's documentation. However, more information is available in Docker’s documentation.
Docker Networking vs VM Networking
Docker's networking model creates isolated virtual environments for containers, which handle common networking needs. However, these Docker networks differ from the virtual networks used by traditional VMs in several key ways.
Docker uses namespaces and iptables rules for network isolation, while VMs typically have separate networking stacks for each virtual machine. Additionally, the terminology can be confusing Docker's bridge network is similar to a NAT-based network in many VM solutions.
Generally, VMs can support more different network topologies than what Docker does out of the box. However, Docker provides tools to meet various networking needs, such as using Macvlan to address containers on our physical network or employing third-party plugins to implement additional network models.
KeyPoints of Docker Network
Flexible communication : Docker's networking system allows containers to communicate with each other, their neighbors and the Docker host. Containers within the same network can use names or IP addresses to talk to each other.
Network Drivers : Docker uses different network drivers to meet different needs. These drivers work with the host's network stack but are separated by namespace. This separation is less strict than for VMs, although containers can act as physical devices with Macvlan networks.
Bridge Networking : The default mode, which connects containers to the same host. It is easy to use but does not support direct communication between containers on different hosts.
Overlay network : Allows containers on different hosts to communicate with each other, enabling distributed networks.
DNS : maps container names to IP addresses, ensuring containers are reachable even if IP addresses change. Docker automatically assigns and tracks this name and hostname.
Advantages of Docker Networking
Scalability : Docker allows us to run many containers on a single machine, which can reduce costs. We can use regular hardware instead of buying expensive servers.
Rapid deployment : Docker streamlines the process of packaging and deploying applications, making it faster and less error-prone.
Compatibility : Standardized containers (thanks to the Open Container Initiative) work across different cloud providers and environments, making it easy to move and deploy applications.
Security : Docker isolates applications in separate containers, which helps reduce security risks. It helps manage traffic and applications without impacting the server.
Compatibility : Docker ensures that applications run the same way in development and production, helping to avoid problems when moving from one environment to another.
Disadvanatages of Docker Networking
Outdated documentation : Docker's rapid evolution may outdate its documentation. New features and updates may not have up-to-date guides, making it challenging to find answers when you need them.
Steep learning curve : Docker can be difficult to master, even for those familiar with virtual machines. Learning the basics is manageable, but becoming proficient, especially with advanced features and constant updates, requires significant time and effort.
Security issues : Containers sharing the same operating system can introduce security risks. Unlike virtual machines, which provide strong isolation by running separate operating systems, containers require additional security measures to protect against vulnerabilities.
Limited Orchestration : Docker's built-in orchestration and automation tools are not as advanced as those provided by platforms like Kubernetes. Managing multiple containers and environments often requires additional third-party tools for effective orchestration.
Overall, Docker networking is a feature that helps us to manage how containers communicate, stay secure and remain isolated. It lets us create virtual networks for Docker containers so they can share information and communicate with each other effectively.