Scenario: A developer needs to connect and manage container networks using Moby’s networking features. In this example, we will create and manage an overlay network to enable inter-container communications.
Background: Moby Project is an open-source project that advances the software containerization movement. It provides a library of components, a framework for assembling them into custom container-based systems, and a place for container enthusiasts to experiment and exchange ideas. Docker is a popular open-source container platform that uses the Moby Project as an open R&D lab for experimenting and developing new components.
Networking in Containers: Containers have no information about the type of network they are attached to or whether their peers are Docker workloads or not. They only see a network interface with an IP address, a gateway, a routing table, DNS services, and other networking details.
Overlay Networks: Overlay networks abstract the underlying network topology and provide a logical network layer on top of the physical network. They are useful when inter-container communications may break when 1000 containers are co-located on the same host.
Prerequisites:
- Familiarity with Docker and containerization concepts
- Docker installed and running on your system
Step 1: Create a new Docker network using the overlay driver:
$ docker network create --driver=overlay my-overlay-network
Step 2: Run two containers using the created network:
# Container 1
$ docker run --name container1 --network my-overlay-network -it alpine sh
# Container 2
$ docker run --name container2 --network my-overlay-network -it alpine sh
Step 3: Verify the containers can communicate with each other:
# Container 1 ping container2
$ ping container2
PING container2 (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: icmp_seq=0 ttl=64 time=0.115 ms
64 bytes from 172.17.0.2: icmp_seq=1 ttl=64 time=0.115 ms
# Container 2 ping container1
$ ping container1
PING container1 (172.17.0.1): 56 data bytes
64 bytes from 172.17.0.1: icmp_seq=0 ttl=64 time=0.115 ms
64 bytes from 172.17.0.1: icmp_seq=1 ttl=64 time=0.115 ms
Step 4: Test the network with multiple containers:
# Run more containers and test their connectivity
$ docker run --name container3 --network my-overlay-network -it alpine sh
$ docker run --name container4 --network my-overlay-network -it alpine sh
# Test connectivity between containers
$ docker exec container1 ping container3
$ docker exec container3 ping container1
$ docker exec container1 ping container4
$ docker exec container4 ping container1
Tests:
- Create an overlay network with at least 3 containers and verify their connectivity.
- Add more containers to the network and test their connectivity.
- Remove a container from the network and test the connectivity of the remaining containers.
Conclusion: In this example, we demonstrated how to create and manage an overlay network using Moby’s networking features. Overlay networks provide a logical network layer on top of the physical network, enabling inter-container communications and abstracting the underlying network topology. This example can be extended to include more complex scenarios, such as multiple subnets, security groups, and load balancing.
