Docker Networking
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Docker networking allows containers to communicate in several ways. Containers can communicate using Docker's default bridge (Docker0), by binding container ports to the host's ports, or using the host's network stack directly. More advanced options include linking containers to share information, using overlay networks with technologies like Open vSwitch, or running containers across multiple hosts with tunnels. The document provides examples of setting up different Docker networking configurations and discusses which methods suit different communication requirements between containers, hosts, and external networks.
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Docker Networking
- 1. Docker Networking Kingston Smiler. S (kingstonsmiler@gmail.com)
- 2. Agenda Introduction and Key Concepts Docker Communication requirement Different methods of Docker networking Sample Setup Limitation of current Docker Networking
- 3. Docker Networking - Introduction Concept Description Network Namespace Provide a way of having separate network stack for each instance of a container. Docker0 Bridge Default bridge created by docker to provide communication across docker containers and external world including the host. Port Mapping Mechanism to map a port in the host machine with the Docker container’s networking stack. Veth Pair Veth is a special, logical, virtual interface which is similar to a link / pipe. It has two ends which are logical interfaces and provide connectivity across two different network elements.
- 4. Different Communication Requirement Container – Container Communication Container to Host Communication Container to External world communication. Container - Container communication across containers running in different host. Cont 1 Cont 2 Cont 3 Docker0/OVS Port Map Host1 etho
- 5. Different Methods of Docker Networking Docker Bridging Host Port Binding to Docker Docker network using host network stack (--net=host) Docker communication using –net=container Docker Container linking using –link option Docker Networking Using OVS (Advanced)
- 6. Docker Bridging Docker0 bridge Virtual bridge similar to linux bridge Created in the host machine during the creation of Docker container. Veth Pair Will be created during the creation of Docker container. One end of the veth pair is attached to the eth0 interface of Docker container Another end is attached to the docker0 bridge with interface name starts with vethc3cd.
- 7. Host Port Binding To Docker Container In this method, a port in the host machine will be bound to a port in Docker. Simple way of running a service in Docker container and exposing the service to external world. Example case is, running a webserver in the docker container and forwarding all the web traffic which is coming to the HTTP port in host machine to Docker container. -p IP:host_port:container_port option does it. /usr/bin/docker run -d --name port_forward -p 80:80 ubuntu_apache /usr/sbin/apache2ctl -D FOREGROUND This operation is similar to NAT. Two or more container won’t be able to provide the same service on same host port.
- 8. Docker Network Using Host Network Stack Docker container can use the host machines networking stack instead of having a separate network stack. One way of making containers talk to external world. --net=host option does it /usr/bin/docker run -d --name h1 --net=host ubuntu_ftp vsftpd If two containers in the host system prefers to use this mechanism then, port collision across the container happens.
- 9. Docker Communication Using Other Docker’s Network Stack Simple way of making containers talk to each other. Uses other Docker’s networking stack instead of having a separate network stack. Similar to –net=host option. But here instead of using the host machines network stack, it uses some other Docker’s network stack. The two containers can talk to each other by using loopback interface. --net=host option does it /usr/bin/docker run -d --name cont_net1 --net=container:b1 ubuntu /bin/sh -c "while true; do echo Hello World; sleep 1; done"
- 10. Docker Communication Using Link Provides a mechanism for Docker container to transfer information from one container to another securely. No ports are explicitly exposed to the destination container by source. Unidirectional Conduit / Pipe between source and destination container. Information about the service which is running in the source container will be exposed to the destination. Simple way of providing service chaining in docker environment. making containers talk to each other. docker run -d -P --name link_dest --link port_forward:link1 ubuntu /bin/sh -c "while true; do echo Hello World; sleep 1; done"
- 11. Requirement Vs Communication Methods Container – Container Communication Docker0 bridge (Cont1 – Cont2 via Docker0) Container networking using –net=container option (Cont4 – Cont5) UDS / pipe (Cont1 – Cont2) Container linking using –link option OVS (Cont1 – Cont2 via OVS) Container to Host Communication Host networking using –net=host option (Cont6) Docker0 bridge (Cont1, Cont2, Cont4) Container to External world communication. Port Mapping (Cont 3) Host networking using –net=host option (Cont 6) Container - Container communication across containers running in different host. OVS Cont 4 Cont 5 Cont 6 Docker0/OVS Host Network Host 2 Cont 1 Cont 2 Cont 3 Docker0/OVS Port Map Host1 Veth Pair UDS / Pipe GRE / VXLAN Tunnel Port Map --net=host option --net = container option Eth 1 Eth 1
- 12. Sample Setup b1 Host Network Stack Host VM Machine b2 Link dest h1 Port forward Cont net1 enp0s3 enp0s8 Docker0/OVS