Docker Network

Docker: Network

1. Infrastructure as Code: Networking

Networking for container
  • How can services provided by a container become available to the world?
    • Piggyback on the host machine’s network.
  • Docker has supporting drivers for containers:
    • bridge: The default network driver.
    • host: Remove network isolation between the container and the Docker host.
    • none: Completely isolate a container from the host and other containers.
    • overlay: Overlay networks connect multiple Docker daemons together.
    • ipvlan: IPvlan networks provide full control over both IPv4 and IPv6 addressing.
    • macvlan: Assign a MAC address to a container.
Docker network commands
  • docker network will list all possible command options
docker network
  • docker network ls will list all possible networks
docker network ls
  • Default network: bridge
  • compute, csc418env_default, docker-spark_default, and docker_default: Dr. Ngo’s custom networks
  • docker network inspect NAME: inspect the NAME network
docker network inspect bridge
  • By default, new containers are attached to the bridge network
Attaching a new container
  • Run the following command to launch a nodejs container


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docker run -itd node:slim
  • Inspect the bridge network to learn about the container.

2. Port mapping

Overview
  • Why do we have to map ports?
    • By default, containers are not exposed to the world.
    • Internally to host, containers have their own private addresses
      • Services have to be exposed port by port.
      • These have to be mapped to avoid conflicts.
Hands on: A simple web server
A baseline node.js server
  • If you don’t already have one running from the previous section, run the following command to launch a nodejs container


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docker run -itd --name my_nodejs node:slim
  • Check the status of the running container


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docker ps
  • Open a terminal into the running container using docker exec 


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docker exec -it my_nodejs sh
  • Inside the my_nodejs container, install nano and curl:


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apt update
apt install -y nano curl
  • Create a directory called app under the root directory. Use nano to create a file called server.js with the following contents

```js linenums=”1” const { createServer } = require(‘node:http’); const hostname = ‘0.0.0.0’; const port = 3000; const server = createServer((req, res) => { res.statusCode = 200; res.setHeader(‘Content-Type’, ‘text/plain’); res.end(‘Hello World’); }); server.listen(port, hostname, () => { console.log(Server running at http://${hostname}:${port}/); });



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- Launch the server using the following commands

```bash
cd /app
node server.js
CLI access
  • Open another terminal and use docker exec to get into the running my_nodejs container.
  • Run curl 127.0.0.1:3000. What is the outcome?
Host machine browser access
  • Open a browser on the host machine
  • Visit 127.0.0.1:3000. What is the outcome?
Commit the image
  • Stop the my_nodejs container.
  • Commit the container into an image called my_nodejs:1.0. This is for the next step of the hands-on
A node.js server with port mapping
  • Launch a container from the newly created my_nodejs:1.0 image


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docker run -itd -P --expose 3000 --name my_nodejs my_nodejs:1.0 sh
cd /app
node server.js
Host machine browser access
  • Find the mapped port using docker ps or the Docker Desktop dashboard
  • Open a browser on the host machine and visit 127.0.0.1 at the shown mapped port (most likely 5 digits)
  • What is the outcome?
  • -P: make this service reachable from other computers (--publish-all)
  • --expose : Open a port from inside the container
Where are the ports?
Hands on: manual allocation of port numbers
  • In the previous example, the port randomly assigned by the host machine was random.
  • This could be specified via the -p flag as follows:


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docker run -itd -p 30080:3000 --expose 3000 --name my_nodejs my_nodejs:1.0 sh
  • Convention: port-on-host:port-on-container
  • Delete the previous container and rerun it with the new -p flag.
  • Revisit the host machine browser at 127.0.0.1:30080 to confirm that the Node server inside the container is still reachable.

3. Port mapping on a Cloud Node

Branching your Cloud profile
  • On your Github repository for CloudLab, create a branch called docker from the main branch.
  • Make sure that your docker branch contains all files from Dr. Ngo’s cloudlab repository’s docker branch.
  • Go to your CloudLab, and open up the corresponding CloudLab profile.
  • Edit and Update the link to the GitHub repository.
  • You should see a branch called docker added to the Repository Branches and Tags of your CloudLab profile.
  • Click on the Instantiate button for this branch.
Hands-on exercise
  • Repeat all the activities from Section 2, Port mapping.
  • For the browser test, use the host name of your experiment with the corresponding mapped port instead of localhost or 127.0.0.1.

4. Common Networking Tasks in Docker

Create a network 


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docker network create --driver bridge ramnet
docker network ls
Place a container on a network 


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docker run -d --name es --net ramnet elasticsearch:2
docker network inspect ramnet
Place another container on a network 


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docker run -it --net ramnet alpine sh
ping es
  • Open another terminal and inspect ramnet