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234 lines
5.2 KiB
Markdown
234 lines
5.2 KiB
Markdown
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class: title
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# Container networking basics
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---
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## Objectives
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We will now run network services (accepting requests) in containers.
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At the end of this section, you will be able to:
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* Run a network service in a container.
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* Manipulate container networking basics.
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* Find a container's IP address.
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We will also explain the different network models used by Docker.
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---
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## A simple, static web server
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Run the Docker Hub image `nginx`, which contains a basic web server:
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```bash
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$ docker run -d -P nginx
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66b1ce719198711292c8f34f84a7b68c3876cf9f67015e752b94e189d35a204e
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```
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* Docker will download the image from the Docker Hub.
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* `-d` tells Docker to run the image in the background.
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* `-P` tells Docker to make this service reachable from other computers.
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<br/>(`-P` is the short version of `--publish-all`.)
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But, how do we connect to our web server now?
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---
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## Finding our web server port
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We will use `docker ps`:
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```bash
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$ docker ps
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CONTAINER ID IMAGE ... PORTS ...
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e40ffb406c9e nginx ... 0.0.0.0:32768->80/tcp ...
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```
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* The web server is running on port 80 inside the container.
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* This port is mapped to port 32768 on our Docker host.
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We will explain the whys and hows of this port mapping.
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But first, let's make sure that everything works properly.
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---
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## Connecting to our web server (GUI)
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Point your browser to the IP address of your Docker host, on the port
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shown by `docker ps` for container port 80.
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---
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## Connecting to our web server (CLI)
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You can also use `curl` directly from the Docker host.
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Make sure to use the right port number if it is different
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from the example below:
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```bash
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$ curl localhost:32768
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<!DOCTYPE html>
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<html>
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<head>
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<title>Welcome to nginx!</title>
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...
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```
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---
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## How does Docker know which port to map?
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* There is metadata in the image telling "this image has something on port 80".
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* We can see that metadata with `docker inspect`:
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```bash
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$ docker inspect --format '{{.Config.ExposedPorts}}' nginx
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map[80/tcp:{}]
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```
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* This metadata was set in the Dockerfile, with the `EXPOSE` keyword.
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* We can see that with `docker history`:
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```bash
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$ docker history nginx
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IMAGE CREATED CREATED BY
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7f70b30f2cc6 11 days ago /bin/sh -c #(nop) CMD ["nginx" "-g" "…
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<missing> 11 days ago /bin/sh -c #(nop) STOPSIGNAL [SIGTERM]
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<missing> 11 days ago /bin/sh -c #(nop) EXPOSE 80/tcp
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```
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---
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## Why are we mapping ports?
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* We are out of IPv4 addresses.
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* Containers cannot have public IPv4 addresses.
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* They have private addresses.
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* Services have to be exposed port by port.
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* Ports have to be mapped to avoid conflicts.
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---
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## Finding the web server port in a script
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Parsing the output of `docker ps` would be painful.
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There is a command to help us:
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```bash
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$ docker port <containerID> 80
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32768
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```
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---
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## Manual allocation of port numbers
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If you want to set port numbers yourself, no problem:
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```bash
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$ docker run -d -p 80:80 nginx
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$ docker run -d -p 8000:80 nginx
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$ docker run -d -p 8080:80 -p 8888:80 nginx
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```
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* We are running three NGINX web servers.
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* The first one is exposed on port 80.
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* The second one is exposed on port 8000.
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* The third one is exposed on ports 8080 and 8888.
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Note: the convention is `port-on-host:port-on-container`.
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---
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## Plumbing containers into your infrastructure
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There are many ways to integrate containers in your network.
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* Start the container, letting Docker allocate a public port for it.
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<br/>Then retrieve that port number and feed it to your configuration.
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* Pick a fixed port number in advance, when you generate your configuration.
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<br/>Then start your container by setting the port numbers manually.
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* Use a network plugin, connecting your containers with e.g. VLANs, tunnels...
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* Enable *Swarm Mode* to deploy across a cluster.
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<br/>The container will then be reachable through any node of the cluster.
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When using Docker through an extra management layer like Mesos or Kubernetes,
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these will usually provide their own mechanism to expose containers.
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---
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## Finding the container's IP address
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We can use the `docker inspect` command to find the IP address of the
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container.
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```bash
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$ docker inspect --format '{{ .NetworkSettings.IPAddress }}' <yourContainerID>
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172.17.0.3
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```
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* `docker inspect` is an advanced command, that can retrieve a ton
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of information about our containers.
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* Here, we provide it with a format string to extract exactly the
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private IP address of the container.
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---
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## Pinging our container
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We can test connectivity to the container using the IP address we've
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just discovered. Let's see this now by using the `ping` tool.
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```bash
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$ ping <ipAddress>
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64 bytes from <ipAddress>: icmp_req=1 ttl=64 time=0.085 ms
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64 bytes from <ipAddress>: icmp_req=2 ttl=64 time=0.085 ms
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64 bytes from <ipAddress>: icmp_req=3 ttl=64 time=0.085 ms
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```
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---
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## Section summary
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We've learned how to:
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* Expose a network port.
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* Manipulate container networking basics.
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* Find a container's IP address.
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In the next chapter, we will see how to connect
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containers together without exposing their ports.
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???
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:EN:- Exposing single containers
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:FR:- Exposer un conteneur isolé
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