# Docker Lab 1: Hands-on section 1
###### tags: `Bremen_March_2020` `Docker`

## Playing with containers

There are different ways to use containers. These include:

* To run a **single task**: This could be a shell script or a custom app.
* **Interactively**: This connects you to the container similar to the way you SSH into a remote server.
* In the **background**: For long-running services like websites and databases.

## Run a single task "Hello World"

$ docker container run hello-world


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## Docker Hub (https://hub.docker.com/)


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### [`https://hub.docker.com/_/hello-world`](https://hub.docker.com/_/hello-world)


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### [`https://github.com/docker-library/hello-world`](https://github.com/docker-library/hello-world)


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## Run an interactive Ubuntu container

The following command runs an ubuntu container, attaches interactively ('`-i`') to your local command-line session ('`-t`'), and runs /bin/bash.

$ docker run -i -t ubuntu /bin/bash

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1. If you do not have the ubuntu image locally, Docker pulls it from your configured registry.
1. Docker creates a new container.
1. Docker allocates a read-write filesystem to the container, as its final layer.
1. Docker creates a network interface to connect the container to the default network. By default, containers can connect to external networks using the host machine’s network connection.
1. Docker starts the container and executes `/bin/bash`.
1. When you type `exit` to terminate the `/bin/bash` command, the container stops but is not removed. You can start it again or remove it.

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**By the way...**
In this rest of this lab, we are going to run an ==Alpine Linux== container. Alpine (https://www.alpinelinux.org/) is a lightweight Linux distribution so it is quick to pull down and run, making it a popular starting point for many other images.

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$ docker image pull alpine

$ docker image ls

Some examples:

$ docker container run alpine ls -l

$ docker container run alpine echo "hello from alpine"

$ docker container run alpine /bin/sh

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$ docker container run -it alpine /bin/sh

E.g.,:
`/ # ip a `

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## Docker container instances

$ docker container ls

$ docker container ls -a


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## Container Isolation

This is a critical security concept in the world of Docker containers! Even though each docker container run command used the same alpine image, each execution was a separate, isolated container. Each container has a separate filesystem and runs in a different namespace; by default a container has no way of interacting with other containers, even those from the same image.

So, let's see:

$ docker container run -it alpine /bin/ash
/ # echo "hello world" > hello.txt
/ # ls

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So let's check whether it is true...

To show which Docker containers are running:

$ docker ps

To show all Docker containers (both running and stopped):

$ docker ps -a

If you don't see your container in the output of either `docker ps` command, run it again:

$ docker run ...

If a container appears in `docker ps -a` but not in `docker ps`, the container has stopped, restart it:

$ docker container start <container ID>

If the Docker container is already running (listed in docker ps), reconnect to the container in each terminal:

$ docker exec -it <container ID> sh

### Detached containers

Starts an Alpine container running `ash`. The -dit flags mean to start the container **detached** (in the background), interactive (with the ability to type into it), and with a TTY (so you can see the input and output). Since you are starting it detached, you won’t be connected to the container right away.

$ docker run -dit --name alpine1 alpine ash

Use the docker `attach` command to connect to this container:

$ docker attach alpine1
/ #

Detach from alpine1 without stopping it by using the detach sequence, `CTRL + p CTRL + q` (*hold down CTRL and type p followed by q*).

### Finally:

$ docker container stop <node name> (or <container id>)

$ docker container rm <node name> (or <container id>)