Docker Container CLI

Week 19 Day 2

Lecture Videos 1 (15 minutes)

Watch:

• Container Intro (12:00)

docker container run (Official documentation)

Usage:

docker container run [OPTIONS] image-name [COMMAND] [ARG...]

• You always need to specify the image—every container is based on an image.
• The optional "OPTIONS" are specified with a flag.
  • Any options you include will come before the image name
• Each image has a default command—that will be replaced if you specify a new command (after the image-name)

Commonly used flags for docker container run:

Pop quiz

1. Let's run a container based on the nginx image, in detached mode. We want to publish the contents of that container's internal port 80, to my localhost at port 8080.

2. Let's run a container based on the alpine image and name it "juice". We want to run it with an interactive terminal, and use the command sh.

3. Let's run a container based on the ubuntu image and name it "greet_doggo". We want the container to be removed automatically once it is stopped. Let's have it use the command echo hi juice.

Pop quiz (answer key)

docker container run -p 8080:80 -d nginx

docker container run -it --name juice alpine sh

docker container run --name greet_doggo --rm ubuntu echo hi juice

docker container ls (Official documentation)

Purpose: list containers (can be used interchangeably with docker ps)

• -a flag includes stopped containers

Usage:

docker container ls [OPTIONS]

docker container stop (Official documentation)

Purpose: stop a container (or containers) that is currently running.

Usage:

docker container stop [OPTIONS] CONTAINER [CONTAINER...]

docker container start (Official documentation)

Purpose: start a stopped container (or containers)

• this will not create a new container, the container must already exist

Usage:

 docker container start [OPTIONS] CONTAINER [CONTAINER...]

docker container rm (Official documentation)

Purpose: remove a container

• by default you can only remove stopped containers
• -f flag forces removal even if container is running

Usage:

 docker container rm [OPTIONS] CONTAINER [CONTAINER...]

docker container prune (Official documentation)

Purpose: remove all stopped containers

Usage:

 docker container prune [OPTIONS]

docker container exec (Official documentation)

Purpose: execute a command within a running container

• often useful for opening interactive shell (uses same -it flag as container run)

docker container exec [OPTIONS] CONTAINER COMMAND [ARG...]

Lecture Videos 2 (10 minutes)

Watch:

• Docker Networking (8:30)

Docker networks

Networks allow containers to communicate with each other, whether or not they are exposing ports to the host.
Official documentation

What is a network?

Networking with Docker

By default, containers are connected to the "bridge" network.

However, that network won't allow containers to communicate with one another—by default, containers are isolated.

Creating custom networks (Official documentation)

Creating a custom network will allow the containers on that network to interact with each other.

docker network create [OPTIONS] network-name

docker network ls

Networking demo [1/2]

Let's create a network, and attach containers to it so we can see how networked containers communicate.

For comparison, we'll use two containers that are on the default network.

# create a network based on the bridge driver, called "test-network"
docker network create --driver bridge test-network
# create two images on that network
docker container run -d --name c1 --network test-network nginx:alpine
docker container run -d --name c2 --network test-network nginx:alpine

# create two more images, without specifying a network
docker container run -d --name c3 nginx:alpine
docker container run -d --name c4 nginx:alpine

Networking demo [1/2]

# access the shell on one of our two networked containers
docker container exec -it c1 ash
# ping a container that is not on the network
ping -c 2 c3
# ping a container that is on the network
ping -c 2 c2


docker container exec -it c3 ash
ping -c 2 c1
ping -c 2 c4

Lecture videos 3 (20 minutes)

Watch:

• Persistant Data in Docker: Bind Mounts (9:00)
• Persistant Data in Docker: Volumes (8:30)

Docker volumes/bind mounts

Using bind mounts and volumes allows data to persist even after a container is gone.

Bind mounts directly mount the contents of a folder on your filesystem into your container.

Volumes are managed by Docker—so you wouldn't directly access the files, but can be accessed and modified from within a container.

Options for creating volumes/bind mounts

There are two different types of syntax you can use with docker container run to establish volumes and bind mounts. Both flags can create either volumes or bind mounts.

• -v and --mount flags have the same purpose.
• --mount is typically preferred as it is considered to be clearer.

docker container run -v ...
docker container run --mount ...

-v/--volume syntax

• Pass in the fields separated by a colon
• Order matters
• Docker will infer whether you want to use a bind mount or a volume based on whether the first field is a path or not

-v/--volume syntax

For bind mounts

• First field is the path to the file or directory on the host machine.
• Second field is the path to where it is mounted in the container.
• Third field for additional options.

-v absolute/path:/absolute/path/in/container

-v/--volume syntax

For volumes

• First field is name of the volume (can be skipped for an anonymous volume)
• Second field is the path to where it is mounted in the container
• Third field for additional options.

-v name:/absolute/path/in/container

--mount syntax

Pass in a series of <key>=<value> pairs in any order, separated by a comma.

Type must be "bind" for bind mounts, or "volume" for volumes

--mount syntax

for bind mounts

--mount type=bind,source=/absolute/path,target=/absolute/path/in/container

for volumes

--mount type=volume,source=name_of_volume,target=/absolute/path/in/container

Bind mounts

Official documentation

• Bind mounts connect a folder in your file system to a folder on your container
• Convenience in simple cases—any changes made in one place will change what's present in the other

Demo: Serve a Website [1/2]

First, create a folder called app in your current directory, and make an empty index.html file inside the folder.

# run an nginx:alpine-based container, in detached mode
# mount the /app folder into the container at the path where nginx serves
# its files from (/usr/share/nginx/html)
# and expose port 80 to view the contents
docker container run -d \
--mount type=bind,source="$(pwd)/app",target=/usr/share/nginx/html \
-p 8080:80 nginx:alpine

Demo: Serve a Website [2/2]

Once your container is running, visit localhost:8080—you should see a blank page. Add some content to your html page, then save and refresh localhost:8080. Now you can see the new content you added, because the contents of your folder stays in sync with the contents of the folder inside your container.

Volumes

Official documentation
Volumes are managed from within Docker—don't depend on your file structure.

You wouldn't modify the contents directly (only from inside a container), but you can use it to spin up new containers with same contents.

Instead of providing a path to the folder (like you would with a bind mount) you can provide the name of the volume.

Demo: Persist data from a postgres instance that runs in a container

# pull the postgres image so we can inspect it
docker pull postgres
# inspect the image to find out what the path to the volume should be
# and what port we want to expose
docker image inspect postgres

Demo: Persist data from a postgres instance that runs in a container

# run the container (no volume)
docker container run -p 5431:5432 \
-e POSTGRES_PASSWORD=password \
--name postgres5431 -d postgres
# run the container with a volume named "postgres-data"
# that corresponds to the path where a postgres container stores its data (/var/lib/postgresql/data)
docker container run -p 5431:5432 \
-e POSTGRES_PASSWORD=password \
--name postgres5431 -d \
--mount type=volume,source=postgres-data,target=/var/lib/postgresql/data postgres
# now use the psql command line tool to connect
# to the postgres instance running in our container
psql -p 5431 -h localhost -U postgres -W