I Can Docker

What is this Docker?
Contain Errs
Docker World^TM
Running your first container
Containerizing an application
Managing Docker via CLI: How your life can be improved with just a few hundred of hours practice...
What’s that? Ah - Production? Don’t talk about - production? You kidding me? Production? I just hope we can run this container!

1. What is this Docker?

Docker and containers

Docker helps you create a reproducible environment.
- Your application is run inside an isolated environment.
You are able to specify the OS, the exact version of different libraries, different environment variables and their values among other things.
- Containers contain everything you need to run an application, including the source code you wrote.

Why should you use it?

Local environment setup is annoying
- (brew install <app> more like "brew is upgrading - maybe find something else todo")
Environments looks the same
Works on my machine
Modularization and separation of concerns
Makes it easy to create multiple micro-services that are written in different programming languages and that are using different versions of the same lib and even the same OS.

2. Contain Errs

Container != Virtual Machine (VM)
- Containers and VMs are similar in their goals: to isolate an application and its dependencies into a self-contained unit that can run anywhere.
- Remove the need for physical hardware, allowing for more efficient use of computing resources
A VM is essentially an emulation of a real computer that executes programs like a real computer. VMs run on top of a physical machine using a “hypervisor”. A hypervisor, in turn, runs on either a host machine or on “bare-metal”.
A container provides operating-system-level virtualization by abstracting the “user space”.

Container

Docker containers are self-dependent.
- All dependencies required by the container, including platforms and the actual application code, are packaged inside the container (different from standard Linux containers - for what it's worth).
Those dependencies are provided by the image that the container runs on top of. For our purposes, a container is a running instance of an image.

Image

An image is simply an ordered list of layers, which represent changes to the filesystem.
Since everything in Linux is a file, what these filesystem changes really represents are operations, such as the running of installation scripts.
- An image is really just an environment that resulted from sequential operations that are run to set up the environment.

Layer

Each of these operation produces a layer.
- Can be viewed as a point-in-time snapshot of the image at time of process.
- The next operation operates on the last layer, and builds on top of it.
In the end, you get an ordered list of sequentially-dependent layers, which make up the image.

A Running Container

When running a container, a new writable container layer is created on top of the read-only image (composed of read-only layers). Any file changes are contained within this new "top" container layer.
- These changes will not persist when the container is removed!
Image layers are never changed.

3. Docker World^TM

Want install? Click here and act now!
Container Registry (Docker Hub)
Docker Engine
- The Docker daemon and client, together, makes up the Docker Engine

4. Running your first container

# Just run it
docker run -it docker/surprise

# Get image
docker pull nginx:1.15.12

# Run container
docker run \
    --rm \
    -d \
    --name nginx \
    -p 80:80 \
    nginx:1.15.12

# Run container with custom content to be served by nginx
docker run \
    --rm \
    -it \
    --name \
    nginx \
    -p 80:80 \
    -v ~/zcode/quartz/I_Can_Docker/html:/usr/share/nginx/html:ro \
    nginx:1.15.12

# This is the part where one "exec's" into the container, and tries to
# delete a photo in the mounted dir but can't because it's "read only"
docker run \
    --rm \
    -it \
    --name nginx \
    -p 80:80 \
    -v ~/zcode/quartz/I_Can_Docker/html:/usr/share/nginx/html:ro nginx:1.15.12 \
    /bin/bash

Port syntax

-p [external (host) port]:[internal (container) port]

5. Containerizing an application

Dockerfile and Building Images

FROM
# Specifies the image (OS) used for the "base image"
# The first instruction in any Dockerfile

RUN
# The command(s) to run at build time.
# Each RUN instruction creates a new layer in the image.

ENTRYPOINT
# Path to the executable (with arguments) that should be run when the container is initiated
# If this is not specified, it defaults to the shell (/bin/sh -c)

CMD
# Specifies the default command to pass to the ENTRYPOINT when you run docker run.
# There should only be one, and only one in a Dockerfile.

Build Image

# cd into the correct dir
cd ./build_me

# Build image
docker build -t dockers:0.0.1 .

# Run it
docker run \
    --rm \
    -it \
    --name dockers \
    -p 3000:3000 \
    dockers:0.0.1

# Run it and set an environment variable
docker run \
    --rm \
    -it \
    --name dockers \
    -p 3000:3000 \
    -e SECRET="IsSafe?" \
    dockers:0.0.1

Other Dockerfile instructions to know

ENV
# Set environment variables that are available during build and run-time

COPY
# Copy the files from the build context to the directory specified
# Use over ADD when possible

WORKDIR
# Changes the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that comes after WORKDIR

EXPOSE
# Tells Docker which port(s) the container listens on at runtime.
# EXPOSE does not expose the port from the container to the host, it just tells Docker that the container is listening on that port.

USER
# Specify the user name or UID to use when building or running the image.

6. Managing Docker via CLI: How your life can be improved with just a few hundred hours of practice...

# List all images
docker image ls

# List all containers
docker ps -a

# Remove image
dr rmi

# Remove container
docker rm

# Stop container
docker stop
# SIGTERM

# Kill container
docker kill
# SIGKILL

# Get into running container
docker exec

# Inspect an image or container
docker inspect

# Get logs for container
docker logs -f