---
title: Developing with Docker
author: gitlab.com/xlgmokha/developing-with-docker
date: 2020-06-10
---

# Developing with Docker

Mo Khan

Backend Engineer

Composition Analysis, GitLab

# Agenda

* Definitions
* Architecture
* Start/Stop container (ps, start, stop)
* Getting a shell (run vs exec)
* Dockerfile
* Analyzing an image (dive, docker layers)
* Shrinking an image (compression, discuss the trade offs of having more v. less layers)

# Definitions

* Image: is like a class
* Container: is like an instance of a class (i.e. object)

# Definitions - Image/Container

* Person is a class definition
* "you" and "mo" are instances of the class Person
* instances of person can interact with one another

```ruby
class Person
  def fist_bump(other_person)
  end
end

mo = Person.new
you = Person.new

mo.first_bump(you)
```

# Definitions

Registry: stores images and makes them available to others

For example:

* https://index.docker.io
* https://registry.gitlab.com

```bash
curl -s -i https://index.docker.io/v2/alpine/tags/list
```

# Architecture

```text
        ----------
        | Client |
        ----------
        | build  |
        | pull   |
        | run    |
        ----------
            |
            V
      --------------
      | Host       |
      --------------
      | Daemon     |
      | Containers |
      | Images     |
      --------------
            |  A
            V  |
       ------------
       | Registry |
       ------------
       | Images   |
       ------------
```

https://docs.docker.com/get-started/overview/#docker-architecture

# $ docker image ls

```terminal8
docker image ls --format "table {{.ID}}\t{{.Repository}}\t{{.Tag}}\t{{.Size}}"
```

# $ docker ps

```terminal8
docker ps --format "table {{.ID}}\t{{.Image}}\t{{.Status}}"
```

# $ docker run -it alpine:latest cat /etc/os-release

```terminal32
docker run -it alpine:latest cat /etc/os-release
```

1. check if "alpine:latest" is on docker host
1. download "alpine:latest" from registry to docker host
1. start a container using the "alpine:latest" image


# Dockerfile

```file
path: examples/001/Dockerfile
relative: true
lang: docker
```

https://docs.docker.com/engine/reference/builder/

# FROM alpine:latest

Initializes a build stage and sets a Base Image.

```file
path: examples/001/Dockerfile
relative: true
lang: docker
```

# COPY "hello.rb"

Copy "hello.rb" from the host to
"/usr/local/bin/hello" within the Docker image.

```file
path: examples/001/Dockerfile
relative: true
lang: docker
```

```terminal8
tree ./examples/001
```

# Dockerfile - RUN

RUN a command from within the image and make "hello" executable.

```file
path: examples/001/Dockerfile
relative: true
lang: docker
lines:
  start: 2
  end: 3
```

# Dockerfile - CMD

Set the default command to run when the docker image
is launched as a container.

```file
path: examples/001/Dockerfile
relative: true
lang: docker
lines:
  start: 3
  end: 4
```

# docker build -t developing-with-docker:latest examples/001/

```terminal32
docker build -t developing-with-docker:latest examples/001/
```

# docker run developing-with-docker:latest

```terminal32
docker run developing-with-docker:latest
```

# docker run -it developing-with-docker:latest /bin/sh

```terminal32
docker run -it developing-with-docker:latest /bin/sh
```

# docker ps

```terminal32
docker ps --format "table {{.ID}}\t{{.Image}}\t{{.Status}}"
```

# docker exec -it <imageid> /bin/sh

```terminal32
docker exec -it $(docker ps | grep developing-with-docker:latest | awk '{ print $1 }' | tail -n1) /bin/sh
```

# dive

```terminal32
dive $(docker ps | grep developing-with-docker:latest | awk '{ print $1 }' | tail -n1) /bin/sh
```

* Describe layers
* Downloading multiple layers in parallel vs 1 large layer

# Compression

More layers == more parallel downloads
Smaller layers == faster downloads per layer

# Compression (zstd)

* Deflate files within layers

```file
path: examples/002/Dockerfile
relative: true
lang: docker
```

# Compression (zstd)

* Inflate files when container is launched

```file
path: examples/002/run.sh
relative: true
lang: docker
```

# Compression

Before:

After:

# Summary

# Fin

Thank you for your time

[gitlab.com/xlgmokha/developing-with-docker](https://gitlab.com/xlgmokha/developing-with-docker)