---
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

https://gitlab.com/xlgmokha

Inspired by: gitlab-org/gitlab#216082

# Agenda

* Build (build)
* Start/Stop container (ps, start, stop)
* Getting a shell (run vs exec)
* Analyzing an image (dive, docker layers)
* Shrinking an image (compression, discuss the trade offs of having more v. less layers)
* Sharing an image (push, pull, authn)

# 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
```

# Docker - Architecture

```plantuml

```

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

# Dockerfile

A minimal Dockerfile:

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

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

# Dockerfile - FROM

> Initializes a build stage and sets a Base Image.

In this example the base image is alpine:latest.
By default this image will be fetched from the default Docker registry.
https://index.docker.io/

```file
path: examples/001/Dockerfile
relative: true
lang: docker
lines:
  start: 0
  end: 1
```

# Dockerfile - COPY

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

```file
path: examples/001/Dockerfile
relative: true
lang: docker
lines:
  start: 1
  end: 2
```

```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: 2
  end: 3
```

# docker build

```terminal32
bash -il
```

# docker ps

# docker start

# docker stop

# docker run

# docker exec

# dive

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

# Compression (zstd)

More layers == more parallel download
Smaller layers == faster downloads

# Distribution

# docker push

# docker pull

# docker login