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---
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)
|
