Docker: Compose & Networking

Wire several containers together

One container is a program in a box. Several containers are a system, and a system has questions with exact answers: which files win at a mountpoint, which port a sibling dials, which of five places a variable is set actually reaches the process. This is those answers, drilled.

Start this projectSee the modules
Modules
5
Drills
0
Build steps
9
Time
~4h

Walk out able to

Read any Compose file and say what it will do before you run it — then write one to a specification and prove every constraint held.

What you work on

01

Services and teardown

What `up` creates, and what `down` leaves behind.

02

Volumes against bind mounts

Which set of files wins at one mountpoint, and why.

03

Names, networks and walls

Reach a service by name; keep one unreachable.

04

Ports and configuration

Publish on purpose; know which value the process reads.

What you get

Skills that stick

Every project mixes short lessons, focused drills and real build steps, so you finish with working code and the judgement behind it.

You will practise

  • What a project creates, and what a teardown keeps
  • Which files win when a mount lands on a path
  • Service names, networks and what they wall off
  • Published ports, and which value a process reads

Afterwards you can

  • Predict a mountpoint before you run it
  • Read a port mapping in both directions
  • Reach a service by name, on the right port
  • Find which of five sources set a value

Modules

Step by step

Each module builds on the last. Read a short lesson, drill it until it's second nature, then put it to work.

  1. 1

    One file, one running stack

    ~48 min

    Bring several services up from one file, and know what a teardown leaves on the disk.

    • LessonWhy several containers need a file4 min
    • LessonWhat `docker compose up` creates7 min
    • LessonWhat a teardown keeps9 min
    • LessonStarted is not the same as ready7 min
    • LessonWait for the right thing8 min
    • Build stepBring a two-service stack up8 min
    • Build stepWatch the data vanish5 min
  2. 2

    Volumes against bind mounts

    ~38 min

    Predict which files are visible at a mountpoint before anything runs.

    • LessonWho owns the bytes at a mountpoint8 min
    • LessonThe three rules at a mountpoint9 min
    • Build stepGive the store somewhere to live8 min
    • Build stepHide the data without deleting it6 min
    • Build stepWatch a copy-up happen7 min
  3. 3

    The network you did not configure

    ~42 min

    Reach a service by name, and put a service where nothing outside can reach it.

    • LessonReach a service by its name8 min
    • LessonA network is a wall, not a label8 min
    • Build stepDial one service from inside another12 min
    • Build stepPut a wall between two services14 min
  4. 4

    Publish a port on purpose

    ~31 min

    Read and write a port mapping in both directions, and know exactly what it binds.

    • LessonWhich side of the colon is the host8 min
    • LessonWhat a published port binds9 min
    • Build stepPublish a port and prove which is which14 min
  5. 5

    Configuration the process reads

    ~55 min

    Find which of five sources a value came from, then build the whole stack.

    • LessonFive places one variable can be set8 min
    • LessonWhat actually reaches the process9 min
    • Build stepFind out which value actually won12 min
    • LessonCompose a stack to a specification16 min
    • LessonProve every constraint held10 min

A taste of the code

compose.yaml
services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"       # a door on your machine -> the port inside

$ docker compose port web 80

0.0.0.0:8080

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Ready when you are.

Work through it at your own pace and pick up right where you left off.

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