Docker Deep Dive 2: Dockerfiles, Multi-Stage Builds & Volumes

පිටුව 14: Docker රහස් 2: Dockerfiles ලිවීම, Multi-Stage Builds, Volumes සහ Networking

Dockerfile ලිවීම (FROM, WORKDIR, COPY, RUN, CMD vs ENTRYPOINT), Image Layers, Multi-Stage Builds (1GB -> 25MB), Persistent Volumes සහ Port Forwarding (-p).

15 Sept 20264 min readSelf Guide · Stage 11#Docker#Multi-stage#SRE Labs

Lab 14 of 20 · Docker Mastery · 5 hands-on activities · bilingual (English + සිංහල)

පිටුව 14: Docker රහස් 2: Dockerfiles ලිවීම, Multi-Stage Builds, Volumes සහ Networking

Dockerfile ලිවීම (FROM, WORKDIR, COPY, RUN, CMD vs ENTRYPOINT), Image Layers, Multi-Stage Builds (1GB -> 25MB), Persistent Volumes සහ Port Forwarding (-p).

💡 සරල සිංහලෙන්: Dockerfile, Layers සහ Volumes සරලව

කේක් හදන Recipe එක සහ කේක් එක (Image vs Container):

Dockerfile: කේක් එක හදන Recipe පොත. මොන ingredients ද ඕන (FROM), කොහොමද කලවම් කරන්නේ (RUN) කියලා ලියලා තියෙනවා.
Docker Image: කේක් එක හදන අච්චුව (Mould). මේක වෙනස් කරන්න බෑ (Read-only).
Docker Container: ඒ අච්චුවෙන් හදපු ඇත්තම කේක් එක! අපිට එකම Image අච්චුවෙන් Containers 100ක් වුණත් තත්පරයෙන් හදන්න පුළුවන්.
Multi-Stage Builds: කේක් එක හදන්න ගෙනාපු පිටි මෝල්, ලොකු මැෂින් ඔක්කොම පැත්තකට දාලා, අන්තිමට ලස්සන කේක් පෙට්ටිය විතරක් පාරිභෝගිකයාට දෙනවා වගේ. Image size එක 1GB ඉඳන් 25MB වෙනකම් අඩු වෙනවා!
Volumes: Container එක delete කළත් අපේ Database එකේ දත්ත මැකෙන්නේ නැතුව Hard disk එකේ තියාගන්න දාන Folder එකයි Volume කියන්නේ.

Architectural Foundation & Systems Diagram

Packaging microservices cleanly requires mastering the Dockerfile, understanding image layer caching, and safely mounting persistent storage volumes.

📄 Dockerfile Anatomy — • FROM: Base OS or runtime (e.g. alpine:3.19).
• WORKDIR: Active working folder.
• COPY: Transfer source code.
• RUN: Build/compile instructions.
• CMD: Default execution command.
📦 Multi-Stage Builds — Separate the build environment (with compilers, JDK, npm) from the runtime environment (minimal Alpine with only the compiled binary). Shrinks image sizes from 1.2 GB down to 25 MB!
💾 Volumes & Networks — Containers are ephemeral (data is lost on exit). Use -v /host/path:/container/path for persistent data (like databases), and -p 8080:80 to forward host ports into container ports.

Step-by-step practical lab

Step 01: Launch Detached Web Container with Port Forwarding

සිංහලෙන් — Port Forwarding සහිතව පසුබිමේ (Detached) Nginx Web Container එකක් run කරමු.

Run an Nginx container in background detached mode (-d), binding host port 8080 to container port 80 (-p 8080:80).

ExampleShell

docker run -d -p 8080:80 nginx

-d : Detached mode: Container එක පසුබිමේ (background) ධාවනය කරයි.
-p 8080:80 : Port forwarding: Host මැෂින් එකේ 8080 වරාය Container එකේ 80 වරායට සම්බන්ධ කරයි.

Expected output

Output

e3f89a21b402847291a24d081f7294bbca841029412958471204859182937401
Container launched successfully in detached mode (-d) with port binding 0.0.0.0:8080->80/tcp

SRE Tip: The 64-character alphanumeric string returned is the unique Container ID assigned by the container runtime.

Step 02: Inspect Running Docker Containers Status

සිංහලෙන් — Server එකේ සජීවීව දුවන Docker Containers ලැයිස්තුව පරීක්ෂා කරමු.

List all active running Docker containers with container ID, image name, port bindings, and uptime.

ExampleShell

docker ps

ps : ක්‍රියාත්මක වන containers පෙන්වයි. නැවතුණු සියල්ල බැලීමට -a යොදන්න.

Expected output

Output

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS         PORTS                  NAMES
e3f89a21b402   nginx:alpine   "/docker-entrypoint.…"   2 hours ago     Up 2 hours     0.0.0.0:8080->80/tcp   web-frontend
9a81b2c4d5e6   redis:7-alpine "docker-entrypoint.s…"   5 hours ago     Up 5 hours     6379/tcp               cache-redis

SRE Tip: If a container dies immediately upon startup, run 'docker ps -a' and check its Exit Code (e.g. Exit 137 = OOM killed).

Step 03: Query Cached Local Docker Images

සිංහලෙන් — පරිගණකයේ තැන්පත් වී ඇති Docker Images ලැයිස්තුව බලමු.

Query all container image blueprints, repository tags, image IDs, and sizes cached on the local Docker engine.

ExampleShell

docker images

images : Local disk එකේ ඇති සියලුම container blueprints පෙන්වයි.

Expected output

Output

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
nginx        alpine    9a4c1070e632   3 days ago     41.2MB
redis        7-alpine  178ec6b51347   1 week ago     38.6MB

SRE Tip: Alpine-based images are ~40MB, whereas Ubuntu/Debian base images are 150MB+. Smaller images reduce vulnerability attack surface!

Hands-on practice activities

Work through these yourself — tick them off as you go.

Activity 66: Query Cached Local Docker Images (Drill) — Query all container image blueprints, repository tags, image IDs, and sizes.
Activity 67: List Active Running Containers (Drill) — View active containers, their container IDs, images, status, and mapped port bindings.
Activity 68: Launch Detached Web Container with Port Forwarding (Drill) — Launch an Nginx container in background detached mode forwarding host port 8080 to container port 80.
Activity 69: CMD vs ENTRYPOINT Distinction (Checkpoint) — ENTRYPOINT specifies the immutable command binary; CMD specifies default arguments that can be overridden at runtime.
Activity 70: Multi-Stage Build Benefit Quiz (Quiz) — What is the primary benefit of Docker multi-stage builds? Answer: Dramatically reducing production container image size and attack surface.