Validasi YAML Docker Compose: 10 Kesalahan Sintaks Umum dan Cara Memperbaikinya

File YAML Docker Compose terlihat sederhana — sampai rusak. Satu spasi salah, indentasi keliru, atau karakter khusus tanpa tanda kutip menimbulkan error kriptik. Berikut 10 kesalahan paling umum dan cara memperbaikinya.

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Error 1: Tab bukan Spasi

Pesan error:

yaml: line 5: found a tab character where an indentation space is expected

Masalah: YAML melarang ketat karakter tab untuk indentasi.

Perbaikan: Ganti semua tab dengan spasi (2 spasi per level).

# BAD (tabs - invisible but breaks YAML)
services:
	web:
		image: nginx

# GOOD (2 spaces)
services:
  web:
    image: nginx

Tip editor: Aktifkan "Render Whitespace" di editor.

Error 2: Indentasi Tidak Konsisten

Pesan error:

yaml: line 8: mapping values are not allowed in this context

Masalah: Campuran level indentasi (2 spasi di sini, 4 di sana).

# BAD (inconsistent: 2 spaces then 4 spaces)
services:
  web:
      image: nginx     # 4 spaces - inconsistent!
      ports:
        - "80:80"

# GOOD (consistent 2 spaces)
services:
  web:
    image: nginx       # 2 spaces - consistent
    ports:
      - "80:80"

Error 3: Karakter Khusus Tanpa Kutip

Pesan error:

yaml: line 6: did not find expected key

Masalah: YAML menginterpretasi titik dua, hash, dan kurung secara khusus. Harus dikutip.

# BAD
services:
  web:
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb  # colon in value!
      - APP_TITLE=My App: The Best                       # colon in value!

# GOOD (quote values with special characters)
services:
  web:
    environment:
      - "DATABASE_URL=postgres://user:pass@db:5432/mydb"
      - "APP_TITLE=My App: The Best"

Karakter yang perlu dikutip: : { } [ ] , & * # ? | - < > = ! % @

Error 4: Format Pemetaan Port Salah

Pesan error:

services.web.ports contains an invalid type, it should be a number, or an object

Masalah: YAML dapat menginterpretasi 80:80 tanpa kutip sebagai base-60.

# RISKY (YAML may interpret as base-60)
services:
  web:
    ports:
      - 80:80        # Works but risky
      - 5432:5432    # May cause issues

# SAFE (always quote port mappings)
services:
  web:
    ports:
      - "80:80"
      - "5432:5432"
      - "127.0.0.1:3000:3000"

Error 5: Kunci Version Hilang atau Salah

Pesan error:

(root) Additional property version is not allowed

Masalah: Docker Compose v2 tidak lagi memerlukan kunci version.

# OUTDATED (Docker Compose v1 format)
version: "3.8"
services:
  web:
    image: nginx

# CURRENT (Docker Compose v2 - no version needed)
services:
  web:
    image: nginx

Dengan docker compose (v2): hapus version. Dengan docker-compose (v1): pertahankan.

Error 6: Variabel Lingkungan Mapping vs Daftar

Pesan error:

services.web.environment must be a mapping or an array

Masalah: Pencampuran sintaks mapping dan daftar untuk variabel lingkungan.

# Format A: List (with dashes)
services:
  web:
    environment:
      - NODE_ENV=production
      - PORT=3000

# Format B: Mapping (key: value)
services:
  web:
    environment:
      NODE_ENV: production
      PORT: 3000

# BAD: Mixing both formats
services:
  web:
    environment:
      NODE_ENV: production
      - PORT=3000          # ERROR: mixing formats!

Error 7: Nilai Boolean Tanpa Kutip

Pesan error: Tidak ada error terlihat, perilaku tak terduga.

Masalah: YAML menginterpretasi yes, no, true, false, on, off sebagai boolean.

# BAD (YAML converts to boolean true/false)
services:
  web:
    environment:
      FEATURE_FLAG: yes       # becomes boolean true, not string "yes"
      DEBUG: on               # becomes boolean true
      COUNTRY: NO             # becomes boolean false (Norway code!)

# GOOD (quote string values)
services:
  web:
    environment:
      FEATURE_FLAG: "yes"
      DEBUG: "on"
      COUNTRY: "NO"

Error 8: Kunci Duplikat

Pesan error: Sering tidak ada error — nilai kedua menimpa yang pertama.

# BAD (duplicate 'ports' key - second one silently wins)
services:
  web:
    image: nginx
    ports:
      - "80:80"
    environment:
      - NODE_ENV=production
    ports:                    # DUPLICATE! This replaces the first ports
      - "443:443"

# GOOD (combine under single key)
services:
  web:
    image: nginx
    ports:
      - "80:80"
      - "443:443"
    environment:
      - NODE_ENV=production

Error 9: Masalah Path Volumes

Pesan error:

services.web.volumes contains an invalid type

Masalah: Path Windows dengan backslash perlu tanda kutip.

# BAD (Windows paths without quotes)
services:
  web:
    volumes:
      - C:\Users\me\app:/app     # Backslashes cause issues

# GOOD (use forward slashes or quotes)
services:
  web:
    volumes:
      - "./app:/app"
      - "/home/user/data:/data"
      - "C:/Users/me/app:/app"      # Forward slashes on Windows

Error 10: Anchor YAML Salah Gunakan

Pesan error:

yaml: unknown anchor 'common'

Masalah: Referensi anchor (*nama) sebelum definisi (&nama).

# BAD (reference before definition)
services:
  web:
    <<: *common          # ERROR: 'common' not defined yet

x-common: &common
  restart: always

# GOOD (define anchor first, then reference)
x-common: &common
  restart: always
  logging:
    driver: json-file

services:
  web:
    <<: *common
    image: nginx
  api:
    <<: *common
    image: node:20

Checklist Validasi Cepat

Sebelum docker compose up, verifikasi:

1. Jalankan docker compose config untuk validasi sintaks
2. Periksa tab: grep -P '\t' docker-compose.yml
3. Kutip semua pemetaan port
4. Tidak ada kunci duplikat di level sama
5. Kutip nilai yang mengandung karakter khusus
6. Indentasi konsisten (2 spasi)

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Format output JSON dari "docker compose config" →