Docker Compose Recipes For Local Dev Practice Exam

Question 1 Docker Compose Recipes For Local Dev

Pin to image digest?

stop_signal: SIGINT — useful for apps that don't handle SIGTERM gracefully. image: nginx@sha256:abcd... — guaranteed identical bits. restart: unless-stopped user: '1000:1000' — avoids root-owned files when bind-mounting source.

Question 2 Docker Compose Recipes For Local Dev

Use a different Dockerfile per env?

ipc: 'host' — security risk; avoid if possible. docker compose run --rm -it web bash — default is interactive; -T disables TTY. --project-directory PATH or env COMPOSE_PROJECT_DIR. build: context: . dockerfile: Dockerfile.prod

Question 3 Docker Compose Recipes For Local Dev

Detect OOM kills?

Activates one or more profiles without CLI flag: COMPOSE_PROFILES=dev,debug docker compose up. docker inspect <id> | grep -i oomkilled — true if kernel OOM killer triggered. docker compose down (no -v). ${VAR:-default} — used if VAR is unset or empty.

Question 4 Docker Compose Recipes For Local Dev

External network use?

Use the modern format: omit version: entirely — Compose v2+ no longer requires it and infers from features. networks: shared: external: true — joins a network created outside this compose file. environment: - discovery.type=single-node - xpack.security.enabled=false Another container, another Compose project, or a host process already binds the same port. Change host port: ports: - '8081:80'.

Question 5 Docker Compose Recipes For Local Dev

Run a one-off init container that exits?

Service with restart: 'no'; depends_on can wait on it via condition: service_completed_successfully. docker compose port web 80 deploy.resources.limits.memory: 512M — kernel kills if exceeded. environment: - discovery.type=single-node - xpack.security.enabled=false

Question 6 Docker Compose Recipes For Local Dev

SQL dump from Postgres container?

Another container, another Compose project, or a host process already binds the same port. Change host port: ports: - '8081:80'. docker compose exec db pg_dump -U postgres -d mydb > backup.sql ipc: 'host' — security risk; avoid if possible. Mount SQL files into /docker-entrypoint-initdb.d/ for Postgres/MySQL — runs once on empty data dir.

Question 7 Docker Compose Recipes For Local Dev

Verbose Compose output?

${VAR:?error message} — Compose errors out if VAR isn't set. Compose passes through to buildkit; specify build stage target: build: target: prod. --verbose flag or COMPOSE_HTTP_TIMEOUT tuning for slow networks. Files in /docker-entrypoint-initdb.d/ run alphabetically — prefix with 01_, 02_ to control order.

Question 8 Docker Compose Recipes For Local Dev

Set replicas count declaratively?

deploy: replicas: 3 — only used by Swarm; for local Compose use up --scale. docker compose up -d --force-recreate Use the modern format: omit version: entirely — Compose v2+ no longer requires it and infers from features. labels: - 'org.opencontainers.image.source=...'

Question 9 Docker Compose Recipes For Local Dev

Sample minimal LAMP stack?

Services: php-fpm, nginx (mounts site.conf), mysql (volume + env). Link via Compose default network. .env file referenced via env_file, gitignored. For prod use real secrets manager. action: sync — copy changed files into running container. Service with restart: 'no'; depends_on can wait on it via condition: service_completed_successfully.

Question 10 Docker Compose Recipes For Local Dev

Hidden cost of using latest tag?

docker compose up -d --scale worker=3 environment: - KEY=value or env_file: .env POSTGRES_USER, POSTGRES_PASSWORD, POSTGRES_DB — create on first run. Unrelated upstream changes can break your build. Pin to specific tags or digests.

Question 11 Docker Compose Recipes For Local Dev

Restart policy "always" vs "on-failure"?

always restarts no matter what; on-failure[:N] restarts only on non-zero exit, optionally with retry cap. deploy.resources.limits.memory: 512M — kernel kills if exceeded. docker compose port web 80 volumes: - ~/.ssh:/home/node/.ssh:ro — security risk if image is shared.

Question 12 Docker Compose Recipes For Local Dev

Conditionally bring up dev tools?

Add a healthcheck on db; use depends_on: db: condition: service_healthy; in app, also retry connect on startup. docker compose run --rm web bash entrypoint: ['./wait-for-it.sh', 'db:5432', '--'] profiles: [dev] on adminer/mailcatcher containers — keeps prod runs clean.

Question 13 Docker Compose Recipes For Local Dev

Send container logs to syslog?

logging: driver: syslog options: syslog-address: 'tcp://localhost:514' depends_on: migrate: condition: service_completed_successfully MYSQL_ROOT_PASSWORD, MYSQL_DATABASE, MYSQL_USER, MYSQL_PASSWORD. --verbose flag or COMPOSE_HTTP_TIMEOUT tuning for slow networks.

Question 14 Docker Compose Recipes For Local Dev

Run a one-off command without modifying compose.yml?

Service with restart: 'no'; depends_on can wait on it via condition: service_completed_successfully. Use the modern format: omit version: entirely — Compose v2+ no longer requires it and infers from features. docker compose stats — Compose v2 shortcut. docker compose run --rm web bash

Question 15 Docker Compose Recipes For Local Dev

DNS configuration?

depends_on: migrate: condition: service_completed_successfully It only waits for the container to start, not for the service inside to be ready. Add healthcheck + service_healthy. dns: [8.8.8.8, 1.1.1.1] — useful behind corporate DNS that can't resolve public hosts. docker compose exec web sh (or bash if installed).

Question 16 Docker Compose Recipes For Local Dev

Run Compose under different project name?

docker compose -p myname up or set COMPOSE_PROJECT_NAME. build: context: ./app dockerfile: Dockerfile.dev healthcheck: disable: true docker compose version — should say v2.x+; v1 (Python) is end-of-life.

Question 17 Docker Compose Recipes For Local Dev

Strategy for slow first-time compose up?

Unescaped $ triggers compose interpolation. Use $$ in compose.yml to escape. Run from inside the Linux filesystem (/home/user/...) for best performance, not /mnt/c/. networks: backend: driver: bridge, then reference under service networks: [backend]. Pre-build images in CI and pull from registry rather than rebuilding locally.

Question 18 Docker Compose Recipes For Local Dev

Hot-reload Node app in Compose?

container_name: my-web — disables scaling; use sparingly. Add a healthcheck on db; use depends_on: db: condition: service_healthy; in app, also retry connect on startup. Mount source with ./src:/app/src, run nodemon or framework dev server inside container. Define a service per package needing isolation; share networks; use profiles to toggle subsets.

Question 19 Docker Compose Recipes For Local Dev

Mailhog for catching dev emails?

restart: unless-stopped — survives reboots but lets you stop deliberately. mailhog/mailhog image, expose 1025 (SMTP) and 8025 (UI). stop_signal: SIGINT — useful for apps that don't handle SIGTERM gracefully. .env file referenced via env_file, gitignored. For prod use real secrets manager.

Question 20 Docker Compose Recipes For Local Dev

Use a custom network driver (e.g., macvlan)?

Compose colors by default; --no-color to disable for piping.

networks:<br>  mac:<br>    driver: macvlan<br>    driver_opts:<br>      parent: eth0<br>    ipam:<br>      config:<br>        - subnet: 192.168.1.0/24

Use the modern format: omit version: entirely — Compose v2+ no longer requires it and infers from features. volumes: - ~/.ssh:/home/node/.ssh:ro — security risk if image is shared.

Question 21 Docker Compose Recipes For Local Dev

Postgres init script ordering?

Files in /docker-entrypoint-initdb.d/ run alphabetically — prefix with 01_, 02_ to control order. labels: - 'org.opencontainers.image.source=...' docker compose -p projname ps — useful when multiple Compose projects coexist. userns_mode: 'host' or userns_mode: 'keep-id' on Podman.

Question 22 Docker Compose Recipes For Local Dev

Difference between exited and dead container?

Unrelated upstream changes can break your build. Pin to specific tags or digests. DOCKER_HOST=ssh://user@host docker compose up — uses SSH transport. Exited: stopped normally.
Dead: stopped abnormally (process killed by OOM, daemon failure). Run uvicorn app:app --reload or use watchexec/watchdog for non-ASGI apps.

Question 23 Docker Compose Recipes For Local Dev

Why "depends_on" alone isn't enough?

docker volume ls — Compose names them <project>_<volume>. It only waits for the container to start, not for the service inside to be ready. Add healthcheck + service_healthy. deploy.resources.limits.memory: 512M — kernel kills if exceeded. profiles: [manual] — service starts only with --profile manual.

Question 24 Docker Compose Recipes For Local Dev

Run inside named project?

docker compose -p projname ps — useful when multiple Compose projects coexist. command: ['npm', 'run', 'dev'] .env file referenced via env_file, gitignored. For prod use real secrets manager. macOS/Linux: sudo lsof -iTCP:8080 -sTCP:LISTEN or ss -ltn.

Question 25 Docker Compose Recipes For Local Dev

Best practice: bind-mount node_modules?

Validates and prints the fully resolved Compose file with env interpolation applied. docker compose build web Don't — instead use anonymous volume to hide host's node_modules: - /app/node_modules after - ./:/app. docker compose version — should say v2.x+; v1 (Python) is end-of-life.

Question 26 Docker Compose Recipes For Local Dev

Compose run with override for one variable?

command: ['redis-server', '--requirepass', '${REDIS_PASSWORD}'] docker compose run -e FOO=bar web command docker compose cp web:/etc/nginx/nginx.conf ./nginx.conf docker compose pull && docker compose up -d

Question 27 Docker Compose Recipes For Local Dev

Force-kill all containers in project?

user: '1000:1000' — avoids root-owned files when bind-mounting source. WEB_PORT=4000 docker compose up — only works if compose.yml uses ${WEB_PORT} interpolation. guest/guest from localhost only; mount a definitions.json or use env vars for real creds. docker compose kill — sends SIGKILL; kill -s SIGINT to send a different signal.

Question 28 Docker Compose Recipes For Local Dev

Common gotcha: containers can't reach 'localhost'?

Use the modern format: omit version: entirely — Compose v2+ no longer requires it and infers from features. docker inspect <id> | grep -i oomkilled — true if kernel OOM killer triggered. Inside a container, localhost means the container itself. Use the service name (db) or host.docker.internal (Docker Desktop). Compose project = local; Stack = Compose deployed to Swarm via docker stack deploy.

Question 29 Docker Compose Recipes For Local Dev

Override the entrypoint?

It only waits for the container to start, not for the service inside to be ready. Add healthcheck + service_healthy. Compose handles dev nicely; Helm/Kustomize for prod. Keep compose.yml for local DX even after K8s adoption. entrypoint: ['./wait-for-it.sh', 'db:5432', '--'] Service name typo, or wrong working directory — Compose only loads docker-compose.yml in the current dir unless -f is set.

Question 30 Docker Compose Recipes For Local Dev

Debug compose interpolation by printing one var?

command: ['redis-server', '--appendonly', 'yes'] + volume on /data. docker compose config | grep MYVAR Use ARG in Dockerfile + build.args in Compose, not ENV. Set deploy.resources.limits.memory realistically, or fix the memory leak in the app.

Question 31 Docker Compose Recipes For Local Dev

Use buildkit cache from registry?

build: cache_from: ['myregistry/web:cache'] + cache_to: in CI. docker compose rm -f working_dir: /usr/src/app restart: unless-stopped

Question 32 Docker Compose Recipes For Local Dev

Anonymous volume?

volumes: - /var/lib/postgresql/data — Docker creates one; survives container restarts but not down -v. Set MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD — enables auth on first run. Run uvicorn app:app --reload or use watchexec/watchdog for non-ASGI apps. Run from inside the Linux filesystem (/home/user/...) for best performance, not /mnt/c/.

Question 33 Docker Compose Recipes For Local Dev

Stop grace period?

docker compose exec web env | sort stop_grace_period: 30s — waits before SIGKILL. Running processes inside each service's container. profiles: [manual] — service starts only with --profile manual.

Question 34 Docker Compose Recipes For Local Dev

Convert compose.yml to Kubernetes manifests?

Use kompose convert; review output, never deploy blindly. volumes: - ./dist:/usr/share/nginx/html:ro with a config that falls back to index.html for SPA routes. Compose passes through to buildkit; specify build stage target: build: target: prod. MYSQL_ROOT_PASSWORD, MYSQL_DATABASE, MYSQL_USER, MYSQL_PASSWORD.

Question 35 Docker Compose Recipes For Local Dev

Scale a stateless service to 3 replicas?

docker compose up -d --scale worker=3 <project>_default — services on this network can resolve each other by service name. action: sync — copy changed files into running container. docker compose logs -f web

Question 36 Docker Compose Recipes For Local Dev

Run container with privileged mode?

profiles: [manual] — service starts only with --profile manual. deploy: replicas: 3 — only used by Swarm; for local Compose use up --scale. Don't — instead use anonymous volume to hide host's node_modules: - /app/node_modules after - ./:/app. privileged: true — almost never needed; equivalent to bypassing many security controls.

Question 37 Docker Compose Recipes For Local Dev

Common cause: bind mount empty inside container?

ports: - '5432:5432' publishes to host.
expose: - '5432' reachable only on the Compose network. Path mismatch (host path doesn't exist, or relative path resolved from compose file dir, not where you ran docker compose). ${VAR:-default} — used if VAR is unset or empty. pull_policy: always|missing|never — controls when Compose pulls before running.

Question 38 Docker Compose Recipes For Local Dev

Define a profile so a service starts only with a flag?

next dev + postgres (+ redis for sessions) — anonymous volume on node_modules. profiles: - debug then docker compose --profile debug up. logging: driver: json-file options: max-size: '10m' max-file: '3' COMPOSE_FILE=base.yml:override.yml (colon-separated; semicolon on Windows).

Question 39 Docker Compose Recipes For Local Dev

Rebuild after Dockerfile changes?

docker compose build (or up --build). volumes: - type: bind source: ./src target: /app/src consistency: cached deploy: resources: reservations: devices: - capabilities: [gpu] environment: - HOME (no value) — Compose pulls from host env.

Question 40 Docker Compose Recipes For Local Dev

Strict interpolation (fail if unset)?

${VAR:?error message} — Compose errors out if VAR isn't set. docker compose exec -T db psql -U postgres -d mydb < backup.sql volumes: - ~/.ssh:/home/node/.ssh:ro — security risk if image is shared. docker compose build (or up --build).

Question 41 Docker Compose Recipes For Local Dev

Skip pulling images?

Containers from old service definitions still exist. Remove with --remove-orphans on up or down. docker compose up --no-pull — uses local copy or fails. deploy: resources: reservations: devices: - capabilities: [gpu] build: context: . dockerfile: Dockerfile.prod

Question 42 Docker Compose Recipes For Local Dev

Compose with reload-on-change for Go binary?

Use air (or cosmtrek/air image) — watches source, rebuilds, restarts. Bind ports 80/443, mount Caddyfile, Caddy fetches Let's Encrypt cert automatically. logging: driver: fluentd options: fluentd-address: 'localhost:24224' tag: web Running processes inside each service's container.

Question 43 Docker Compose Recipes For Local Dev

Disable IPC namespace sharing?

Auth pulls with docker login; consider a registry mirror or cache image in CI. volumes: - .:/app over an image with /app/node_modules wipes them. Use anonymous volume to preserve. CLI -e > environment: > env_file: > shell env > Dockerfile ENV. ipc: 'private' — default in modern Docker.

Question 44 Docker Compose Recipes For Local Dev

Set memory reservation (soft)?

--verbose flag or COMPOSE_HTTP_TIMEOUT tuning for slow networks. deploy.resources.reservations.memory: 256M — guaranteed minimum; not enforced limit. docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d build: context: ./app dockerfile: Dockerfile.dev

Question 45 Docker Compose Recipes For Local Dev

Use a build secret (BuildKit) in Dockerfile via Compose?

Define a service per package needing isolation; share networks; use profiles to toggle subsets. Docker Desktop not running, or socket path wrong (Linux: sudo systemctl start docker; usermod -aG docker $USER for permissions). build: secrets: [npm_token] + secrets: npm_token: file: ./npm_token — RUN with --mount=type=secret. Compose colors by default; --no-color to disable for piping.

Question 46 Docker Compose Recipes For Local Dev

Define a healthcheck for a Postgres container?

user: "${UID}:${GID}" in compose + export UID/GID in shell or .env. healthcheck: test: ['CMD-SHELL','pg_isready -U postgres'] interval: 5s retries: 10 deploy.resources.limits.memory: 512M — kernel kills if exceeded. Use docker-compose.override.yml (auto-merged in dev) and -f docker-compose.yml -f docker-compose.prod.yml in prod.

Question 47 Docker Compose Recipes For Local Dev

Add capabilities to a container?

depends_on: migrate: condition: service_completed_successfully Run uvicorn app:app --reload or use watchexec/watchdog for non-ASGI apps. Keep base file with shared services, add docker-compose.override.yml (dev) auto-loaded, and docker-compose.prod.yml opt-in via -f. cap_add: [NET_ADMIN, SYS_PTRACE] — minimize for security; drop with cap_drop: [ALL].

Question 48 Docker Compose Recipes For Local Dev

Kafka in Compose (KRaft mode)?

depends_on: db: condition: service_started — same as short form; the default condition. environment: KAFKA_KRAFT_MODE: 'true' + a few KAFKA_* vars; bitnami images simplify this. profiles: [dev, debug] — service starts if any matching profile is active. docker compose ps shows status; docker compose logs web shows stderr.

Question 49 Docker Compose Recipes For Local Dev

Difference between .env file and env_file:?

docker compose build web build: secrets: [npm_token] + secrets: npm_token: file: ./npm_token — RUN with --mount=type=secret. .env auto-loaded for interpolation in compose.yml; env_file: populates env vars inside containers. stop_grace_period: 30s — waits before SIGKILL.

Question 50 Docker Compose Recipes For Local Dev

What's the difference between Compose project and stack?

php-fpm + nginx + mysql + redis + queue worker; queue runs in its own service with the app image and php artisan queue:work. Compose project = local; Stack = Compose deployed to Swarm via docker stack deploy. ipc: 'host' — security risk; avoid if possible. docker compose exec db pg_dump -U postgres -d mydb > backup.sql