Configuration

deploy.update_config, credential_spec, ports[].mode: host: every one of these is valid against the compose-spec schema, and none of them has ever done anything to a plain docker compose up. They’re Swarm-only. Before Compose 5.6.0, a file carrying any of them loaded without complaint, and whatever behavior you expected from reading the spec just never showed up, with no hint why. What changed Load a file with one of these attributes now, and Compose says so: ...

Tip #3 stopped at condition: service_healthy. The long-form depends_on syntax has three more fields, each solving a different problem: services: api: build: . depends_on: migrate: condition: service_completed_successfully cache: condition: service_started restart: true metrics: condition: service_started required: false service_completed_successfully: wait for a one-shot to finish service_healthy waits for a long-running service to become ready. service_completed_successfully waits for a service to exit, and only starts the dependent if it exited zero: ...

Tips are back after the summer break, and there are three months of Compose releases to catch up on, v5.2.0 through v5.5.1 shipped while the series was paused. The biggest addition: native init containers, through a new pre_start lifecycle hook. What pre_start does Tip #41 covered post_start and pre_stop, which run a command inside the already-running service container. pre_start is different: each step runs in its own ephemeral container, created after the service container exists but before it starts. It also waits on the service’s own depends_on conditions first, so a step can talk to those dependencies exactly like the main service command does. ...

Almost every Compose CLI flag has an environment-variable counterpart. Setting them once in a project .env file, in your shell, or in CI removes the need to retype the same flags on every command — and makes the configuration of a stack visible to anything that reads the environment. The core set The variables you reach for most often: Variable What it sets CLI equivalent COMPOSE_FILE Path(s) to the Compose file(s) -f, --file COMPOSE_PATH_SEPARATOR Separator when listing multiple files (in COMPOSE_FILE) COMPOSE_PROJECT_NAME Project name -p, --project-name COMPOSE_PROFILES Profiles to enable --profile COMPOSE_ENV_FILES Project-level env files --env-file COMPOSE_PARALLEL_LIMIT Max parallel operations --parallel (on some subcommands) COMPOSE_IGNORE_ORPHANS Don’t warn about orphan containers (no flag) COMPOSE_REMOVE_ORPHANS Always remove orphans on up/down --remove-orphans COMPOSE_ANSI Control ANSI output (auto, never, always) --ansi COMPOSE_PROGRESS Progress style (auto, tty, plain, json, quiet) --progress COMPOSE_STATUS_STDOUT Send status messages to stdout instead of stderr (no flag) COMPOSE_MENU Disable the interactive Docker Desktop menu (no flag) The full list lives in the Compose docs. The table above covers the ones that show up in real workflows. ...

Named volumes are great for keeping data alive across container restarts. The default behavior mounts the entire volume root at the container target. Sometimes you want to mount only a sub-directory — for instance, a single service among many sharing the same named volume, each scoped to its own directory. The subpath option does exactly that. The basic shape services: app: image: myapp volumes: - type: volume source: shared-data target: /app/data volume: subpath: app volumes: shared-data: The named volume shared-data exists once on the host. The app container sees only the app/ directory of it mounted at /app/data. Other directories in shared-data are invisible to app. ...