Configuration

By default, Compose pulls an image when it’s missing locally and uses the cached one otherwise. pull_policy lets you change that behavior per service. The policies services: web: image: nginx pull_policy: always Available values: missing (default when no build: is defined): pull only if the image is not present locally. Alias: if_not_present. Note: the latest tag is always pulled even with this policy. always: pull on every up, even if the local image is recent never: don’t pull, fail if the image is missing build: build the image, rebuilds even if it’s already present locally daily: check the registry if the last pull was more than 24 hours ago weekly: check the registry if the last pull was more than 7 days ago every_<duration>: check the registry if the last pull was older than the given duration. Units: w, d, h, m, s (or any combination, e.g. every_12h, every_30m, every_1d12h) When to use each always for development against a fast-moving tag: ...

Not everything in your stack is a container. Managed databases, SaaS APIs, VPN tunnels, Kubernetes intercepts, all sit outside Docker but still need to be wired into your local environment. Compose 2.36 introduced provider services to declare and manage these alongside your containers. The syntax A provider service replaces image: with a provider: block: services: api: image: my-api:latest tunnel: provider: type: telepresence options: namespace: avatars service: api port: 5732:api-80 Two parts: ...

LLMs are now first-class citizens in Compose. The models top-level key lets you declare which models your application needs and wire them into your services, all in the same Compose file. Basic usage Declare a model at the top level, reference it from a service: models: smollm: model: ai/smollm2 services: app: image: myapp models: - smollm When the stack starts, Compose ensures the model is available locally and connects the app service to it. The container receives endpoint information via environment variables. ...

You’ve used secrets for sensitive data (Tip #22). For non-sensitive config files like nginx.conf or prometheus.yml, there’s a parallel feature: configs. Basic usage Define a config at the top level, reference it in a service: configs: nginx_conf: file: ./nginx.conf services: web: image: nginx configs: - source: nginx_conf target: /etc/nginx/nginx.conf The file is mounted read-only inside the container at the target path. No need to declare a volume mount manually. ...

The env_file key looks simple but has surprisingly rich behavior, you can load multiple files, mark some as optional, and control how they’re parsed. The two flavors of .env There are two completely different things called “.env” in Compose: The project .env file at the same level as compose.yml, used for interpolation of ${VAR} in the Compose file itself (see Tip #42) env_file: at service level, loaded as runtime environment variables inside the container This post is about the second one. ...