Docker Compose Foundations: Services, Images, Builds, Networks, Volumes, Environment, and Project Lifecycle: Configuration, Design Choices, and Tradeoffs

1. image: versus build:: artifact consumption versus artifact production

image: identifies a runnable artifact. It can be a tag or digest reference. build: describes how Compose should build an image from source. A service may contain both; current Compose then follows pull/build policy rules. If no pull_policy is provided, Compose can attempt to pull the image before building when both are present.

2. Default network versus explicit networks

The default project network is often ideal for a small local application: every service joins one bridge and is discoverable by service name. Explicit networks become valuable when you need segmentation, different connectivity domains, or a deliberate external network boundary.

Do not confuse network declaration with application reachability. A container can be attached to the expected network while the application listens on the wrong interface/port. Conversely, a published host port is not required for service-to-service communication on the same project network.

3. Named volume versus bind mount

A good rule: application data that must survive replacement needs an explicit durability design. Named volumes are convenient locally, but “named volume” is not synonymous with “backed up.”

4. env_file, environment, and interpolation solve different problems

Interpolation parameterizes the Compose model before it is sent to the Engine. environment and env_file populate the container environment. The shell, --env-file, default .env, Compose attributes, CLI runtime overrides, and image ENV participate in different precedence chains.

For non-secret configuration, keep source ownership obvious: use required-variable syntax for values that must be supplied and docker compose config --environment to verify interpolation. For secrets, use a secrets mechanism appropriate to the runtime; do not commit secrets into .env simply because Compose can read it.

5. Project naming: deterministic isolation versus accidental collisions

Explicit project naming is useful in CI, parallel feature branches, classroom labs, and shared developer hosts. If two invocations unintentionally resolve to the same project name, one can reconcile or tear down resources the other operator thought were separate.

# Highest-precedence explicit choice for one invocation:
docker compose -p da-compose15-a config --quiet

# Another isolated instance from the same Compose source:
docker compose -p da-compose15-b config --quiet

Record the project name in evidence. Do not diagnose a “missing service” until you have proved you are targeting the expected project and Docker context.

6. Foreground versus detached workflow

Foreground docker compose up streams attached logs and is excellent for small development/test runs where terminal lifetime is intentional. Detached up -d returns control to the operator and requires explicit ps, logs, health, and application probes. Neither mode makes the application more production-ready by itself.

7. Decision table: choose based on state ownership

8. Worked scenario: a test environment must be repeatable and auditable

Assume CI receives a release image digest and must execute integration tests. Prefer an explicit project name derived from a non-secret job ID, the release image by digest, a project-local default network, and a disposable named volume if persistence is needed only within the job. Save docker compose config and compose ps --format json. Tear down the project after evidence capture; delete the exact test volume only if the job's data-retention policy says it is disposable.

This design avoids rebuilding a release during promotion, avoids mutable-tag ambiguity, and makes project ownership visible through labels.

9. Keep state layers separate while evaluating a Compose choice

• Host/client/context: Docker context, filesystem paths, CLI and Compose versions.
• Build/image: source revision, builder, image ID/digest, cache.
• Container/process: command, PID, exit state, health.
• Network: network attachment, DNS, published ports, application listener.
• Storage: writable layer, named volume, bind source, backup.
• Identity/trust: registry authentication/authorization and artifact verification.

A single Compose file references all of these layers, but it does not collapse them into one state.

Knowledge check

Official references and version notes

• Docker Docs — Compose application model: projects, services, networks, volumes, and lifecycle.
• Docker Docs — Compose Specification reference: current declarative model and attributes.
• Docker Docs — docker compose config: canonical rendering, interpolation environment, service/network/volume views, hashes and digest resolution.
• Docker Docs — project naming: precedence and isolation.
• Docker Docs — interpolation and container environment precedence.
• Docker Docs — Compose networking: default network and service-name discovery.
• Docker Docs — docker compose down: default teardown and explicit volume deletion semantics.
• Docker Compose v5.5.1 release (2026-09-03). Labs record the actually installed version and do not assume every host matches upstream.