10 Running multiple environments with Docker Compose

This chapter revisits Docker Compose as the glue for running many environments—dev, test, UAT, and more—on a single Docker Engine while avoiding the drift that plagues manual deployments. It explains how Compose’s project concept (with default names derived from the folder, or overridden with a project name) lets you run multiple copies of the same app side by side, each isolated with its own network and non-conflicting ports. The aim is portability and consistency: the same container images behave appropriately in each environment through configuration, not code changes.

The core technique is using Compose override files to layer environment-specific settings onto a shared, minimal docker-compose.yml. Overrides merge from left to right, and the docker compose config command shows the effective result before deployment. Practical patterns include per-environment ports and networks, health checks tailored to non-production needs, and careful use of project names so up and down manage the correct resources. The chapter then covers configuration injection: direct environment properties, env_file for shared key-value sets, secrets for sensitive or file-based settings, and host-level variables substituted into Compose (including a .env file to define default ports, COMPOSE_FILE, and COMPOSE_PROJECT_NAME) so teams can spin up targeted environments without editing YAML.

To reduce duplication, the chapter introduces YAML extension fields (anchors and merges) that centralize common blocks—such as logging options or shared labels—and reuse them across services, with the caveat that extensions don’t span multiple files. The closing workflow emphasizes promoting the same tested image through every environment and only changing configuration, enabling reliable reproduction and faster feedback. Compose excels at running many isolated environments on one machine, but it demands disciplined naming, consistent file usage, and automation for deployment and teardown to keep management overhead low.

Repeating a Docker Compose command to start an app doesn’t run a second copy of the app.

Docker Compose builds names for the resources it manages by including the project name.

Specifying a project name lets you run multiple copies of the same app with one Compose file.

Removing duplication with override files that add environment-specific settings

Merging a Compose file with an override file and displaying the output

Running multiple isolated application environments in containers on a single machine

Running multiple environments on one Docker Engine, using networks for isolation

You need to use the same files and project name to manage an application with Compose.

Changing application behavior by applying configuration settings in Docker Compose

Using an environment file to specify the default for Docker Compose files and project names

Using the config command to process files with extension fields and check the result

Defining very different environments for the same app using Docker Compose

• Use a local database file
• Publish to port 8089
• Run v2 of the to-do application

• Use a separate database container
• Use a volume for the database storage
• Publish to port 8080
• Use the latest to-do application image

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