Explore essential concepts related to orchestrating and managing multiple containers using Docker Compose, including service dependencies, configuration strategies, and common command-line operations for multi-container applications. This quiz aims to deepen your understanding of practical tools and best practices within the docker-compose ecosystem.
When setting up a docker-compose.yml file to run a web application and a database together, which section is essential for specifying both containers as separate services?
Explanation: The 'services' section in a docker-compose.yml file is used to define and configure multiple containers, such as a web app and a database, as separate but orchestrated components. 'Images' refers to container images, not service definitions. 'Containers' is not a valid section in docker-compose.yml. 'Volumes' is used for data storage, not for defining service relationships.
If a backend service must not start before the database service is ready, which docker-compose directive would set this dependency in the configuration?
Explanation: 'depends_on' is the correct directive to indicate service startup order, ensuring, for example, that the backend waits for the database. 'Links' is deprecated and provides legacy network aliasing. 'Requires' and 'triggers' are not valid docker-compose directives and won't set up such dependencies.
To run five identical instances of a worker service defined in a compose file, which command would you use in the terminal?
Explanation: The correct command to run multiple replicas of a service is 'docker-compose up --scale worker=5'. The other options do not apply: 'docker-compose start worker-5' is not a valid syntax, 'build' is for image creation, and 'exec' is used to run commands in a running container, not scaling services.
Which docker-compose feature allows two services to access the same files on the host system, such as sharing log output or database files?
Explanation: 'Volumes' enable sharing of file data between services and the host, making it easy for containers to access common files. 'Networks' facilitate communication, not file sharing. 'Ports' expose services outside containers. 'Environments' set configuration through environment variables, not file access.
When passing sensitive information like passwords to services within a Compose file, which section is most appropriate for defining such values per service?
Explanation: The 'environment' section is used to pass variables such as passwords to containers, ensuring each service can access necessary configuration securely. 'Labels' add metadata but do not configure sensitive values. 'Command' specifies the container startup command. 'Dns' deals with networking, not service configuration data.