Both links and depends_on are used in a Docker Compose file (docker-compose.yml) to define relationships between containers. However, they differ in the way they establish these relationships.

Links

links is used to link a container to another container in the same Compose file. It creates a network connection between the linked containers, allowing them to communicate with each other. For example, if you have a web application container that depends on a database container, you can use links to ensure that the web application can access the database.

Here's an example of using links in a Compose file:

version: '3'

services:
  web:
    build: .
    links:
      - db
  db:
    image: postgres

In this example, the web service links to the db service, allowing it to connect to the Postgres database.

depends_on

depends_on, on the other hand, is used to define the order in which services are started. It does not create a network connection between the services, but rather ensures that one service starts before another. For example, if you have a web application container that depends on a database container, you can use depends_on to ensure that the database is started before the web application.

Here's an example of using depends_on in a Compose file:

version: '3'

services:
  web:
    build: .
    depends_on:
      - db
  db:
    image: postgres

In this example, the web service depends on the db service, ensuring that the database is started before the web application.

Summary

In summary, links is used to link containers and enable communication between them, while depends_on is used to define the order in which services are started.

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