How can you link two Docker containers together?

Linking two Docker containers traditionally involves using the --link option. This option establishes a relationship between the containers, allowing them to communicate with one another directly. When using the --link flag, Docker sets up a secure connection between the containers by creating a private network that allows one container (the "linking" container) to access services and address information of another container (the "linked" container) via its container name.

This method also allows for environment variables to be automatically injected into the linking container, containing the linked container's information like IP address and port information. It is important to note that while container linking was once a popular method to enable communications between containers, Docker has since evolved to favor user-defined networks over linking, as they provide more flexibility, ease of use, and are better suited for larger, more complex application architectures.

Other options like --network allow for broader connectivity features but do not specifically provide the same direct linkage capability. The --attach flag is used for attaching your terminal to a running container's STDOUT and STDIN but does not facilitate linking. The --bridge option is related to connecting containers to a default bridge network but does not inherently link individual containers.