How to connect two containers in Docker

Key takeaways:

• Connecting containers in Docker is crucial for enabling communication and resource sharing between them. Docker’s networking features, particularly bridge networks and Docker Compose, simplify the setup and management of these connections for complex applications.

• Docker networks help organize containers into logical groups for better communication. Containers use the bridge network by default, but users can also create custom networks. An example demonstrates building a Docker image with Ubuntu and the ping utility to test connectivity between two containers.

• After creating and running two containers, users can inspect their IP addresses and network IDs to confirm they are on the same network. Pinging between the containers verifies successful communication, highlighting the importance of inter-container connectivity in application development.

Connecting two containers in Docker allows them to communicate with each other and share resources. Docker’s networking capabilities, such as bridge networks and Docker Compose, make setting up and managing these connections easy. This is crucial for creating complex applications where different services need to interact. Docker facilitates this connectivity through networking features, enabling seamless integration and container interaction.

Using Docker networks

Docker networks offer a means of organizing containers into logical groups, facilitating communication between them. While creating and assigning containers to custom networks is possible, the default behavior is for all containers to use the bridge network. In the upcoming example, we will leverage this default behavior. Specifically, we will build a basic Docker image featuring an Ubuntu base with the addition of the ping utility. Subsequently, we will establish two containers and observe their intercommunication within the bridge network.

Example: Connecting containers

Run the following code and copy/paste the commands we have mentioned below to connect Docker containers:

This Dockerfile creates a Docker image based on the latest Ubuntu distribution and installs the ping utility. The RUN instruction performs the update of the package index and then installs the ping command, which is useful for testing network connectivity between containers.

Create and run the first container

After clicking the “Run” button, the image will start building. Subsequently, you can execute the following command to create the first container:

Create and run the second container

Upon running the above command, click on the “+” to open a new terminal and execute the following command to create and run the second container:

Inspect network IDs and IP addresses

Once you have created both containers, open another terminal to check each container's IP address and network ID. This step helps verify that both containers share the same network. Execute the following commands:

Similarly, inspect network ID and IP address of second container:

Testing the connection

Copy the IP addresses and use them to ping from one container to the other. Move to the first container and run the following to test the connection:

Similarly, in the second container, run the following to test the connection:

This will confirm intercommunication between the containers.

Note: Press “Ctrl+C” to stop the execution when needed.

Conclusion

By using Docker’s default bridge network, we’ve demonstrated how containers can communicate with each other. This is essential for services that need to interact within the same application or across distributed systems.